Genetic variation in reproductive responses to a high-energy diet in mice

Effects of a high-energy diet on reproduction were studied in 300 mice from lines selected for litter size and(or) 6-wk BW (L+, increased litter size; W+, increased body weight; L+W-, increased litter size and decreased body weight; L-W+, decreased litter size and increased body weight; and K, randomly selected control). Mice received a high-energy diet (HED; 3.8 kcal/g of ME) or a standard diet (STD; 3.3 kcal/g of ME) from 8 to 11 wk of age and were then mated and evaluated for ovulation rate and embryo survival through 17 d of gestation. The HED increased ovulation rate in all lines (P less than .05). The line x diet interaction was significant, with increased ovulation rate due to HED ranging from 9.9% in W+ to 24.2% in L-W+. Within-line regression coefficients of ovulation rate on ME intake (kilocalories from 10 to 11 wk) varied from .08 +/- .04 (P less than .05) in L+W- to .177 +/- .05 (P less than .01) in L+. In contrast, nonsignificant increases were observed in litter size (live fetuses at 17 d of gestation) due to HED. Effects of HED on embryo survival rate were significantly negative in L+ and L+W-; the decrease in L+ was a result of preimplantation losses, and the decrease in L+W- was due to postimplantation losses. The line x diet interaction was significant for postimplantation embryo survival. The results indicate significant genetic variation in reproductive responses to a high-energy diet in mice.     

Reproductive performance in a diallel cross among lines of mice selected for litter size and body weight

Genetic factors affecting female reproductive performance in lines of mice with a known history of selection were estimated from a 5 X 5 diallel cross. Lines were selected as follows: large litter size at birth (L+); large 6-wk body weight (W+); an index for large litter size and small 6-wk body weight (L+W-); the complementary index (L-W+) and randomly (K). Partitioning of direct and correlated responses for litter size, 6-wk body weight and related traits into average direct genetic (li) and average maternal genetic (mi) effects indicated that the magnitude of differences in li exceeded those in mi. Lines having positive responses in li were W+ greater than L+ greater than L-W+ for dam body weight, L+ greater than L+W- greater than W+ for litter size and L+ greater than (W+, L+W-) for litter birth weight, whereas L-W+ responded negatively for litter size. A positive association was found between mi for litter size and dam body weight, W+ and L-W+ being high and L+ and L+W- low for both traits. Female infertility and time from male exposure to parturition had relatively small correlated responses. Line rankings in general combining ability (gi) and net line effects were similar for the respective traits. Depending upon the line and trait involved, the relative contribution of average direct genetic and line direct heterotic (hi) effects to general combining ability [gi = (1/2) li + hi] varied. Line heterosis refers to average heterosis in crosses involving that line. Direct heterosis ( hij ) for each trait differed considerably among crosses. The three crosses showing the highest hij for litter size at birth, W+ X L-W+ (1.78), L+ X W+ (1.28) and L-W+ X L+W- (1.22), possibly had loci contributing directional dominance to litter size with frequencies of parental lines deviating in opposite directions relative to mean gene frequency. The correlation between absolute difference in parental line means and hij for litter size was not significant, suggesting that the magnitudes of absolute differences in parental means were not reliable predictors of divergence in gene frequency. Crossbred performance increased linearly with midparent values for litter size at birth (b = .88 +/- .09, R2 = .92) and dam parturition body weight (b = 1.13 +/- .04, R2 = .99), the latter trait showing an increase (P less than .01) in heterosis as midparent values increased.     

Postpartum performance in a diallel cross among lines of mice selected for litter size and body weight

Postpartum dam performance was studied in a complete diallel design involving five lines of mice. The selection criterion in each line was: large litter size at birth (L+); large 6-wk body weight (W+); an index for large litter size and small 6-wk body weight (L+W-); the complementary index (L-W+) and random (K). Females from the five lines and 20 reciprocal F1 crosses were mated to sires of a randomly selected control line (CC). Correlated responses in average direct genetic and average maternal genetic effects for dam body weight and litter size at parturition persisted throughout lactation, indicating important pleiotropic effects. Major correlated responses occurred for litter weight, feed intake and litter feed efficiency, primarily due to average direct genetic effects. Using general combining ability and net line effects as criteria for choosing among lines, L+ had a distinct advantage if the objective was to increase litter size in a crossing program. If the objective was to maximize litter weaning weight, then W+ would be favored for net line effects, while L+ and W+ would be about equivalent for general combining ability. None of the lines had an advantage for litter feed efficiency. Direct heterosis for dam weight at 12 and 21 d of lactation averaged 2.7 and 1.9%, while for litter size the respective averages were 7.4 and 7.3%. The W+ X L+W- cross exhibited overdominance for litter size. Direct heterosis was moderate for feed intake and litter weight, but was negligible for litter feed efficiency because of the mathematical relationship among the three traits. Maternal heterosis for preweaning progeny growth was suppressed because of heterosis for litter size in the dam. Grand-maternal effects on growth of the young were small and would not be an important consideration in choosing among these lines in a crossbreeding program.     

Ovulation rate and embryo survival during gestation and the effects of ovariectomy on maternal nurturing ability

Correlated responses to selection for increased litter size were studied in mice. The selected line (L+) was compared with an unselected control line (K') in two experiments. The first experiment provided a profile of correlated changes in female reproductive traits at d 0, 6, 14 and 18 of gestation. Experiment two examined the effects of ovariectomy on d 18 of gestation, sham surgery and no surgery on litter size and maternal performance. Females of the L+ line had increased (P less than .001) body weight, ovulation rate and uterine length at d 0 of gestation compared with K' females, but uterine weight and ovarian weight did not differ. Positive correlated responses (P less than .001) in uterine weight and length at d 6 and 14 of gestation were associated with a larger number of viable fetuses. Space per fetus was reduced (P less than .001) in the uterus of L+ females, but a lower fetal mortality was still maintained in L+ throughout gestation. Prenatal survival was about 10% higher (P less than .06) in L+, the major difference (P less than .01) occurring before implantation. A second experiment was conducted to determine the effect of ovariectomy on d 18 on litter size and maternal performance. In experiment two, no significant line X treatment interactions were found for maternal performance, indicating that both lines responded similarly to ovariectomy. Line L+ showed a positive correlated response in maternal performance. Ovariectomized females had a reduced (P less than .05) number born alive compared with sham-operated females, but the nonsurgically treated females were intermediate.(ABSTRACT TRUNCATED AT 250 WORDS)     

Genetic analysis of growth curve parameters for male and female chickens resulting from selection on shape of growth curve

The objectives of this research were to evaluate gender differences and selection on body weight as they affect growth curves of chickens. Marginal posterior densities of growth curve parameters were studied by Gibbs sampling on 10,671 male and female chickens originating from five lines. Line X-+ was selected on low body weight at 8 wk (BW8) and high body weight at 36 wk (BW36), line X+- on high BW8 and low BW36, X++ on high BW8 and BW36, X-- on low BW8, and BW36, and X00 was an unselected control line. Growth was modeled by a Gompertz function. Heritabilities and genetic correlations among parameters of the Gompertz curve were estimated. Marginal posterior densities were drawn for parameters of the growth curve and for sexual dimorphism at ages ranging from hatching to 1 yr. Lines selected for a higher BW8 had higher initial specific growth rates (L), higher maturation rates (K), and lower ages at inflection (T(I)). Lines selected for a higher BW36 had higher asymptotic body weights (A). Estimates of A, L, and T(I) were higher in males and K was higher in females. Difference between sexes for A was greater in the line selected for a lower BW8 and a higher BW36. Dimorphism for L and K was the lowest in lines X++ and X--, respectively. The greatest difference in T(I) was observed in the line selected for lower BW8 and BW36. Sexual dimorphism of body weight was lower at most ages in the lightest line. Before 15 wk, sexual dimorphism in X++ line was lower than in the line selected for higher BW8 and lower BW36. The increase in sexual dimorphism with body weight could be reduced by selecting animals on body weight at two ages instead of one, as is usually done in commercial lines.     

Protein (lysine) restriction in primiparous lactating sows: effects on metabolic state,somatotropic axis,and reproductive performance after weaning

Low protein intake during lactation has been demonstrated to increase the loss of body protein and to reduce the reproductive performance of female pigs. The objectives of the current experiment were 1) to determine whether protein (lysine) restriction alters levels of somatotropic hormones, insulin, follicle-stimulating hormone, and leptin around weaning, and 2) to evaluate the relationships between these eventual alterations and postweaning reproductive performance. One day after farrowing, crossbred primiparous sows were randomly allocated to one of two diets containing 20% crude protein and 1.08% lysine (C, n = 12) or 10% crude protein and 0.50% lysine (L, n = 14) during a 28-d lactation. Diets provided similar amounts of metabolizable energy (3.1 Mcal/kg). Feed allowance was restricted to 4.2 kg/d throughout lactation, and litter size was standardized to 10 per sow within 5 d after farrowing. Catheters were fitted in the jugular vein of 21 sows around d 22 of lactation. Serial blood samples were collected 1 d before (day W - 1) and 1 d after (day W + 1) weaning, and single blood samples were collected daily from weaning until d 6 postweaning (day W + 6). Sows were monitored for estrus and inseminated. They were slaughtered at d 30 of gestation. During lactation, litter weight gain was similar among treatment groups. Reduced protein intake increased (P < 0.001) sow weight loss (-30 vs -19 kg) and estimated protein mobilization throughout lactation (-4.1 vs -2.0 kg). On day W - 1, L sows had higher (P < 0.02) plasma glutamine and alanine concentrations, but lower (P < 0.05) plasma tryptophan and urea than C sows. Mean and basal plasma GH were higher (P < 0.001), whereas plasma IGF-I and mean insulin were lower in L than in C sows on day W - 1. Preprandial leptin did not differ between treatments on day W - 1, but was higher (P < 0.01) in L sows than in C sows on day W + 1. Mean FSH concentrations were similar in both treatments on day W - 1 (1.3 ng/mL), but L sows had greater (P < 0.001) mean FSH on day W + 1 than C sows (1.6 vs 1.2 ng/mL). The weaning-to-estrus interval (5 +/- 1 d) was similar in both groups. Ovulation rate was lower in L than in C sows (20.0 +/- 1 vs 23.4 +/- 1, P < 0.05). No obvious relationships between reproductive traits and metabolic hormone data were observed. In conclusion, these results provide evidence that protein (lysine) restriction throughout lactation alters circulating concentrations of somatotropic hormones and insulin at the end of lactation and has a negative impact on postweaning ovulation rate.     

Inheritance of litter size and its components in crosses between the D'man and Sardi breeds of sheep

Data on ovulation rate, litter size and embryo survival of 364 Sardi (S), D'man (D), S x DS, DS x S, S x D, D X S (F1), F2, D x DS and DS x D ewes mated for first and second lambing to F1 rams were analyzed. Breed group, birth group and season had significant effects on ovulation rate and litter size but not on embryo survival. D'man ewes had the highest ovulation rate (2.79) and litter size (2.00), with an essentially linear increase in each of these variables with percentage of D'man inheritance in the ewe (b = .017 +/- .001 CL and .009 +/- .001 lambs born). Embryo survival was influenced only by the number of ova shed. D'man direct genetic effects were higher (P less than .01) than those of Sardi for ovulation rate (+1.78) and litter size (+1.08) but did not differ for embryo survival (-.07). Maternal effects differed little for any of the three traits. Individual heterosis estimates were negative and significant for ovulation rate but not significant for litter size and embryo survival. Maternal heterosis and epistatic recombination effects were small and not significant for any trait.     

Flushing and altrenogest affect litter traits in gilts

Gilts (n = 267) were allotted to flushing (1.55 kg/d additional grain sorghum), altrenogest (15 mg.gilt-1.d-1) and control treatments in a 2 x 2 factorial arrangement. Altrenogest was fed for 14 d. Flushing began on d 9 of the altrenogest treatment and continued until first observed estrus; 209 gilts (78%) were detected in estrus. The interval from the last day of altrenogest feeding to estrus was shorter (P less than .05) with the altrenogest + flushing treatment (6.6 +/- .2 d) than with flushing alone (7.6 + .3 d). Ovulation rates (no. of corpora lutea) were higher (P less than .05) in all flushed gilts (14.5 +/- .4 vs 13.4 +/- .4), whether or not they received altrenogest. Flushing also increased the total number of pigs farrowed (.9 pigs/litter; P = .06) and total litter weight (1.43 kg/litter; P = .01), independent of altrenogest treatment. Number of pigs born alive and weight of live pigs were higher for gilts treated with altrenogest + flushing and inseminated at their pubertal estrus than for gilts in all other treatment combinations. In contrast, gilts receiving only altrenogest had greater live litter weight and more live pigs born when inseminated at a postpubertal estrus than when inseminated at pubertal estrus. We conclude that flushing increased litter size and litter weight, particularly for gilts that were inseminated at their pubertal estrus. Increased litter size resulted from increased ovulation rates, which, in nonflushed gilts, limited litter size at first farrowing.     

Effects of differential ewe condition at mating and early postmating nutrition on embryo survival.

Ewes in two trials were given either a high (H) or a low (L) level of premating nutrition for 19 wk followed by 6 wk of either H or L postmating nutrition to examine effects on reproductive performance. Trial 1 ewes were 5- to 8-yr-old Polypays and Trial 2 ewes were 3-yr-old Polypay and Coopworth x Polypay crosses. Ewes given L nutrition premating were either immunized with androstenedione-7-carboxyethylthioether:human serum albumin (also known as ovandrotone or Fecundin) in (diethylamino)ethyl-dextran adjuvant (Trial 1) or flushed for 3 wk premating (Trials 1 and 2) to enhance ovulation rates. All ewes were synchronized for mating in both trials. Trial 1 premating treatments created a difference of 10 kg in BW and 1.1 in condition score units between H and L ewes preflushing; flushing halved the BW difference. Ovulation rates averaged 2.58 and were similar for H, L-flushed, and L-immunized (LI) ewes; however, both conception rate and litter size were lowest for immunized ewes. Among both twin and triple-ovulating ewes, highest mean litter size was produced by H ewes, followed in order by L and LI ewes. High postmating nutrition increased BW by 6 kg vs slight weight loss in L ewes, but postmating treatments did not affect litter size of either twin or triple ovulators. The H and L premating groups of Trial 2 differed by 18 kg and 2.2 condition score units preflushing. The H ewes exhibited higher ovulation rates (overall mean = 2.63) but lower conception than the L ewes to synchronized estrus. Litter size averaged 2.15 for H ewes vs 1.82 for L ewes. Among both twin and triple ovulators, L ewes produced fewer lambs than H ewes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Direct and correlated responses to two-stage selection for ovulation rate and number of fully formed pigs at birth in swine

Our objectives were to estimate responses and genetic parameters for ovulation rate, number of fully formed pigs at birth, and other production traits following two-stage selection for increased ovulation rate and number of fully formed pigs. Eight generations of selection were practiced in each of two lines. One selection line was derived from a line that previously selected eight generations for an index to increase ovulation rate and embryonic survival (the IOL pigs). The other selection line was derived from the unselected control line of the index selection experiment (the COL pigs). The control line (C) was continued with random selection. Due to previous selection, Line IOL had greater ovulation rate (4.24 +/- 0.38 and 4.14 +/- 0.29 ova) and litter size (1.97 +/- 0.39 and 1.06 +/- 0.38 pigs) at Generation 0 of two-stage selection than did Lines COL and C. In Stage 1, all gilts from 50% of the largest litters were retained. Approximately 50% of them were selected for ovulation rate in Stage 2. Gilts selected for ovulation rate were mated to boars selected from the upper one-third of the litters for litter size. At Generations 7 and 8, differences in mean EBV for ovulation rate and litter size between Lines IOL and C were 6.20 +/- 0.29 ova and 4.66 +/- 0.38 pigs; differences between Lines COL and C were 2.26 +/- 0.29 ova and 2.79 +/- 0.39 pigs; and differences between Lines IOL and COL were 3.94 +/- 0.26 ova and 1.86 +/- 0.39 pigs. Regressions of line mean EBV on generation number were 0.27 +/- 0.07 ova and 0.35 +/- 0.06 pigs in Line IOL; 0.30 +/- 0.06 ova and 0.29 +/- 0.05 pigs in Line COL; and 0.01 +/- 0.07 ova and 0.02 +/- 0.05 pigs in Line C. Correlated responses were decreased age at puberty and increased number of pigs born alive, number of mummified pigs, prenatal loss, and individual and litter birth weight. Two-stage selection for ovulation rate and number of pigs per litter is a promising procedure to improve litter size in swine.     

Effects of pregnant mare's serum gonadotropin on reproduction in four genotypes of gilts(1)

SUMMARY: Effects of PMSG and genotype on various measures of reproductive efficiency were investigated. Prenatal data were obtained at 40 d of gestation from 96 gilts representing four genotypes. Data on Duroc (D), Yorkshire (Y), Synthetic (Large White × Landrace) (SYN), and Crossbred Duroc × Yorkshire (XB) gilts were collected from January, 1990 through May, 1991. Litter size (LS) data were collected from 482 farrowings of siblings. Treatment with exogenous hormones significantly increased number of corpora lutea (CL), number of embryos (EN), ovum wastage, (OVWS) and embryo length (ELG). Breed group differences (P < .05) were detected for natural ovulation rate, hormone-induced ovulation rate, CL, OVWS, ELG, embryo weight, ovum success, uterine length, ovary weight, range and variance of within-litter embryo weight (RWT and VWT), and litter size born alive. Natural ovulation rates for D, Y, SYN and XB were 10.46 ± 1.61, 12.64 ± 1.41, 14.10 ± .99 and 10.90 ± 1.47, and hormone-induced ovulation rates were 15.00 ± 1.53, 17.69 ± 1.40, 19.43 ± 1.17 and 12.19 ± 1.43, respectively. Range and variance of within-litter embryo length were not affected by either treatment or genotype. Increases in RWT and VWT observed in D and XB gilts after PMSG treatment did not adversely affect embryo survival to 40 d gestation. Significant genetic differences existed for litter size at birth. The PMSG treatment and interactions with PMSG were not significant for litter size born alive. Breed groups seem to differ for CL and EN in response to PMSG but only Yorkshire showed any response in LS (P < .10). Although PMSG increased ovulation rate in siblings by 4.06 ova and number of embryos at 40 d gestation by 1.87 compared with control gilts, there were no differences in litter size born alive due to PMSG treatment. The increase in ovulation rate and number of embryos generated by PMSG seems to be negated by fetal losses occurring both before and after 40 d of gestation. ZUSAMMENFASSUNG: Einflüsse von Stutenserum-Gonadotropin (PMSG) auf Reproduktionsmerkmale von vier Genotypen bei Jungsauen Einflüsse von PMSG und Genotyp auf verschiedene Merkmale der Reproduktion wurden untersucht. Daten wurden am 40. Tr?chtigkeitstag von 96 Jungsauen von vier Genotypen-Duroc (D), Yorkshire (Y), Synthetik (Edelschwein × Landrasse (SYN)) und Kreuzungen-Duroc × Yorkshire (XB) zwischen Januar 1990 und Mai 1991 erhoben. Wurfgr??e (LS) wurden von 492 Würfen von Geschwistertieren erhoben. Behandlung mit exogenem Hormon steigert signifikant die Zahl der Gelbk?rper (CL), Zahl der Embryonen (EN), Ovarverlust (OVWS) und Embryol?nge (ELG). Differenzen zwischen Genotypen wurden für natürliche und hormoninduzierte Ovulationsrate, CL, OVWS, ELG, Embryogewicht, Embryoerfolg, Geb?rmutterl?nge, Ovargewicht, Streuungsbereich und Varianz des Embryogewichtes von Wurfgeschwistern (RWT und VWT) und Zahl lebendgeborener Ferkel erhoben. Die natürlichen Ovulationsraten für D, Y, SYN und XB waren 10,46 ± 1,61, 12,64 ± 1,41, 14,10 ± 0,99 und 10,90 ± 1,47, und die hormoninduzierten 15,00 ± 1,53, 17,69 ± 1,40, 19,43 ± 1,17 und 12,19 ± 1,43. Streuungsbereich und Varianz zwischen Embryonenl?nge eines Wurfes wurden weder durch Behandlung noch Genotyp tangiert. Steigerungen in RWT und VWT in D und XB Jungsauen nach Hormonbehandlung hat Embryoüberleben bis 40 Tage nicht beeintr?chtigt. Signifikante genetische Unterschiede existieren zwischen Wurfgr??e bei Geburt. Hormonbehandlungen und Interaktionen mit Genotypen waren für die Wurfgr??e nicht signifikant. Rassengruppen scheinen für CL und EN im Hinblick auf Hormonbehandlung sich zu unterscheiden, aber nur Yorkshire zeigten Reaktion bei LS (P < .1). Obwohl das Hormon die Ovulationsrate um 4,06 Eier und Zahl der Embryonen bei 40 Tagen um 1,87 gegenüber Kontrollsauen vergr??erte, verblieben keine Unterschiede in Wurf gr??e. Die Steigerung der Ovulationsrate und Zahl der Embryonen nach Hormonbehandlung scheint durch F?talverluste vor und nach 40 Tagen Tr?chtigkeit eliminiert zu werden.     

Prediction and causation of litter market traits from preweaning and weaning characteristics in commercial meat rabbits

Market data on 1,315 rabbits from 201 litters from Californian (CAL), New Zealand White (NZW), CAL X NZW and NZW X CAL dams bred to CAL, NZW and Flemish Giant sires were subjected to multiple regression and path analyses. Market traits observed in litters at 56 d included average kit weight (A56W), litter size (LS56), total litter weight (L56W) and within-litter uniformity in individual weights (LCV). Preweaning variables as covariates included in the model were dam metabolic body weight (DMW), litter born (LSB), litter birth weight (LBW), milk yield from 1 to 21 d (MY) and feed intake from 1 to 28 d of the dam and litter (FI). Results from multiple regression analyses indicated linear and quadratic effects (P less than .20) due to LSB and MY for all four market characters. The LBW influenced (P less than .05) LS56 and L56W, and FI affected (P less than .05) LS56, L56W and LCV. Separate analyses were conducted involving 28-d weaning and feed intake variables as covariates: litter size weaned (LSW), litter weaning weight (LWW) and litter feed intake from 28 to 56 d (LFI). The three weaning covariates were important (P less than .05) for all market traits except LS56 (LWW was not significant). The most accurate regression equations were obtained from the weaning model for prediction of L56W and LS56 (R2 = .68 and .78). Path analyses revealed that preweaning covariates generally had direct rather than indirect effects on market traits. Both direct and indirect effects of weaning covariates were important for market traits. Results suggest that litter market traits of size and weight can be predicted with a reasonable degree of accuracy.     

Effect of energy and lysine intake in gestation on sow performance

Nutrient intake during gestation has an impact on gestation parameters and subsequent lactation performance. The objectives of this experiment were to determine the impact of feeding two levels of amino acids in gestation on sow BW changes in gestation and lactation, and litter size, and to evaluate a factorial method for determining daily energy requirements. At mating, 419 sows (Camborough 15; Pig Improvement Canada, Acme, AB) were assigned randomly within Parities 1, 2 or 3+ to a gestation diet containing either 0.44% (low lysine) or 0.55% (high lysine) total lysine and 3,100 kcal DE/kg; other indispensable amino acids were adjusted to lysine based on ideal protein ratios. Feed allowance in gestation was determined factorially using estimated DE requirements for maintenance, maternal gain, and conceptus growth. Sows were allowed free access to the lactation diet. Gestation BW gain from d 0 to 110 was affected by parity (61.2, 60.0, and 42.3 kg for Parity 1, 2, and 3+, respectively; P < 0.05) but not (P > 0.10) by gestation lysine level. Sow BW changes from d 0 of lactation to weaning were affected by parity (0.5, 6.8, and 5.8 kg for Parity 1, 2, and 3+, respectively; P < 0.01) and gestation BW gain (P < 0.01), but not by gestation lysine level (5.0 vs 3.8 kg for low and high lysine, respectively; P > 0.10). Total piglets born was affected by parity (11.5, 12.1, and 12.5, for Parity 1, 2, and 3+, respectively; P < 0.01) and increased with increasing sow BW gain (P < 0.05). Total piglets born alive (mean = 11.2) was increased with increasing sow BW gain (P < 0.05). Total litter weight born alive was affected by parity (15.9, 18.6, and 19.4 kg for Parities 1, 2, and 3+, respectively; P < 0.01) and gestation BW gain (P < 0.05). The model used to determine daily energy intake requirements resulted in an average BW gain of 10.6 kg above the targets set by the model. Total lysine intakes greater than 10.6 g/d in gestation did not improve sow productivity. Setting target weight gains in gestation and feeding to meet these targets may not always provide predictable results due to a number of factors that affect the energy requirement in the sow.     

Growth, development, and carcass composition in five genotypes of swine.

An experiment with 127 barrows representing five genotypes, 1) H x HD, 2) SYN, 3) HD x L[YD], 4) L x YD, and 5) Y x L (H = Hampshire, D = Duroc, SYN = synthetic terminal sire line, L = Landrace, and Y = Yorkshire), was conducted to evaluate growth and development of swine from 59 to 127 kg live weight. Animals were allowed ad libitum access to a pelleted finishing diet containing 18.5% CP, .95% lysine, and 10.5% fat, with an energy density of 3,594 kcal of ME/kg. Pigs were serially slaughtered at either 59, 100, 114, or 127 kg live BW. After slaughter, carcasses were chilled and backfat was measured at four locations. The right side of each carcass was fabricated into primal cuts of ham, loin, Boston Butt, picnic, and belly. Composition of each primal cut was determined by physical dissection into lean, fat, bone, and skin. Estimated allometric growth coefficients for carcass length, carcass weight, and longissimus muscle area relative to BW; carcass lean, fat, bone, and skin relative to both BW and carcass weight; and lean in each of the primal cuts relative to total carcass lean did not differ (P greater than .05) among genotypes. Relative to BW, the pooled growth coefficient(s) for carcass weight was (were) greater (P less than .001) than unity, whereas those for carcass length, longissimus muscle area, and backfat at first rib were smaller (P less than .001) than unity. Those for other backfat measurements were close to 1.00. Relative to either BW or carcass weight, the pooled coefficient(s) for fat was (were) greater (P less than .001) than unity, whereas those for lean, bone, and skin were smaller (P less than .001) than unity. Growth of lean, backfat, bone, and skin in the carcass were nearly linearly associated with increases in BW. The increase in fat weight was curvilinear as the pig grew and was accelerated in later growth stages, indicating that carcass fat percentage increased with increased BW.     

Effect of boar presence before and after weaning on estrus and ovulation in sows

Two hundred sixty-two sows were used to investigate the effects of boar exposure during the last week of nursing (BPRE) and after weaning (BPOST) on the return to estrus. Because approximately one-half of the sows were weaning their first litter, a third factor, primiparous vs multiparous (LITT), was considered in the statistical analysis. To evaluate the effect of treatment on ovarian activity, the sows were also blood-sampled twice weekly for 3 wk after weaning for the measurement of plasma progesterone concentrations as an index of ovulation. Boar exposure after weaning was the most important stimulus of early ovulation and estrus after weaning (P less than .001). A greater proportion of first-litter sows exhibited estrus later (P less than .02) and ovulated later (P less than .09) than did multiparous sows. First-litter sows were unaffected (P greater than .10) by boar exposure before weaning. Multiparous sows were sensitive to boar exposure during nursing. Maximal boar exposure for these sows (BPRE + BPOST) resulted in 95% of sows in estrus and ovulating within 20 d of weaning. No boar exposure resulted in 45% and 38% anestrus and anovulatory sows. Boar exposure, either before or after weaning, was effective in reducing the number of anestrus and anovulatory sows to between 15 to 30%. The effects of BPRE and BPOST on return to ovulation were additive and approximately equal.     

The effect of zeranol on live weight gain, feed intake and carcass composition of steers during compensatory growth

To evaluate the effect of zeranol implants in steers on compensatory ++growth, 80 steer calves (9 mo of age; 200 kg) were fed at two feeding levels (RO = 9.2 MJ ME/kg DM; R1 = 6.9 MJ ME/kg DM) for 119 d (Period 1). During Period 2, steers were full-fed to 400 kg BW with (Z1) or without (ZO) zeranol implants. Ten steers were slaughtered at the end of Period 1 to estimate carcass composition. Differences of 100 kg in BW were achieved by restriction in Period 1. Subsequent to restriction, cumulative ADG remained greater (P less than .05) up to the 24th wk of recuperation and implants increased (P less than .001) BW gain by 31% and 24% for RO and R1, respectively. The average daily energy intake (ME/W(.75) in Period 2 was similar for all treatments. Feed conversion was improved by 21.5% (P less than .05) by implants. At the end of Period 2 the R1ZO had 8.6 kg less muscle (P less than .001), 2.9 kg less bone (P less than .001) and 5.9 kg more fat (P less than .05) than the ROZO. In comparison, the carcasses of the implanted animals did not show significant differences (P greater than .05) due to restriction. Carcass daily gains were increased by previous restriction (P less than .01) and implants (P less than .05). Zeranol increased daily live weight gain and feed conversion in animals in continuous growth as well as in those observed in compensatory growth an tended to eliminate a tendency for higher content of fat in carcasses of nonimplanted animals making compensatory growth.     

Intake of direct cut or wilted grass silage as related to chewing behavior, ruminal characteristics and site and extent of digestion by heifers

Six nonpregnant Friesian heifers (516 kg avg BW) with ruminal and duodenal cannulas were used to examine intake of direct cut (DC) or wilted (W) grass silage in relation to chewing behavior, ruminal characteristics and site and extent of digestion. Dry matter content of the silages was 20.3% and 40.3%, and feed intake averaged 1.88% and 2.17% of BW (P less than .01), respectively. Mean ruminal osmolality was 291 mosm/liter for the DC and 318 mosm/liter for the W silage (P less than .05), with extreme values exceeding 350 mosm/liter for the W silage at 1 h to 2 h postfeeding. There was a shift from eating to ruminating on W silage associated with a longer duration of the average rumination bolus cycle (P less than .01). Duration of chewing time per kilogram of DM intake was 103.5 min and 91.7 min (P less than .05) for the DC and W silages, respectively. Fecal mean particle length was 2.2 times greater (P less than .01), accompanied by higher spread coefficients (P less than .001), for the W silage. No differences occurred between silages in ruminal digestibility of OM and NDF. In the total digestive tract, apparent digestibilities of OM and NDF were depressed after wilting grass prior to ensiling (P less than .01), but the proportion of digestible OM apparently digested in the rumen was .74 for both silages.(ABSTRACT TRUNCATED AT 250 WORDS)     

Age, dose of FSH and other factors affecting superovulation in Holstein cows

Effects of age of donor and other factors on superovulation and production of transferable embryos were investigated. Data were obtained on 987 recoveries of embryos performed between November 1980 and June 1984 by Select Embryos, Inc. The 339 Holstein donors ranged in age from 1.8 to 17.8 yr. The effects of age of donor and dose of follicle stimulating hormone (FSH) were examined using regression analysis. For on-farm recoveries, numbers of embryos, rates of fertilization, quality scores of all embryos and numbers of transferable embryos decreased (P less than .01, P less than .001, P less than .05, P less than .01, respectively) with increasing age of donor. For in-clinic recoveries, numbers of embryos plus ova recovered were affected by age of donor, dose of FSH and the interaction of the two (P less than .05). Among older donors, increasing doses of FSH were associated with an increase in the number of ova plus embryos recovered. However, among younger donors, increasing doses of FSH had a negative effect. Numbers of embryos, rates of fertilization and numbers of transferable embryos decreased (P less than .05) with advancing age and increased (P less than .05) with increasing doses of FSH. Greater numbers of ova plus embryos were recovered when treatment with FSH was begun on d 10 or 11 as compared with d 7, 8, 9, 12, 13 or 14 (P less than .001). It was concluded that an increase in age of donor had a negative influence on the success of superovulation and the production of transferable embryos, and that the response to FSH was affected by age of donor.     

Direct responses to selection for increased litter size, decreased age at puberty, or random selection following selection for ovulation rate in swine

Nine generations of selection for high ovulation rate were followed by two generations of random selection and then eight generations of selection for increased litter size at birth, decreased age at puberty, or continued random selection in the high ovulation rate line. A control line was maintained with random selection. Line means were regressed on generation number and on cumulative selection differentials to estimate responses to selection and realized heritabilities. Genetic parameters also were estimated by mixed-model procedures, and genetic trends were estimated with an animal model. Response to selection for ovulation rate was about 3.7 eggs. Response in litter size to selection for ovulation rate was .089 +/- .058 pigs per generation. Average differences between the high ovulation rate and control lines over generations 10 to 20 were 2.86 corpora lutea and .74 pigs (P less than .05). The regression estimate of total response to selection for litter size was 1.06 pigs per litter (P less than .01), and the realized heritability was .15 +/- .05. When the animal model was used, the estimate of response was .48 pigs per litter. Total response in litter size to selection for ovulation rate and then litter size was estimated to be 1.8 and 1.4 pigs by the two methods. Total response to selection for decreased age at puberty was estimated to be -15.7 d (P less than .01) when data were analyzed by regression (realized heritability of .25 +/- .05) and -17.1 d using the animal model. No changes in litter size occurred in the line selected for decreased age at puberty. Analyses by regression methods and mixed-model procedures gave similar estimates of responses and very similar estimates of heritabilities.     

Influence of prenatal and postnatal fraternity size on reproduction in swine

Hypotheses of a negative association between fraternity size (size of litter in which an individual develops prior to birth or is reared following birth) and ovulation rate or litter size were tested by examining reproduction of females born or reared in varying prenatal and postnatal fraternities. Gifts were randomly assigned to develop prenatally and be reared postnatal in small or large fraternities. Dams of experimental animals were randomly assigned to one of two prenatal fraternity size treatments, either unilateral oviductal ligation (to bear a small prenatal litter) or no ligation (to bear a normal prenatal litter). Whereas this did result in differences (P less than .01) in litter size at birth (small = 6.2 +/- .4 vs large = 9.6 +/- .9), there was considerable overlap in observed litter sizes between ligated and nonligated dams. Consequently, effects of prenatal fraternity size were examined by regression. Distinct differences in postnatal fraternity size were created by randomly assigning piglets to small (5 piglets) or large (10 piglets) postnatal fraternities within 24 h of birth. Differences in postnatal fraternity size were maintained through weaning at 3 wk (small = 4.9 +/- .1 vs large = 9.4 +/- .2). Weights at birth (regression of birth weight on prenatal fraternity size = -.07 +/- .02, P less than .01) and weaning (small = 6.09 +/- .15 vs large = 5.46 +/- .17 kg, P less than .01) were heavier for gilts from small prenatal and postnatal fraternities, respectively, compared with gilts from large fraternities. Effects of prenatal and postnatal size on BW did not persist following weaning (P greater than .20).