THE UNIVERSITY OF ILLINOIS LIBRARY WON CIRCULAR Food Requirements of Pregnancy in Swine By H. H. MITCHELL, W. E. CARROLL, T. S. HAMILTON, and G. E. HUNT UNIVERSITY OF ILLINOIS AGRICULTURAL EXPERIMENT STATION BULLETIN 375 CONTENTS PAGE PLAN OF THE EXPERIMENT 468 EXPERIMENTAL RESULTS 469 Gains in Body Weight 469 Digestibility and Metabolizable Energy of Ration 470 Weights of Uteri and Contents at Different Stages of Gestation 470 Chemical Composition of Samples 478 Mathematical Analysis of Chemical Data 483 Nitrogen, Calcium, and Phosphorus Balances of Pregnant Gilts 495 SUMMARY 501 LITERATURE CITED. . . 504 Urbana, Illinois November, 1931 Publications in the Bulletin series report the results of investigations made by or sponsored by the Experiment Station Food Requirements of Pregnancy in Swine H. H. MITCHELL, W. E. CARROLL, T. S. HAMILTON, and G. E. HUNT" IN THE COURSE of his fundamental investigations of the nutrient requirements for milk production, Haecker** proceeded on the basis of the theorem that "in order to determine the actual net nutrients required to produce a given animal product, the composition of the product should be known .... Before a builder bids on a con- tract, he determines the quantity needed of each of the materials that are to appear in the structure. Without such specifications he would not know how much of each of the different materials would have to be provided." The statement implies, of course, that due recognition must be given to the possible transformation of nutrients in animal metabo- lism. With this thought in mind Haecker based his well-known feed- ing standards for milk production upon the composition of milk of different degrees of richness, and all American feeding standards for milk production have developed along the line initiated by Haecker. The conception that the composition of the product formed by an animal, whether it be milk, animal tissue, or egg, determines the nu- trient requirements for its formation, tho fundamentally sound, has not been extensively used in the formation of feeding standards other than those for milk production. Armsby's standards for the require- ments of net energy embody the same principle, altho his protein stand- ards are based upon less certain grounds. The principle has recently been applied by one of the authors 11 * of this bulletin to the general field of the protein requirements of cattle, while the case of pregnant swine is considered on the same basis in the experiment reported herein. No accurate and satisfactory estimate of the nutrients required by the pregnant female in the development of her young in utero can be made until the growth of the fetus and of the maternal nourishing and protective tissues has been measured and studied. The nutrients de- posited in the uterus during pregnancy represent in the strictest sense of the term the nutrient requirements of pregnancy. Obviously the intake of digestible nutrients must exceed these requirements, since the animal body does not utilize its digested food in anabolism to the extent of 100 percent; however, the excess of digestible nutrients needed will depend upon the percentage utilization of the protein, H. H. MITCHELL, Chief in Animal Nutrition; W. E. CARROLL, Chief in Swine Hus- bandry; T. S. HAMILTON, Associate in Animal Nutrition; and G. E. HUNT, Assistant in Swine Husbandry. 467 468 BULLETIN No. 375 [November, energy, minerals, etc., contained in the food and will vary with the nature of the diet. Hence the nutrients required for pregnancy cannot be expressed satisfactorily in terms of digestible food nutrients,. If the condition of pregnancy influences the metabolism of the maternal organism in such a way as to modify its requirements for nutrients, this influence must of course be considered in computing the food requirements of pregnancy. PLAN OF THE EXPERIMENT The purpose of the experiment was (1) to make a physical and chemical examination of the uterus and contents of gilts killed at dif- ferent stages of gestation; and (2) to determine the nitrogen, calcium, and phosphorus balances of gilts during the entire period of gestation. Sixteen gilts were used in the experiment, 9 of the Poland China breed, 6 of the Duroc- Jersey breed, and 1 of the Hampshire breed. They were all bred to the same Poland China boar. Five of the gilts were kept at the nutrition laboratory and were confined in metabolism crates continuously for 16 weeks in the case of 3 gilts, 15 weeks in one case, and 14 weeks in another. The remaining 11 gilts were kept at the swine barn and were fed as a single lot. All gilts were fed a ration consisting of 86 percent cracked corn, 6 percent alfalfa meal, 4 percent tankage, 3 percent linseed meal, and 1 percent ground limestone. This ration was found to contain by actual analysis 16.87 percent moisture, 10.94 percent crude protein, 3.13 percent ether extract, 3.51 percent crude fiber, 3.22 percent ash, 62.33 percent nitrogen- free extract, .608 percent calcium, .360 percent phosphorus, and .0241 percent iron. Its gross energy content was equivalent to 3.61 calories per gram. At the end of the fifth week of gestation the first gilt was sacrificed for examination, and at the termination of each of the subsequent weeks of gestation, up to and including the eleventh week, one gilt was slaughtered. Two gilts were slaughtered at the end of 12 weeks of gestation, one at the end of 13 weeks, two at the end of 14 weeks, one at the end of 15 weeks, and three at the end of 16 weeks. At slaughter the uterus and contents only were removed for ex- amination. Each uterus was opened and dissected into fetuses, mem- branes, amniotic fluids, and uterus, constituting five samples for chemi- cal analysis. Individual weights were taken on each fetus and its respective membranes and fluids, and the crown-to-rump measurement on each fetus was taken with a caliper. Partially absorbed fetuses were weighed but not added to any of the chemical samples. 1931] FOOD REQUIREMENTS OF PREGNANCY IN SWINE 469 Where grinding of the samples was necessary, a phosphor-bronze power meat chopper was used to avoid contamination with iron. Each chemical sample was analyzed for dry matter, nitrogen, ether extract, ash, iron, calcium, and phosphorus, and its gross energy was determined in the bomb calorimeter. The dry matter was determined by heating for 5 hours in an electric oven maintained at 105 C. The Kjeldahl method, with mercury and potassium sulfate additions pre- vious to digestion, was used in the determination of nitrogen, the ammonia formed being distilled into approximately 4 percent boric- acid solution, and titrated with standard sulfuric acid with a normality N N of either or , using brom-phenol-blue as an indicator. The samples were ashed in an electric furnace with a pyrometer attach- ment at temperatures of about 600 C. For materials difficult to ash at this temperature the carbon residue after treatment with HC1 was filtered off and burned separately. The ether soluble material was ex- tracted in Soxhlet extractors for 48 hours. The calcium was deter- mined by a modification of the McCrudden method, 9 * the phosphorus by the Pemberton-Kilgore volumetric method, 5 * and the iron by a modified Kennedy method. 7 * EXPERIMENTAL RESULTS The gilts \vere bred in January or February, 1928, and approxi- mately half of them were rebred before evidence of successful ferti- lization was obtained. Gains in Body Weight The gilts kept in outdoor lots had an average initial weight of 273 pounds and were hand- fed to gain approximately one pound daily. The average daily gain for the group, depleted from time to time as animals were removed for slaughter, was 1.05 pounds, and the average daily food consumption equaled 7.91 pounds. The five gilts confined in metabolism cages in the nutrition labora- tory, weighing initially from 235 to 295 pounds, were started on a daily intake of 6 pounds of feed per head, but their gains were so rapid that on February 16 the daily allowance was reduced to 5 pounds, which was readily cleaned up at all times. The average daily gains of these gilts from date of last mating to slaughter ranged from 1.04 to 1.27 pounds, the mean being 1.11 pounds. The much greater economy of gains in these confined gilts than in the group- fed gilts must have been the result of close confinement and possibly, to some extent, of a higher environmental temperature. 470 BULLETIN No. 375 [November, Digestibility and Metabolizable Energy of Ration During the latter part of January, while each of the gilts in the metabolism crates was consuming 6 pounds of ration daily, a digestion trial lasting 7 days was undertaken. The coefficients of digestion ob- tained are summarized in Table 1. Only four of the gilts were in- cluded in this trial, since one of the five originally put in the crates had just been replaced by another gilt, because of failure to become pregnant. TABLE 1. SUMMARY OF DIGESTION COEFFICIENTS Gilt No. Dry substance Crude protein N-free extract Crude fiber Ether extract 24 PC percl. 81.5 perct. 71.3 perct. 89.1 perct. 33.2 perct. 64.7 69-33 DJ 84.4 75.7 90.5 39.7 72.9 66 PC 84 3 76 7 91 1 39 9 59 8 39-90 PC 81 1 69 3 88.7 33 5 68 8 Average 82.8 73.2 89.8 36.6 66.5 The dry matter of the ration showed an average digestibility of 82.8 percent, the crude protein 73.2 percent, the crude fiber 36.6 per- cent, the nitrogen- free extract (mainly starch) 89.8 percent, and the ether extract (mainly fat) 66.5 percent. The gross energy of the feed and of the liquid and solid excreta was determined on composite samples from this digestion trial by means of the bomb calorimeter. The information obtained with ref- erence to energy utilization is summarized in Table 2. The energy content of the urine as observed has been increased to that which would have been obtained if all the food protein had been catabolized. This has been done by adding to the observed daily energy content of the urine, 7.45 calories for each gram of nitrogen stored daily in the body. Of the gross energy consumed 19.1 percent, on an average, was lost in the feces and 3.5 percent in the urine, leaving 77.4 percent to be metabolized in the body. Weights of Uteri and Contents at Different Stages of Gestation The gilts were slaughtered, either singly or in groups of two or three, at times ranging from 5 to 16 weeks after successful mating, the latter interval corresponding to the total length of gestation minus 2 or 3 days. The measurements taken on each uterus and its various contents are assembled in Table 3. On the last two gilts, slaughtered at the end of the sixteenth week of pregnancy, the weights of livers and spleens were taken for each fetus and these organs were then com- FOOD REQUIREMENTS OF PREGNANCY IN SWINE 471 CJ fit 1 ercenta metabo J s 1 1 2^ ^ OH 0) c v; iot~>on 10 D 3' ^ ,',.',' ^ 1 C * U 90 ' 1 1 0) t ) L| g g ^^^2 ^ a RATION Meta bo- 3 ? CS ^". n e 'c H E- * L- > u _ -> ^ ~ ||| ^ CN CS CS CN * CNCNCNCN C u o Z O "-> cj Q a, e II ^ 472 BULLETIN No. 375 1 ' W- *3S Average oo "- | -ooS 2 r.jo-g. < Average >o .-.oortes CSCN to Q 1 H -rfgg I -*jfi3 3 o ai v-1 r~ CM o H OtN D 2* Q ^^. a2| gs "* oo * n O> f*5 (N 1O n 3 100 E_: N -^^ s *** H - 3 t^.^ E a oti t~ IT) M pq f? '^ ^-MlOOOg N ^2^ | w 2 3 u 3 v ~'0-<*'t^ "S WJ "SJ o S 3 *s w 3 "o -2|| 2 g J S-gg^ H g O TJ-QO C hu cj | N 2 C *) o = * O W J> CO > JS P tt S5 C gestatio ^ to oo 1O vO gestatioi Evd 2SS 'a v bo E^o -" ^ f gestati 0^ i VO 3 IM E -Hfjoots *-f 00 CN l~* tscs W 4) ^> to 9 OS O MOO O IO1O O 3 "o Et^roO O g 5's O O & 3 o ^ a "o c ~""' s L of uter *. O. ^H ^H - k J 1O O* ^j a *- S 1' S s B SZ3 *i io2 t- E 3 Fetuses, sex. . Length. . . . Weight. . . . Membranes. . Liquids 8j =^'l : ll^ll l^ e S3 "55 ' 1931] FOOD REQUIREMENTS OF PREGNANCY IN SWINE 473 & 2 :- 2 :r oo I ;;.,, 1 :2^.ro < * 43 < I ooo -oo 1 10 >o * o *^ X "* Tf -^ 3 o H 10 "o H IO IOCS'* oo * oo gtscsiors MHi s ^^852 m ""^I^Soo W5W5 3 '*"iO>COO-i 10 t- a "S3?0 O c E;*2 -2o?^?o 01 o E O J3 ro-* I 3 - s ^oc'ooo O s 3 fON(S O *: N -= 5; w ' ? ^J _o ej 3 -ssss S C O - s * Q> Q 1 oo OO \ "o \ "o s ""-S5S CJ BO ^SK!5^ H I .M '"lO O V .* IN M 8 C3 1 J3 >*to 1 J3 w > EOt-ON cspg^t^ V JZ*z O ts 1 w ^ *^ VA 01 ri ^ ?o T 1 es^*i H CN S 1 U E^-cs 1 O o, as o 00 CS 1O CS Q cs 8 o Ij <* fi ^HCO^O 1 cs <*> cs , !5 '& x BO *"><* 00 "* Et^OOO- "*3S8 -sss cs2-*o cs ^(N CS Fetuses, sex... Length. . . . Weight. . . . Membranes. . Liquids Fetuses, sex. . . Length .... Weight Membranes. . Liquids Fetuses, sex.. Length. . . . Weight Membranes. . Liquids Fetuses, sex. . Length. . . . Weight Membranes. . Liquids 474 BULLETIN No. 375 I cS 00 )>Ot*> *f CS (N 6 -H 00 tN-^O ses, ngt eig Membra Liquids us Le We -< OOOMO S1OIO 00 u-, ^ 'H CS CS O ECSOOOO Fetuse Len Wei Memb Liquid Average o t- CSIOO Average =SlS8 5 o t- o 'o H CS W*t^-lO 10 -2s 3 C o Or^T* f uterus ^=11 3 o "o 1 V) C 00 O-O cs 1 u ^Sls 5 C o >f gestati -o r. -* '"csScsO O<*5CS j= TC a CJ 04 *-i cscs o\ 4 CS s.*. 2 3 ^OCSCS 3 IN 0^*5 3 = C O w a o E cs * ov o | .5? o 00 ii -SK8 _,VO~- CSO E CS-H 00 00 X . . m . &>..&*. J2- C . -3X! C3 K ' 3 ^> E'3 Fetuses, sex.. . Length Weight Membranes. . . Liquids FOOD REQUIREMENTS OF PREGNANCY IN SWINE 475 u 4) M 2 00 O "5 O fc ^o'lO^vO < YH CN CN < I0f0 "is 3 "! o H CN^VOO H ^HCNCN ~* OCNCN OCN- oo X-CNO-O 10 O\ 00 CN 00 E CNOOCN Tj 3 HI OJ W) 3 3 u 00 t^ CN CN "o ?> -H CNCN C 3 o "o u t3 _ J= 1O X- CNCN>O >O J OVT)< ^ >Oro ,2 CNti "H 3 S c 3 o 3 f) "2 5 i X-CNTj<-HCN CST)CN 1 ** 6 x- c*^ O ^^ O > M 10CN-H t Ov 1 " i i t^ O\00 CN x: i - U \ ** *". (< CN m xiCNoofnoo <^ CNCNt^ *^ t ""^OCN^ O HI ^ ^^ 3 V O 3 "o 1O i C _t^ OOO CN ECNOOOOO OCNCN 4J J3 M S a^ISS oo OOt^^CN - VO <-. rsO' co cs oioooio f*3 CO CS X . . m . V . . V . S ! '. o '. "* a ' If-all 3^^gg tS Sj "55 S : Ifil .-J> I) cc .U >^"? b 2 J 01 1 oo t^vfl s T *H CN ^ 'J* ^H > < - 3 1 t o o "cN^S^ fl O O T* C^ 0000 IO St^ IO O CN CNCNIO ^ - 3 oo *o *o O .^ O\00'O dcs CNt^-fOI3 "^ O CN ro ^H J3 rt 1 2 >0 r).f<5 i ag{:-2 5" CS fO ^ K - 4 u j e X "f O. O f>-l "^ CS O CS O ) 4 ~ ; H . ^ *^ 5 E SKS'*' J^CN O\ CN *-* K 5 00 0, ^ 00 CNIO.-H ;>-< 00 3 CNCN -H fO HI "- 1 "o VC CNt^ e IH O at^OfC 00 CN **" ^ t>- ^" IO ^ CN 00 X- CNIO CN1O ?P CN X- CN t CNrt CN S 3 W X! ** ^ lilli li Average CNCNCN etus: weight 'Degenerate tuses nearest nerate fetus: t sufficiently v -x- M a 3 o H ,100rH rt 00 i;Q S "16* ^ 1/5 t>> IO CN CS *H Shi" 8 OvCN 2 3 IB'* Ip!l 3 _ oo 10 CNIO OCN N CN CS IggSf 3 -H .S fe* .2 j M O 01 g 5-0 a! 1 Ivs*! 2 "* s j 10 00 C CN IO CS f*5 ^1 CS CN Tf llfll 5 " o ^^ i,5 3 S 3 J &"" 4 j u S * 00 _) 9 4 "^ CN O CN nj M ^ a*-' 01 CNlr-l l|||i 3 IH U ^3^1? 3 (0 CN *x^J !S - iorn ol X-. CN CN *O CN PO 5|ls g .52 Shl-S.' DO *"? o'C J 2 ^^3rt^ O ^ il Ov >O CN ^Jl CN CN ai g 'C D jjj J "* .2 ajS*"" S. 3o,oo -^2 < "So 3 K . . M V . . V . . . 11 476 BULLETIN No. 375 [November, -& ^ M r- f> c^i r^ ^* /> cs oo i** 21 fi-: S=-S-:2- - & ^oo \r> 10 ^'OcsOO c-iOO S 1C O O CS t* O O t>- O *O 00 *O 'OOt* 1 (3 3 C 00 r-1 f*5 f*3 O 00 *- ^ -< *- **i *O O O -< ^O C *-t I-H *-r ,-< H f*5 **5 (S jy m * Tt * '3 o- f J , K ^00-^^00, Tf^^^^O- 6 "= 00 ^H rt CS -H Tt tS CS i-l .w VOT). t-O^Tj. ^00 Tf.Tj.Tf.Ov C o o O ^0* ^ rOTf.0^iOt-OOCOO>CN C n 3 ^ Oc3o/>OTfT^rn 5 1 S Tf. TJ. 0>Ot-OTt.SOTj.Tj,Tj.^Tt^ Tf. > M Sj;g^55:SSggSSSSS J * Date slaughtered 1928 ^ - - tc i 3 2;S^^!SS>S2S?lMIo 1931] FOOD REQUIREMENTS OF PREGNANCY IN SWINE 477 posited for chemical analysis. The data on the fetuses are arranged from left to right in the order in which they occurred, starting at the tip of the right horn of the uterus. The occurrence of partially ab- sorbed or degenerated fetuses is indicated in the body of the table and their weights are recorded in the footnotes. The data obtained from gilts examined in different stages of preg- nancy, including weights of ovaries, have been summarized in Table 4. The uterus and contents just before parturition represent from 8 to 10 percent of the live weight of the gilt. In two nonpregnant gilts weighing 250 and 220 pounds the weights of the uteri were 222 grams and 207 grams respectively, representing .195 and .207 percent of the live weight. The three gilts slaughtered at the end of 16 weeks of gestation gained 122, 121, and 117 pounds from the date of successful mating to the date of slaughter. The products of conception constitute, re- spectively, 29.8, 28.1, and 36.0 percent of the live weight gained during pregnancy. The first gilt was carrying 6 fetuses, the second 7, and the third 10. The weights and lengths of fetuses as measured in this experiment are all greater than those for like ages reported by Warwick, 13 * but whereas in Warwick's data the weight of the fetus first reaches that of the fetal membranes between the sixtieth and seventieth days of the gestation period, in the data given here that relation occurred be- tween the seventieth and the seventy-seventh day of gestation. A more detailed analysis of fetus weights is given in Table 5. The variability in fetus weights, as measured by the coefficient of variation, TABLE 5. AVERAGE WEIGHTS OF MALE AND FEMALE FETUSES AT DIFFERENT AGES, AND THEIR VARIABILITY Gilt No. Week of pregnancy Number of normal fetuses Average weights of Variability in weights of fetuses 1 Male fetuses Female fetuses All fetuses 13 PC 5 6 7 8 9 10 11 12 12 13 14 14 15 16 16 16 9 7 10 6 7 5 12 12 9 11 10 7 9 6 10 7 gms. 16'.S7 37.62 83.09 156.5 292 417 446 472 547 1 043 1 082 1 132 1 597 1 175 1 286 gms. ii!73 35.67 82.96 159.5 218 359 449 451 563 1 041 1 005 1 167 1 504 1 106 1 195 gms. 4.46 15.78 36.65 83.05 158.2 263 388 447 461 558 1 042 1 049 1 160 1 535 1 141 1 234 perct. 18.8 10.2 5.6 6.9 3.9 20.0 12.8 17.9 12.3 11.3 8.6 5.2 9.3 4.7 13.9 10.7 99 PC 26-39 DJ . . . 67-90 PC 3-90 PC 24-90 PC ... 65-90 H 32 DJ 69-30 DJ . . . 13-99 DJ 69-33 DJ 24-9 PC 14-90 DJ 24 PC 39-90 PC 66 PC 1 These percentages are coefficients of variation, that is, standard deviations expressed as per- centages of the corresponding means. 473 BULLETIN No. 375 [Not-ember, decreased rather regularly from 18.8 at 5 weeks of gestation to 3.9 at 9 weeks. Then followed a period of greatly increased variability, the coefficient being 20.0 at 10 weeks, and remaining above 10 for the following 4 weeks, after which smaller coefficients prevailed irregularly up to the end of gestation, at which time two larger coefficients of 13.9 and 10.7 were obtained. The biological significance, if any, of these changes in variability is not evident. The male fetuses averaged heavier in weight than the female fetuses in 11 of the 15 litters in which sex was distinguished. The mean percentage difference between sex averages for .these 15 litters with its probable error was 5.5 1.4. It may be said, therefore, with considerable assurance that, from the sixth to the sixteenth week of gestation at least, male pig fetuses tend to have a greater weight than female fetuses. Among a large number of unselected litters, exhibiting considerable heterogeneity, Carmichael and Rice 1 * have reported only a small advantage in birth weight of male pigs over female pigs ; i.e., 2.59 pounds compared with 2.51 pounds. Concerning the effect of size of litter upon weights of fetuses, there are only three pertinent comparisons ; namely, between the two or more gilts killed at the same stage of gestation at the end of the twelfth, fourteenth, and sixteenth weeks. At the twelfth and four- teenth weeks different-sized litters were obtained, but the average fetus weight, while favoring the smaller litter, was very nearly the same for litters of 12 and 9 and for litters of 10 and 7, respectively. At the sixteenth week the litter from Gilt 24 PC, numbering 6, was heavier per fetus than the other litters of the same age, out of all proportion to differences in size of litter. The difference in average fetus weight between litters from Gilts 39-90 PC and 66 PC favors the smaller litter. Chemical Composition of Samples The chemical composition of total fetuses and membranes and of the uteri, both when containing all the products of conception and after their removal, is given in Tables 6, 7, 8, and 9. The analyses of the fluids removed from the uterus are not in themselves of any signifi- cance, since variable amounts of blood contaminated the amniotic fluids. The results of these analyses, therefore, are not given, altho they have, of course, been used in computing the composition of the uteri plus contents. In the fetus samples the rapid increase in dry matter with increasing age is simply an instance of a phenomenon of general occurrence in growing organisms. To remove the effects of this change upon the variations in the percentage occurrence of the other constituents, the 1931] FOOD REQUIREMENTS OF PREGNANCY IN SWINE 479 (X O* V) O f- *> O^ ^* ^O *^- ^ **5 P^ rs 00 0! liiiiiiiiiiigaii CD U o2Js*^S^siP:o8 c3 oooooooooooooS SB'S < ^ :8googggggggg 8222222222222222 OOOwOOOOOOOOOOO Iz l^OOOONOrt-HrtiN'i'TjivOt^lO'O m a Z x! oZ iO"1>O'*'t'*iOt^t^.o\t^oOOO>Ovrt H M 03 S U t .^^VOCO^O^OOJ-.^NOOO s J s"^ S38838SaS2SKS8SS ^g dl UH ft g O z o J3 < ^^^^^^^^^^c^^^^^W tn 2 is < - "- II 8a3a3KSSSa==2SS8 u u o ll S>S53SSaS3S3SS!3a5!S W * V < s a wg D 5 OS 2o SSSSSSSSSSSSSISES M w OH D 13 g'S )^8S8^)S88$^S5 -- - r-I (I) J ________ 1 O 'w gsssisasMtsiasaa n H d 3MoirtS53SS"2^ HJJ g U W J3 2 * 8 o| 1 SI 1 u bo mall cal rt O 3 s o OZ 1 ->CJUO | -)>-> 1 -> -i- -O ; Q CL, CL, fL, 33 'QQQOQ '0^ (J(J OOOO^O ^oU C I 1 3 d oz 1 w ^(NO CSVO<^>0-HSO 00 00 OOO>O^OOOOOOOvOOOOOO>O *l O'>O'tuT*'l^-iO<^OOWO>fO'Ot^ w* >>> 1 >- > .(J IX, 000000-SSNSSS55^^ CD u ,41 t, siiisiiliiiiilii Cfl u 13 o u oZ H D u ,_, 2 S iO'J'>OiorOM-. r^iovO'noO-*y5 H On 0) 85 sggssgssasss?^^^ H 00 2 .rt^HrtfSfSCSOKSCS o u ** n o^oa-^-^axujo^-r.^ O H wg U U a '5 sssssssssssss^s 1. o^ U& w n E^ 8 &! 882888^8S3SR8S9 3 o ->U -U '->'->>- "-> -U 1931} FOOD REQUIREMENTS OF PREGNANCY IN SWINE 481 w u M I! fc oioio -ovoIoSioKS . M "" ill .^.s^es^oo ^oo,-os* fc -,.3 a* t~iovON000^t^T(.^000 '0 0! 13 c U ^^^SSS^tNSS^SStNScN ii :SS?SS8S :S2snS 'si (S S OOsO^OO^^r>^ 2 ..o^^^^^^^^^^^^.^^ J5 .S^^^^^^OO-OO-HCS^^CSO I! SS^S55S22SS^S^^SS wg S's O^ioaoOO^^tN^rot-tSN^^ 1 *SStt$ZZ**S*SXZS s| 0) 00 o 5 ' -QcupLcpHS :QQQ^Q -cu 482 BULLETIN No. 375 [November, analytical results have been calculated to the dry-matter basis and sum- marized in Table 10. Certain interesting changes are evident from this table. The percentage of fat (ether extract), as well as the gross energy content per gram of dry matter, shows no progressive increase or decrease during the course of intrauterine life. The nitrogen and crude-protein content are also of this description, exhibiting only ir- regular variations, except possibly a decrease in the last few weeks of gestation. The ash content of the fetuses on the dry-matter basis increases from 12 to about 22 percent from the fifth to the eleventh week of gestation, with no further progressive change during the last five weeks of pregnancy. The percentages of calcium and of phos- phorus increase irregularly up to the termination of pregnancy, as do also the percentages of calcium and, less certainly, of phosphorus in the ash. The ratio of calcium to phosphorus increases from a value of 1 to 1.25 at the sixth week, to more than 1 to .60 at the eleventh week, with no clearly progressive change evident from then to parturition. The iron content of the fetuses varied irregularly around an average value of .021 percent of the dry matter. TABLE 11. PERCENTAGE COMPOSITION OF FRESH FETAL LIVERS AND SPLEENS Dry matter Crude protein Ether extract Ash Gross energy 1 Iron Cal- cium Phos- phorus Livers Gilt No. 39-90 PC.. . Gilt No. 66 PC. . . 22.85 21.98 9.81 11 19 1.35 1 06 1.17 1 55 1 147 1 146 .020 .017 .0091 .0091 .211 .251 Spleens Gilt No. 39-90 PC . . 17.34 .014 Gilt No. 66 PC 18.08 .016 'Expressed in small calories per gram. For the purpose of determining to what extent iron was stored up in the fetal liver and the fetal spleen, the livers and spleens of the fetuses from two of the gilts carried to the end of the sixteenth week of pregnancy were removed for separate analyses. The blood draining from these organs after removal was added to the respective fetus sample. The weights of the fetal livers and spleens are given in Table 3. For each of the two litters a composite sample was made for each organ for chemical analysis, the results of which are given in Table 11. The composite spleen sample was so small that it was analyzed only for dry matter and iron. The iron content of the fetal livers and spleen was considerably greater than that of the entire fetus (Table 6), indicating a storage of iron in these organs. But the fetal livers and spleens are not richer in iron than the corresponding organs from adult pigs, judging from the analyses reported by Elvehjem and Peterson. 2 * According to their 1931] FOOD REQUIREMENTS OF PREGNANCY IN SWINE 483 analyses, hog liver, with a dry-matter content of 31.3 percent, contains an average of .025 percent of iron, or on the dry basis .080 percent. The fetal pig livers analyzed in this experiment contained an average of .018 percent of iron on the fresh basis, and .083 percent on the dry basis. Hog spleen, containing 22.1 percent of dry matter, analyzed .029 percent iron on the fresh basis and .133 percent on the dry basis. The fetal spleens of this experiment contained an average of .015 per- cent of iron on the fresh basis and .084 percent on the dry basis. From these comparative figures there is no evidence that the pig at birth is any better fortified against a regime on a low-iron diet than is the adult pig. It is interesting to note with reference to the analyses of the fetal livers that the sum of the crude protein, ether extract, and ash percent- ages is considerably smaller than the percentage of dry substance. In one litter of fetuses the undetermined dry matter is equivalent to 46.0 percent of the total dry matter, while in the other litter it accounts for 37.2 percent. These figures suggest a high content of glycogen in fetal livers, but Mendel and Leavenworth 10 * were unable to detect even traces of glycogen in the livers of pig fetuses as old as approximately 90 days. There is, of course, a possibility that in the last three weeks of intrauterine life glycogen accumulates in high concentration in the livers of pig fetuses. The low percentages of ether extract in these livers, 1.35 and 1.06, indicate that the pig, unlike the guinea pig, does not store any considerable amount of fat in the liver during intra- uterine life. According to Imrie and Graham, 6 * the guinea-pig fetus accumulates large amounts of fat in its liver during the latter part of intrauterine life, a storage which is rapidly depleted soon after birth. Mathematical Analysis of Chemical Data The primary purpose of this investigation was to measure the rate of deposition of nutrients in the uterus of the pregnant gilt thruout the period of fetal growth. The data actually obtained, however, by the chemical analysis of the uterus and contents of gilts sacrificed in groups of one to three at weekly intervals from the fifth to the six- teenth weeks of pregnancy, do not give directly any connected picture of fetal growth or of the growth of the total products of conception. The gaps in the picture are too large and the irregularities in the data too extreme to afford anything but a rough idea of the processes under study. Much more difficult would be the task of obtaining consistent and significant measures of the rates of growth with respect to different nutrients from the "raw" data as it came from the laboratory. Obviously the occasion calls for a mathematical analysis of the 484 BULLETIN No. 375 [November, H O O U o ' II U Q Z I M ^SSgg^SSSSSSSSSBS o 0*0 '-"" H Weight of 11 rl< (v) O n t- O <2rOiOMnTj.OOO,rl. - '8SSSSSS82R lSiSS88R3|=g55| 3 ^ts-a^t -.OaOt-oD (NOt^tvO mio _ ^ ^ CS - 1 -* -U . Q Cu cu cu SC -QQQ^Q Pi 1931] FOOD REQUIREMENTS OF PREGNANCY IN SWINE 485 data in order to fill in the gaps in the most satisfactory manner and to remove those irregularities in the data that result from random sampling and environmental disturbances rather than from inherent changes with age of the growth processes themselves. The first step in this analysis was to compute, from the weight and composition of the various samples, the total contents of the uteri in the various chemical constituents. The results of this computation are given in Table 12. Not all these weights of constituents, however, are products of conception, since they include the materials that would have been present in the nonpregnant uterus. Estimates must, therefore, be made of these constituents. In three nonpregnant gilts the weight of uterus was found to equal 88.8, 94.1, and 74.2 grams per 100 pounds body weight, with an average of 85.7 grams. Chemical analysis of these uteri gave the following average percentage composition: dry matter 21.94, crude protein 15.50, ether extract 5.36, ash 1.07, total nitrogen 2.48, iron .00201, calcium .0116, phosphorus .134, and gross energy 1,367 small calories per gram. Furthermore, the number of normal fetuses found in the uteri of these gilts varied from 5 to 12, averaging 8.56, and much of the varia- tion in weights of constituents among successive gilts was due to this fact. Hence it seems necessary to correct such weights to some stand- ard litter size. All weights of constituents, after deduction of the estimated constituents in the nonpregnant uterus, were therefore cor- rected to a litter size of 8 by direct ratio. Thus in a litter of 6 all weights were increased by a third, and in a litter of 10 they were de- creased by a fifth. It is admitted that this correction is only partially justifiable, but information does not seem to be at hand to make the correction on a more satisfactory basis. In particular, the weights of constituents in larger litters should not be reduced as much as the ratio of 8 to their litter number, since larger litters are associated with smaller fetus weights ; and conversely, the weights from smaller litters should not be increased as much as they are by the method used. In the absence, however, of any definite knowledge of the regression of fetus weight on litter size at different stages of gestation no other method of correction seemed available. It is not believed that the errors committed by this correction method are large. Thus from Table 3 it appears that for the two gilts sacrificed after 12 weeks of pregnancy, the average fetus weight for the litter of 9 was 461 grams, and for the litter of 12, almost as much, 447 grams. For the two gilts slaughtered after 14 weeks of pregnancy the average fetus weight for the litter of 7 was 1,049 grams, and for 486 BULLETIN No. 375 [November, the litter of 10 was 1,042 grams. For the three gilts killed after 16 weeks of pregnancy the average fetus weight was 1,535 grams for the litter of 6, 1,234 grams for the litter of 7, and 1,141 grams for the litter of 10. At birth, according to Carmichael and Rice, 1 * there is no great difference between weights of pigs in large and in small litters. From a survey of 549 litters, averaging 8.1 pigs per litter, they found the average birth weight in all litters with fewer pigs than the average to be 2.67 pounds, and that with more pigs than the average, 2.47 pounds. In Table 13 these corrections have been made with reference to fresh weight of the products of conception ; weights of crude protein, ash, calcium, phosphorus, and iron; and calories of gross energy. These are the data of significance to the problem of the nutritive re- quirements for reproduction in swine. Before attempting to describe these several groups of data by appro- priate mathematical expressions, it is of interest to inquire what fraction of the nutrients contained in the total products of conception are found in the fetuses themselves at different stages of gestation. This infor- mation is given in Table 14. The percentages with respect to each of the constituents increase with the progress of gestation, but this in- crease is much faster with respect to some constituents than with re- spect to others. For ash, calcium, and phosphorus the fetuses account for 85 to 95 or more percent of the total at parturition, and for more than 70 percent of the dry matter and the gross energy. In fresh weight and in iron, however, the fetuses, even at parturition, account for only slightly more than half the total, due to the presence of the amniotic fluids in the uterus and evidently to the fact that a dispropor- tionate share of the blood was present in the nonfetal parts. The mathematical equation fitted to the data of Table 13 is one that has been successfully used in describing intrauterine growth in a number of species of animals; 8 ' 11 - 12 * namely, W=kt n , W being, in this case, the weight of the nutrient deposited in the uterus at the end of gestation week t, while k and are constants' to be determined from each set of data. The constants were determined by the method of least squares. The resulting equations are as follows: (a) Total fresh weight of products of conception: W = 99.05 f 1 - 886 (b) Total gross energy: W = 4.077? 2 - 841 (c) Total crude protein: W = 1.523* 2 - 482 (d) Total ash: W= .06166/ 3 - 176 (e) Calcium: W = .0001940/ 4 - 748 (f) Phosphorus: W = .002167/ 3 - 690 (h) Iron: W= .8174f 2 - 368 In the case of iron, W is the weight in milligrams rather than in grams. FOOD REQUIREMENTS OF PREGNANCY IN SWINE 487 XB .ssssssssssssssss ^ *8 - N, W <>. 00 000 ro c O g o ^ (Niof^tNio^^^f;-- oc o (N ^t r: 10 5 (d O U 3 C O J3 . Tf ^CS ^*OC r~N_ | O 2 ^. ^*^(*5OOOO r *5^f > 'O' v 10C^^f^O H O (N fS Tt Ov CN IO 00 ,*,*,<,-,_ H Ed S- . oo < 10 1^ oo ^ ** - fo o o> >o -* f> cs (d "*"_ej |^***^*^**3*<$8 3 H " Id in D |l -2 ^-20, td tin en H Id iy g NSTITU I U Id CO Gilt No. H 00 I a 1 Calcium ^ j: ** oo u U Jfl < Ether extract =, *~-~ : -SI - 2 o $ P| Fresh substance 2SSSSSS555583S Jd S U OC 6 oz * " Q Cu ft< Cu 2C 'QQQ^Q CJ CJ ^ ^ ^ ^*. U /"-s O 2;SS^SSS2SS2:SS5S 483 BULLETIN No. 375 [November, 20000 O 16000 12000 eooo 400O 6 8 IO WEEK OF GESTATION FIG. 1. FRESH WEIGHT OF TOTAL PRODUCTS OF CONCEPTION AT DIFFERENT STAGES OF GESTATION The fit of these equations to their respective sets of data is shown in Figs. 1 to 7. The total products of conception, fresh weight, showed such a variable and irregular increase that no simple mathe- matical expression could be fitted to them satisfactorily. The equation used does, however, possess the merit of passing thru the data in such a way that the deviations from points below the curve almost balance 2000 a 1600 Z i z * / UJ 5 1200 5. a. 1 / t \ / OF CRUDE 0> 8 S 7 1 $ 400 < 4 _x s^ ( 1 ' _ ^ > ; ' - J ^ K^ ! 4 6 8 10 12 14 16 WEEK OF GESTATION FIG. 2. DEPOSITION OF CRUDE PROTEIN AT DIFFERENT STAGES OF GESTATION 1931} FOOD REQUIREMENTS OF PREGNANCY IN SWINE 489 12000 10000 8000 6000 4000 7 2000 6 8 10 12 14 16 WEEK OF GESTATION FIG. 3. GROSS ENERGY CONTENT OF MATERIAL DEPOSITED AT DIFFERENT STAGES OF GESTATION 600 5OO 400 i i i ; / / 100 y, / > r^ ^^ X 2 4 6 8 10 12 14 16 WEEK OF GESTATION FIG. 4. DEPOSITION OF TOTAL ASH AT DIFFERENT STAGES OF GESTATION 490 BULLETIN No. 375 [November, WEIGHT OF CALCIUM IN GRAMS to & o> 0) o to o o o o o o o < / I 1 I :/ / 1 Q ^ ' ^^^^\ \ 2 4 6 8 10 12 14 16 WEEK OF GESTATION FIG. 5. DEPOSITION OF TOTAL CALCIUM AT DIFFERENT STAGES OF GESTATION J 60 50 < 140 :30 7L7- 24 6 8 10 12 14 16 WEEK OF GESTATION FIG. 6. DEPOSITION OF TOTAL PHOSPHORUS AT DIFFERENT STAGES OF GESTATION 1931} FOOD REQUIREMENTS OF PREGNANCY IN SWINE 491 948- 5400 5 200 6 8 10 12 14 16 WEEK OF GESTATION FIG. 7. DEPOSITION OF TOTAL IRON AT DIFFERENT STAGES OF GESTATION the deviations from points above the curve. For the other sets of data the agreement between the curves and the observations is much better, particularly up to and including the data for the eleventh week of gestation. Beyond this point considerable irregularity exists with all sets of data, but in all cases the curves pass thru the data as centrally as a simple curve can. TABLE 15.- -CoMPUTED WEIGHTS, ENERGY CONTENTS, AND COMPOSITION OF THE TOTAL PRODUCTS OF CONCEPTION FOR A LITTER OF EIGHT Week of gestation Total fresh weight Crude protein Gross energy Ash Calcium Phos- phorus Iron 1... gms. 99 gms. 1.5 cols. 4.1 gms. .06 gms. .0002 grits. .002 mgms. .82 2 366 8 5 29 6 .005 .028 4 2 3 787 23 92 2 .036 .12 11 4 1 354 47 209 5 .14 .36 22 5 2 062 83 394 10 .40 .82 37 6 2 909 130 662 18 .96 1.61 57 7 3 891 191 1 026 30 2.0 2.8 82 8 5 005 265 1 499 45 3.8 4.7 113 9 6 251 356 2 094 66 6.6 7.2 149 10 7 625 462 2 825 92 10 9 10 6 191 11 9 127 585 3 703 125 17 1 15.1 239 12 10 755 726 4 742 165 26 21 294 13 12 507 886 5 952 213 38 28 355 14 14 385 1 065 7 347 269 54 37 423 15 16 384 1 263 8 938 335 74 47 499 16 :.... 18 505 1 483 10 736 411 101 60 581 492 BULLETIN No. 375 [November, From the fitted equations values for the weights of the various constituents deposited in the uterus at any stage of gestation may be computed. Such values for weekly intervals are contained in Table 15. These "smoothed" data may be considered more significant than the "raw" data contained in Table 13. Certainly they present a more plausible and consistent picture of the deposition of nutrients in the pregnant uterus, since each individual value is determined by the gen- eral trend of the data for all gilts examined rather than by the data obtained from one, two, or three gilts, any one of which may be affected to a considerable extent by a number of conditions with refer- ence to individual behavior not representative of the particular stage of gestation at which they were sacrificed. Another important advantage of a concise description of these data by means of mathematical equations, is that the rate of deposition of the nutrients in the uterus may be readily obtained by differentiation of the equations and solution for any desired value of t. Differentia- tion of the equation W = kt n , yields the equation - - = nkt n ~ 1 dt dW . in which - - is the instantaneous rate at which the nutrient in ques- dt tion, W, is being deposited at any week of gestation, /, expressed, in these cases, in grams, milligrams, or calories per week. The differential equations obtained for the fresh weight of the products of conception and for the various nutrients, expressed for convenience in the loga- rithmic form, are as follows: /dW\ (a) Total fresh weight of products of conception: log I - - 1 = \dt / 2.27 150 +.88637 log t (b) Total gross energy: log ( )= 1.06368 + 1.84066 log t \ dt / (c) Total crude protein: log ( )= .57760 + 1.48171 log t \ dt / (d) Total ash: log (^?)= -.70811 + 2.17588 log t / 7 ' (e) Calcium: log( - - ) -3.03558 + 3.74793 log t \ dt / . ( f ) Phosphorus: log (^-] = -2.09712 + 2.69047 log t (h) Iron: log ( - - .28689 + 1.36831 log t. dt / 1931} FOOD REQUIREMENTS OF PREGNANCY IN SWINE 493 TABLE 16. COMPUTED DAILY RATE OF INCREASE IN WEIGHT AND ENERGY CONTENT, AND COMPUTED DAILY DEPOSITION OF NUTRIENTS IN THE UTERI OF PREGNANT GILTS Week of gestation Total weight Crude protein Gross energy Ash Calcium Phos- phorus Iron 1 gms. 27 gms. .54 cols. 1 6 gms. .028 gms. 0001 gms. 0011 mgms. 28 2.. . 49 1 5 5 9 126 0018 0074 71 3 71 2 7 12 5 30 0081 022 1 24 4 91 4.2 21 .57 024 048 1 84 5 111 5.9 32 .93 .055 .087 2 50 6 131 7 7 45 1 38 109 142 3 2 7 150 9.6 59 1.93 194 215 4 8 169 11.8 76 2.6 .32 .31 4 8 9 187 14 94 3 3 50 42 5 6 10 205 16 115 4.3 74 56 6 5 11 224 19 137 5.2 1.05 .72 7.4 12 242 21 160 6.2 1.46 .91 8.3 13 259 24 186 7.4 1 97 1 13 9 2 14 277 27 213 8.7 2 60 1.38 10.2 15 294 30 242 10 1 3 37 1 67 11 2 16 312 33 272 11.7 4.29 1.98 12.3 By solving for any value of t, the time in weeks from conception, the corresponding rates of deposition of the materials may be obtained. In Table 16 will be found the results of such calculations for the end of successive weeks of gestation, expressed in grams, milligrams, or calories per day rather than week. Thus at the end of the sixteenth week of gestation a pregnant gilt carrying an average litter of 8 is depositing in the uterus daily 312 grams of fresh material having an energy content of 272 calories and containing 33 grams of crude pro- tein, 11.7 grams of ash constituents, 4.29 grams of calcium, 1.98 grams of phosphorus, and 12.3 milligrams of iron. At the termination of the y 6 6 10 WEEK OF GESTATION FIG. 8. DAILY RATE OF DEPOSITION OF CALCIUM AND OF PHOSPHORUS AT DIFFERENT STAGES OF GESTATION 494 BULLETIN No. 375 [November, tenth week of gestation the rates of deposition of the various nutrients are one-half or less the rates just specified. The rapid increase in the rate of deposition of calcium is par- ticularly noteworthy. In the last three weeks of gestation the daily increase of calcium more than doubles. The rate of deposition of phosphorus also increases rapidly, but not nearly so rapidly as that of calcium. Fig. 8 compares the rates of deposition of these two ele- ments for the entire sixteen weeks of gestation. These rates of deposition measure the minimum daily requirements of the nutrients for reproduction. They are the final calculations towards which all the chemical work was directed; hence they are considered to be the most significant results of the entire investigation. Nitrogen, Calcium, and Phosphorus Balances of Pregnant Gilts Five of the pregnant gilts serving as subjects in this experiment were confined continuously in metabolism crates in the nutrition labora- tory until the time of slaughter. Except for occasional short intervals of time, generally no more than two or three days, continuous balances of nitrogen, calcium, and phosphorus were obtained for these gilts in consecutive 10-day collection periods. For four of the gilts one or more collection periods were undertaken before the date of successful breeding. The balance sheets for all periods, containing the detailed data for intake, excretion, and storage of these elements, are given in Table 17. The balances of these elements only have been summarized for chronological comparison in Table 18. A noteworthy feature of these nutritive balances as gestation pro- gressed is that there is no tendency for an increase in storage, altho the demands of fetal growth are increasing, particularly in the last few weeks. In fact, with respect to phosphorus, there is a distinct tendency for the balances to decrease during the first half of the gestation period. Evans 3 * also has noted no correspondence in the nutritive balances of nitrogen, phosphorus, and calcium and the demands for fetal growth in pregnant sows. The average daily retentions of nitrogen, calcium, and phosphorus for each of the five gilts are given in Table 19. Thruout pregnancy there was an average daily storage of 7.12 grams of nitrogen, 4.38 grams of calcium, and 1.32 grams of phosphorus, representing 17.8, 31.5, and 16.0 percent, respectively, of the daily intakes of these ele- ments. On a much more liberal regime of feeding Evans 3 * secured with sows of considerably greater weight average daily balances of 12.51 grams of nitrogen, 4.58 grams of calcium, and 2.75 grams of phosphorus during pregnancy. 1931} FOOD REQUIREMENTS OF PREGNANCY IN SWINE 495 It is of interest to compare the total amounts of nitrogen, calcium, and phosphorus retained thruout the pregnancies of these gilts with the amounts deposited in the uterus. The former amounts were com- puted from the metabolism data, due allowance being made for the intermittent short periods of time for which collections were not made ; the latter amounts were determined by actual analysis of the uterus and contents of each gilt, allowance being made for the nutrients con- TABLE 17. BALANCE DATA OF PREGNANT GILTS (Results expressed on the daily basis) Inclusive dates of metabolism periods Nitrogen Calcium Phosphorus Body weight at start of period Gilt 39-90 PC, bred February 21, 1928 January 19 to 25 Intake gms. 47.63 gms. 16.55 gms. 9.80 Ibs. 298 Output 32.80 8.15 6.19 + 14.83 +8.40 +3.61 January 26 to 31 Intake 47.63 16.55 9.80 303 Output 37.11 9.52 7.96 + 10.52 +7.03 +1.84 February 23 to 29 Intake 39.69 13.79 8.16 331 Output 30.57 7.08 5.41 +9.12 +6.71 +2.75 March 1 to 10 Intake 39.69 13.79 8.16 340 Output .... 33.54 9.51 7.55 Balance +6.15 +4.28 + .61 March 14 to 23 Intake . f 39.69 13.79 8.16 355 Output 32.78 10.48 7.69 Balance +6.91 +3.31 + .47 March 24 to April 2 Intake 39.69 13.79 8.16 365 Output 32.97 9.66 6.62 Balance ... . +6.72 +4.13 +1.54 April 3 to 12 Intake 39.69 13.79 8.16 376 Output. . . . 37.91 10.74 7.06 Balance + 1.78 +3.05 + 1.10 April 13 to 22 Intake 39.69 13.79 8.16 387 Output 33.21 10.34 7.39 Balance +6.48 +3.45 + -77 April 27 to May 6 Intake 39.69 13.79 8.16 409 Output. 29.67 8.56 5.66 Balance + 10.02 +5.23 +2.50 May 7 to 16 Intake Output 39.69 31 .94 13.79 9.82 8.16 5.42 418 Balance +7.75 +3.97 +2.74 May 17 to 26 Intake . . . 39.69 13.79 8.16 422 Output 34.18 10.35 6.96 Balance +5.51 +3.44 + 1.20 May 27 to June 5 Intake 39.69 13.79 8.16 432 Output 34.40 8.07 6.69 Balance +5.29 +5.72 +1.47 June 6 to 1 1 Intake Output 39.69 34.98 13.79 10.54 8.16 8.51 445 Balance +4.71 +3.25 -.35 Note. The line between the second and third periods indicates the location of the breeding date. (This table is continued over the next four pages.) 496 BULLETIN No. 375 [November, tained in the nonpregnant uterus. The results of such calculations are summarized in Table 20. For all gilts the storage of nitrogen, calcium, and phosphorus dur- ing pregnancy was greatly in excess of the amounts of nutrients ac- tually used in fetal growth. On the average, only 31 percent of the nitrogen stored in the bodies of these gilts during pregnancy was used for the growth of the fetus, its membranes and fluids, and for the hypertrophy of the uterus ; only 20 percent of the calcium stored was TABLE 17. Continued Inclusive dates of metaboli ;m periods Nitrogen Calcium Phosphorus Body weight at start of period Gilt 24 PC, bred February 1, 1928 January 16 to 22 Intake gms. 47.63 gms. 16.55 gms. 9.80 Ibs. 251 Output 33.19 8.57 5.91 + 14.44 + 7.98 +3 89 January 23 to 29 Intake 47.63 16.55 9.80 259 Output 34.01 9.07 6.65 + 13.62 +7 48 +3 15 February 1 1 to 1 7 Intake 47.63 16.55 9.80 278 Output 34.68 8.73 6.80 + 12 95 + 7.82 +3.00 February 21 to 27 Intake 39.69 13.79 8.16 291 Output 28.79 8.29 5.77 Balance + 10.90 +5.50 +2.39 February 28 to March 5 39.69 13.79 8.16 302 Output 36.82 12.93 8.98 Balance +2.87 + .86 .82 March 6 to IS Intake Output 39.69 31.32 13.79 9.81 8.16 7.55 310 +8.37 +3.98 + .61 March 16 to 25 Intake 39.69 13.79 8.16 319 Output 33.59 10.05 7.00 Balance +6.10 +3.74 + 1.16 March 26 to April 4 Intake Output 39.69 34.36 13.79 11.44 8.16 7.13 326 +5.33 +2.35 + 1.03 April 5 to 14 39.69 13.79 8.16 Output 33.46 10.96 8.22 Balance +6.23 +2.83 -.06 April 15 to 24 Intake 39.69 13.79 8.16 351 Output 30.17 10.80 7.17 Balance +9.52 +2.99 + .99 April 27 to May 6 Intake Output 39.69 29.67 13.79 9.21 8.16 6.17 369 + 10.02 +4.58 + 1.99 May 7 to 16 Intake 39.69 13.79 8.16 375 Output 34.44 9.38 6.21 Balance +5.25 +4.41 + 1.95 May 17 to 22 39 69 13.79 8.16 383 Output 29.56 9.81 6.68 Balance + 10.13 +3.98 + 1.48 Note. The line between the second and third periods indicates the location of the breeding date. 1931] FOOD REQUIREMENTS OF PREGNANCY IN SWINE 497 so used, and 40 percent of the phosphorus. These gilts were still grow- ing at a rate sufficiently rapid to require 69 percent of all the nitrogen stored, 80 percent of all the calcium stored, and 60 percent of all the phosphorus stored. TABLE 17. Continued Inclusive dates of metabolism periods Nitrogen Calcium Phosphorus Body weight at start of period Gilt 66 PC, bred March 12, 1928 January 18 to 24 Intake gms. 47.63 gms. 16.55 gms. 9.80 Ibs. 266 Output 35.57 7.62 5.73 +12.06 +8.93 +4 07 March 14 to 23 Intake 39.69 13.79 8.16 319 Output 34.39 8.70 6.74 +5.30 +5.09 +1.42 March 26 to April 4 Intake 39.69 13.79 8.16 327 Output 35.04 11.25 7.81 Balance +4.65 +2.54 + .35 April 5 to 14 Intake 39.69 13.79 8.16 337 Output 33.21 10.71 8.12 Balance +6.48 +3.08 + .04 April 15 to 24 Intake 39.69 13.79 8.16 350 Output 33.96 10.64 7.53 Balance +5.73 +3.14 + .63 April 27 to May 6 Intake 39.69 13 79 8 16 360 Output 33.29 11.27 7.19 Balance +6.40 +2.52 + .97 May 7 to 16 Intake Output 39.69 30.99 13.79 10.09 8.16 6.41 372 +8 70 +3 70 + 1.75 May 17 to 26 Intake Output 39.69 34.65 13.79 11.14 8.16 7.65 386 Balance +5.04 +2.65 + .51 May 27 to June 5 Intake Output 39.69 34.64 13.79 10.13 8.16 7.92 397 Balance +5.05 +3.66 + .24 June 6 to 15 Intake 39 69 13 79 8.16 409 Output 32.42 6.61 Balance +7.27 + 7.18 June 16 to 25 Intake 39.69 13.79 8.16 414 Output 27.76 6.34 5.66 Balance + 11.93 +7.45 +2.50 June 26 to July 1 Intake 39.69 13.79 8.16 431 Output 27.80 7.67 5.86 Balance +11.89 +6.12 +2.30 Note. The line between the first and second periods indicates the location of breeding date. 498 BULLETIN No. 375 [November, TABLE 17. Continued Inclusive dates of metabolism periods Nitrogen Calcium Phosphorus Body weight at start of period Gilt 69-33 DJ, bred January 30, 1928 Intake gms. 47.63 gms. 16.55 gms. 9.80 Ibs. 298 Output 31.42 6.15 5.14 +16.21 + 10.40 +4 66 January 24 to 29 47.63 16.55 9.80 308 Output 38.80 8.65 6.93 +8 83 +7.90 +2 87 February 3 to 9 Intake 47.63 16.55 9.80 314 Output 36.02 8.94 6.58 +11.61 +7.51 +3.22 February 20 to 26 39.69 13.79 8.16 338 Output 31.81 7.12 5.55 Balance + 7.88 +6.67 +2.61 February 27 to March 4 Intake 39.69 13.79 8.16 352 Output 29.55 6.87 5.31 +10. 14 +6.92 +2.85 March S to 14 Intake 39.69 13.79 8.16 353 Output 33.73 9.47 8.29 Balance +5.96 +4.32 -.13 March 15 to 24 Intake 39.69 13.79 8.16 364 Output 32.67 8.71 6.77 Balance + 7.02 +5.08 + 1.39 March 25 to April 3 Intake 39.69 13.79 8.16 378 Output 33.49 9.71 6.95 +6.20 +4.08 + 1.21 April 4 to 13 Intake . . . 39.69 13.79 8.16 395 Output 32.31 8.78 6.38 Balance + 7.38 +5.01 + 1.78 April 14 to 23 Intake 39.69 13.79 8.16 404 Output 32.96 9.20 6.93 +6.73 +4.59 +1.23 April 27 to May 6 39.69 13.79 8.16 421 Output 33.24 9.54 7.14 Balance +6.45 +4.25 +1.02 Note. The line between the second and third periods indicates the location of the breeding date. 1931] FOOD REQUIREMENTS OF PREGNANCY IN SWINE 499 TABLE 17. Concluded Inclusive dates of metabolism periods Nitrogen Calcium Phosphorus Body weight at start of period Gilt 14-90 DJ, bred January 31, 1928 February 20 to 26 Intake gms. 39.69 gms. 13.79 gms. 8.16 Ibs. 320 Output 30.64 7.68 5 84 'Balance +8.95 +6.11 +2.32 February 27 to March 4 . . Intake 39.69 13.79 8.16 330 Output 36.32 11.27 8.64 +3.37 +2 52 48 March 5 to 14 Intake 39.69 13 79 8 16 332 Output.. ..... 36.92 10.56 8 43 Balance +2.77 +3.23 .27 March IS to 24 Intake 39.69 13.79 8.16 340 Output 33.55 9.02 6.52 +6 14 +4 77 +1 64 March 25 to April 3 Intake 39 69 13 79 8 16 348 Output 35.27 10 42 6.95 Balance +4.42 +3.37 + 1.21 April 4 to 13 Intake 39.69 13 79 8 16 362 Output 32.01 9.59 6.79 Balance +7.68 +3.20 +1.37 April 14 to 23 Intake 39.69 13 79 8.16 377 Output 32.61 10.91 7.66 Balance + 7.08 +2.88 + .50 April 27 to May 6 Intake 39.69 13.79 8.16 391 Output 30.28 8.54 5.74 Balance +9.41 +5.25 +2.32 May 7 to 13 39 69 13 79 8 16 394 Output 32 11 8 47 5 52 Balance +7.58 +5.32 +2.64 500 BULLETIN No. 375 [November, u fc" u en U ~ Z< rj < E <, i n u f> f<5 Ov * * t O5 CS 00 u -' ^ .Ml t^^UT^ tO * > < t-^H O oooo -d oo Q . .__ BO lOOul O <"J Ov 5i-l/5 [S tS " + 1 +++ + +++I 1 + ++++ 1 + + 1 +++ + o, : :QQ 2 1931} FOOD REQUIREMENTS OF PREGNANCY IN SWINE 501 TABLE 19. AVERAGE DAILY RETENTION OF NITROGEN, CALCIUM, AND PHOSPHORUS DURING GESTATION cat NO. Absolute retention Percentage 1 retention Nitrogen Calcium Phosphorus Nitrogen Calcium Phosphorus 39-90 PC gms. 6.40 7.97 7.13 7.71 6.38 7.12 gms. 4.23 3.91 4.28 5.38 4.08 4.38 gms. 1.34 1.25 1.07 1.69 1.25 1.32 16.1 19.7 18.0 19.0 16.1 17.8 30.7 27.8 31.0 38.2 29.6 31.5 16.4 15.0 13.1 20.3 15.3 16.0 24 PC 66 PC 69-33 DJ 14-90 DJ Average Computed on the intake. TABLE 20. COMPARISON OF TOTAL AMOUNTS OF NITROGEN, CALCIUM, AND PHOS PHORUS RETAINED DURING PREGNANCY WITH AMOUNTS DEPOSITED IN UTERUS Gilt No. Number of weeks of pregnancy Nitrogen Calcium Phos- phorus 69-33 DJ 14 15 16 16 16 Total retained, grams 768 245 32 724 258 36 941 234 25 729 254 35 768 216 28 535 83 16 463 111 24 478 91 19 474 117 25 470 79 17 172 54 31 153 71 46 159 54 34 155 65 42 118 55 47 14-90 DJ Percent in uterus Total retained, grams 24 PC In uterus, grams Percent in uterus Total retained, grams 39-90 PC In uterus, grams Percent in uterus Total retained, grams 66 PC In uterus, grams. Percent in uterus Total retained, grams In uterus, grams. Percent in uterus Average percentages of balances retained in uterus 31 20 40 SUMMARY For the purpose of determining the minimum nutritive requirements for reproduction in swine, as measured by the rates of deposition of nutrients in the uterus, sixteen pregnant gilts were slaughtered at dif- ferent stages of pregnancy, starting at the end of the fifth week, and the uteri and contents weighed, dissected, and subjected to chemical analysis. Five of the gilts were confined in metabolism crates for 14 to 16 weeks of pregnancy and their balances of nitrogen, calcium, and phosphorus were determined in consecutive 10-day periods. All gilts were bred to the same boar of the Poland China breed, and they were all fed the same ration in amounts to produce an average daily gain of 1 to 1.25 pounds. While the gilts fed in one lot at the swine barn required an average daily intake of 8 pounds of feed, those confined in metabolism crates in the nutrition laboratory required only ^pounds of feed daily. The much greater economy of gains in these 502 BULLETIN No. 375 [November, latter gilts than in the group-fed gilts must have been the result of close confinement, with correspondingly less activity, and possibly to some extent the result of a higher environmental temperature. The digestibility of the ration and its content of metabolizable energy were determined, using the 5 gilts confined to metabolism crates. An average of 77.4 percent of the gross energy of the ration was found to be metabolizable. For the three gilts slaughtered just previous to the time of normal parturition, that is, after 16 weeks of gestation, the total products of conception in the uterus accounted for 29.8, 28.1, and 36.0 percent of the live weight gained during pregnancy. The first gilt was carrying 6 fetuses, the second 7, and the third 10. The variability in fetus weights within the same litter, as measured by the coefficient of variation, decreased rather regularly from 18.8 at 5 weeks of gestation to 3.9 at 9 weeks. Then followed a period of greatly increased variability, the coefficient being 20 at 10 weeks, and remaining above 10 for the following 4 weeks, after which smaller coefficients prevailed irregularly up to the end of gestation, at which time two larger coefficients of 13.9 and 10.7 were obtained. The male fetuses averaged heavier in weight than the female fetuses in 11 of the 15 litters in which sex was determined. The mean percentage difference between sex averages for these 15 litters was 5.5 1.4. It may be said, therefore, with considerable assurance that, from the sixth to the sixteenth weeks of gestation at least, male pig fetuses tend to have a greater weight than female fetuses. The chemical analysis of the fetus samples showed a progressively increasing percentage of dry matter as fetal age increased. On the dry-matter basis certain interesting changes in the composition of the fetuses were noted, particularly with reference to the total ash, calcium, and phosphorus. Neither the percentage of fat nor of iron showed any progressive variation with advancing pregnancy. Altho the iron content of the livers and spleens taken from fetuses close to term was greater than that of the entire fetuses, indicating a storage of iron in these organs, it was not greater than published analyses of the iron content of livers and spleens from adult pigs. For the purpose of a more thoro and complete description and in- terpretation, the chemical data with reference to the amounts of nu- trients contained in the total products of conception at succeeding stages of gestation were, after correction to a uniform litter size of eight, fitted to the mathematical equation W = kt n , in which W is the weight of a given constituent deposited at time t in the uterus. From these fitted equations values for the weights of the various 1931] FOOD REQUIREMENTS OF PREGNANCY IN SWINE 503 constituents deposited in the uterus at any stage of gestation may be computed. Such computed values for weekly intervals are summarized in Table 15. These "smoothed data" may be considered more signifi- cant than the "raw" data as actually determined. Certainly they pre- sent a more plausible and consistent chemical picture of the course of pregnancy. By the differentiation of these equations other equations may be obtained of the type = nkt n ~ 1 , from which the rate of deposition dt of the nutrients, , may be computed for any time t. By solving dt these equations for any value of t, the time in weeks from conception, the corresponding rates of deposition may be obtained. The results of such calculations for the ends of successive weeks of gestation, ex- pressed in grams, milligrams, or calories per day are given in Table 16. At the termination of the sixteenth week of pregnancy a pregnant gilt carrying an average litter of eight may be expected to deposit in the uterus daily 312 grams of fresh material, having a gross energy content of 272 calories and containing 33 grams of crude protein, 11.7 grams of ash constituents, 4.29 grams of calcium, 1.98 grams of phos- phorus, and 12.3 milligrams of iron. At the termination of the tenth week of gestation the rates of deposition of the various nutrients are only one-half or less of the rates just cited. These rates of deposition of nutrients measure the minimum daily requirements of the nutrients for reproduction. They are the final calculations towards which all the chemical work was directed, and hence they are considered to be the most significant results of the entire investigation. From the results of the balance experiments on five of the sixteen gilts it appeared that the gilts were storing nutritive material in their bodies at a much faster rate than they were depositing such material in the uterus, because they were themselves growing. The average daily retentions of nitrogen, calcium, and phosphorus thruout ges- tation were, respectively, 7.12, 4.38, and 1.32 grams, representing 17.8, 31.5 and 16.0 percent of the intakes of the respective nutrients. However, only 31 percent of the nitrogen stored, 20 percent of the calcium stored, and 40 percent of the phosphorus stored was used in the processes of reproduction, the remainder providing material for the growth of the gilts themselves. No tendency was evident for the retention of nutrients in the body to increase as pregnancy progressed. 504 BULLETIN No. 375 [November, LITERATURE CITED 1. CARMICHAEL, W. J., and RICE, J. B. Variations in farrow: with special ref- erence to the birth weight of pigs. 111. Agr. Exp. Sta. Bui. 226. 1920. 2. ELVEHJEM, C. A., and PETERSON, W. H. The iron content of animal tissues. Jour. Biol. Chem. 74, 433. 1927. 3. EVANS, R. E. Protein and mineral metabolism in pregnant sows on a nor- mal or high-calcium diet compared with a calcium-deficient diet. Jour. Agr. Sci. 19, 752. 1929. 4. HAECKER, T. L. Investigations in milk-production. Minn. Agr. Exp. Sta. Bui. 140. 1914. 5. HAWK, P. B. Practical physiological chemistry. P. Blakiston's Son & Co., Philadelphia, 8th ed., 580. 1923. 6. IMRIE, C. G., and GRAHAM, S. G. The fat content of embryonic livers. Jour. Biol. Chem. 44, 243. 1920. 7. KENNEDY, R. P. The quantitative determination of iron in tissues. Jour. Biol. Chem. 74, 385. 1927. 8. MACDOWELL, E. C., and ALLEN, E. Weight of mouse embryos 10-18 days after conception, a logarithmic function of embryo age. Soc. Expt. Biol. and Med. Proc. 24, 672. 1927. 9. McCRUDDEN, F. H. The quantitative separation of calcium and magnesium in the presence of phosphates and small amounts of iron devised espe- cially for the analysis of foods, urine and feces. Jour. Biol. Chem. 7, 83. 1910. 10. MENDEL, L. B., and LEAVENWORTH, C. S. Chemical studies on growth. III. The occurrence of glycogen in the embryo pig. Amer. Jour. Physiol. 20, 117. 1907-08. 11. MITCHELL, H. H. The minimum protein requirements of cattle. Bui. 67, Natl. Research Council. 1929. 12. MURRAY, H. A., JR. Physiological ontogeny. A. Chicken embryos. III. Weight and growth rate as functions of age. Jour. Gen. Physiol. 9, 39. 1925. 13. WARWICK, B. L. Prenatal growth of swine. Jour. Morph. and Physiol. 46, 59. 1928. UNIVERSITY OF ILLINOIS-URBANA