Search

Effects from 34 generations of selection, either up (U) or down (D), for 3- to 9-wk weight gain on genetic direct and postnatal maternal effects, dam size and maternal efficiency were evaluated in 25 cross-fostered sets of rats. Direct genetic effects on 12-d pup weight were 14 and 9% above controls (C) for U and D lines, respectively (P<.01). Postnatal maternal effects on 12-d pup weight were also 11% higher for the U line (P<.01), but not different from C for the D line. Females of the U line were heavier (P<.01) by 13% at mating, 12% at parturition and 15% at 12 d of lactation, relative to controls. They also produced 11% greater total litter weight at 12 d and consumed 9% more feed, but were only nonsignificantly lower in feed per unit of pup 12-d litter weight. Females of D line were −8, −7 and −3% relative to controls in the three weights, but did not differ from controls in 12-d litter weight, feed consumed or in feed efficiency during lactation.

Response to selection for up (U) and (D) 3- to 9-wk gain in rats on average daily gain (ADG), average daily feed intake (ADD, gain/feed (G/F), body composition (BC), fasting metabolic rate per unit metabolic size (MR) and partial efficiency of weight gain (ADG/Fg) was evaluated after 34 generations of mass selection. At 3-wk weaning, 120 litters representing F1crosses of two replicates within each of the U1D and control (C) selection lines were divided within sexes between bulk-feeder and tube-feeder cage types for recording feed intake until 9 wk of age. Rats from tube-feeder cages representing 16 litters/line were utilized for MR and BC data. Response in ADG was asymmetrical; 16% higher for U line but only 8% lower in D line, compared with C line. Correlated responses were positive and significant in both U and D lines for ADI (6% and −3%) and G/F (5% and −5%). Line differences in MR were not significant but both selected lines were slightly higher than C line in MR at 6 wk of age, and the reverse at 9 wk of age. Over the period of 6 to 9 wk of age, maintenance requirements per unit metabolic size and ADG/Fg were 1 and 5% above for the U and −1 and −4% for D lines, relative to C line. Females of both selected lines were fatter than C line (P<.05) at 9 wk of age, but only D line males were fatter than C line.

Reproductive performance was evaluated on lines of rats selected 34 generations for up (U) and down (D) 3- to 9-wk weight gain and from a control (C). Direct response to 3- to 9-wk weight gain was 16% in U and −8% in D lines. Inbreeding was similar among lines. Both selection lines were poorer in percentage of fertile pairs than the C line, especially so in D (P<.10). The lines differed (P<.05) in litter size born with means of 11.4, 10.4 and 9.6 for U, C and D, respectively. The significant positive correlated response in litter size corresponded to that expected from intraline association with female body weight. Selection for increased postweaning gain resulted in 5% earlier age but little change in weight at vaginal opening. The D line was similar to C in age, but 7% lighter in weight at vaginal opening. The U line was significantly higher (14, 12 and 69%) for ovulation rate, number of fetuses and post-implantation losses, but not for pre-implantation losses. The D females were similar to C females in all components of litter size. Males of all lines were similar in age at first mating, but U males were 22% heavier than C males in weight at first mating. A positive correlated response in weight of testes at 91 d of age disappeared when adjusted for intraline association with body weight.

Differences in growth, chemical body composition and visceral organ development were evaluated in three genetic stocks: Beltsville Highfat (HF) and Lowfat (LF) Duroc-Yorkshire composites and a Hampshire × Large White cross (CX). Ten sets of littermate barrows were used from each stock. One pig from each set was slaughtered at 10, 17 and 24 wk of age. After slaughter, each pig was dissected into three fractions: carcass, head and feet, viscera and blood. Backfat was measured at three locations and visceral organs were weighed separately. Each fraction was frozen, ground, sampled and analyzed in duplicate for protein, fat, water and ash. The CX pigs were heaviest at all ages and contained the most fat-free mass (FFM). The HF pigs were smallest and contained the most fat, while LF pigs tended to be intermediate. The LF pigs deposited a greater proportion of weight in head and feet and a greater proportion of total FFM in the carcass than HF and CX pigs. Estimated allometric growth coefficients for non-fat chemical components relative to empty body weight (EBWT) were lower for HF than LF and CX, which were similar. Coefficients for fat were similar among stocks yet intercepts differed widely. Relative to total FFM, water increased at a faster rate and ash a slower rate in CX pigs compared to HF and LF. Growth coefficients were calculated for internal organs relative to EBWT. Coefficients for organs of the digestive tract were not different among stocks. However, significant differences among stocks were found for heart, lung, spleen and liver that were not explained by differences in body composition.

Effects on components of net life-cycle input costs/gram of lean tissue output were modelled for responses from 14 generations of family selection for rate (LG) or for efficiency (LE) of postweaning lean gain. Compared with unselected controls (C), LG and LE rats were heavier by 15 and 3% at 3-wk weaning, 23 and 12% at 8 wk and 23 and 13% at 15-wk breeding age. The LG and LE rats ate 12 and 5% more feed than C rats, gained protein 27 and 17% faster and thus 13 and 11% more efficiently from 3 wk to a mean 250 g final weight. The LG rats were fatter and LE rats less fat than C rats (6.7 and 6.0 vs 6.4%). Fasting heat loss was 6% below C for both LG and LE rats. The LG rats were slightly below C rats in fertility, but were above C in litter size and preweaning viability; LE rats had slightly smaller litters and poorer survival than C rats. The production system assumed “marketing” of females after weaning first litters and of surplus young at 6, 7, 8 or 9 wk of age. Total feed input/protein output (g/g) for 6-, 7-, 8- and 9-wk marketing age relative to C was −5, −2, −3 and −3% in LG, but −3, −2, −4 and −6% in LE, mostly from reduced breeder feed in LG, but from feed for both breeders and young in LE. Compared with C, nonfeed costs for breeders and young were −19 and −16% in LG but were only −7 and −10% in LE. Total costs at 6- to 9-wk end points relative to C were −12 to −8% in LG and −4 to −8% in LE. Optimum end points were below 6 wk for LG, 7 to 8 wk for LE and 7 wk for C, and would be still younger for lower ratios of nonfeed to feed costs. At optimum age end points for each, total costs/g protein relative to C were −9% for LG, but only -5% for LE, because of the lower LE reproductive rate. These results question direct selection for the postweaning lean tissue feed conversion ratio.

The effects of postnatal litter size on pre-and postweaning growth, daughter's litter size and rebreeding performance of the dam were examined in rats that had undergone 14 generations of selection for rate (LG) or efficiency (LE) of postweaning protein gain followed by relaxed selection, and in a randomly selected control line (C). Data came from generations 23 to 24 (standardized litters) and 25 to 26 (unstandardized litters). Generation 25 dams were remated at weaning for two additional parities. Regressions of average pup weight on average postnatal litter size were negative and increased in magnitude from birth to weaning, but decreased with parity number. Average litter size from birth to weaning (3 wk) affected postweaning weights at 5 and 7 wk, but compensatory growth occurred, especially during wk 3 to 5. The effect of dam's litter size (the litter in which the daughter was born) on daughter's weight was still negative and significant at mating and affected litter size of daughters. This negative maternal effect on daughter's litter size was larger when the dam's litter was not standardized. Litter size weaned also affected rebreeding interval of females.

Direct and correlated responses were evaluated for nine generations of full-sib family selection for postweaning rate (LG) and efficiency (LE) of protein deposition in rats. Selection in LG was based on rate of protein gain (DP) calculated from mean live weight gain of standardized litters (4 ♂,5 ♀) and composition of three sibs under ad libitum (B) feeding. Selection in LE was based on rate of protein gain/feed (PE) to a fixed age or weight under more limited (T) access to feed. There were two replicates of 20 males and 40 females each in selected LG and LE lines and three replicates of 20 single-pair matings each in unselected controls (C). Standardized selection differentials for family means of parents were about .9 σ for generations 7 to 15 in both LG and LE. Inbreeding increased about 1%/generation until replicates were combined in generation 12, and reached 13% in selected and 9% in control lines at generation 20. In generations 5 and 15 to 20, each line was evaluated under both feeding environments. Responses per generation as percentages of controls in LG and LE lines were 2.2 and 1.6% for DP, 1.2 and .8% for PE, .5 and 1.2% for 3-wk weaning weight, 2.1 and 1.9% for daily 3- to 8-wk gain, 1.2 and .8% for daily feed, 1.1 and .7% for live weight gain/feed, 1.9 and 1.5% for female weight after parturition and 1.8 and 1.3% in female weight after weaning their first litter. Responses were nonsignificant in percentage skin, protein content of skinned empty body and litter size born. Realized heritability was .40 ± .07 for DP and .07 ± .04 for PE. During five subsequent generations of relaxed selection, linear decline in 3- to 8-wk growth rate/generation was greater in LE than in LG (−2.8 vs −1.9%) and under T than B feeding (−2.9 vs −1.8%). Decline in feed intake was −2% in both lines, but more in females than in males. Live weight gain/feed declined −1.8% in LE, but differed between males (−1.3%) and females (1.1%) in LG. Breeding female weights declined −1.7% in LE and −1.5% in LG. Litter size was unchanged. Selection for faster postweaning lean growth was as effective and responses were more stable under relaxed selection, than from direct selection for more efficient lean growth.

Ewe performance was compared for five pure breeds of sheep (Finnsheep, F; Rambouillet, R; Dorset, D; Targhee, T; Suffolk, S) and the crosses in development of two maternal composite lines (C1 = ½F¼R¼D and C2 = V½F¼T¼S). The data involved 10,959 breeding season records of 4,219 ewes by 412 sires. Ewe production and the components (fertility, litter size, neonatal and preweaning lamb survival and mean lamb weaning weight) were adjusted for age and standardized across season of lambing and years. The D and F ewes produced more weight of lamb/ewe exposed than R, S and T ewes because of higher D and F fertility, higher D lamb survival and larger F litters. First cross and inter se generations of C1 and C2 ewes averaged 17 to 27% higher fertility than the parental mean. Litter size averaged about one lamb higher for F than for other pure breeds, but only slightly higher for C1 and C2 than for the mean of F and other breeds. Lower neonatal survival for F than for other breeds and crosses was associated with the larger F litters and with 2 to 8% positive heterosis in the crosses. Preweaning survival of suckled and nursery lambs was low for F and S and positive heterosis ranged from 9 to 19% in crosses. Mean lamb weaning weights were highest for S, lowest for F, with little heterosis in crosses. Crossbred ewes reared .3 to .4 more lambs than mean for parental pure breeds. Heterosis in C1 and C2 ranged from 11 to 28% for lambs born, 27 to 43% for lambs weaned and 29 to 44% for weight of lamb weaned/ewe exposed. Decline in heterosis with inter se mating of crosses was no greater than expected from the reduction in predicted heterozygosity.

Season of lambing and other environmental effects on ewe performance were analyzed for purebred Finnsheep (F), Rambouillet (R), Dorset (D), Targhee (T) and Suffolk (S) and the generations of crosses in development of two maternal composite lines (½F¼R¼D) and (½F¼T¼S) in accelerated (January, May and September) or annual April lambing. The data involved 10,959 ewe breeding season records for 4,219 ewes of 412 sire families over 4 yr. Various measures of ewe productivity and its components (fertility, litter size, neonatal and preweaning survival and weaning weight) were analyzed. Fertility was higher for annual April than for accelerated May or January lambing and was sharply lower for September lambing. Fertility of F and F-cross ewes was significantly higher for May and lower for January lambings relative to R and D ewes. Litter size also was higher in annual April (1.9) than in January (1.8) or May (1.7) and September (1.4). Neonatal and preweaning survival was higher in September when litter size was smaller. Mean weaning weights were depressed in the larger April and May litters. Thus, weight of lambs weaned/ewe exposed was higher for annual April than for May and January lambing and was very low for September lambing. Hormone treatment of ewes for September lambing increased fertility from 16 to 44% and litter size from 1.6 to 1.8. Short lambing interval (8 mo vs 12+ mo) reduced mean ewe fertility by five percentage points, and most for the January lambing of Finnsheep ewes.

A bio-economic model of swine production was used to simulate expected performance effects of breeds in alternative breeding systems on total costs/100 kg of live weight (EWW) or/100 kg lean (ELW) for marketing at 100 kg live weight and on costs/100 kg lean for marketing at mean 185-d weight (ELA). Effects of heterosis and of six U.S. breeds were simulated for integrated industry purebred (P), two-breed specific (2S), backcross (2B) and rotation cross (2R), and three-breed specific (3S) and rotation cross (3R) breeding systems. Traits considered were age at puberty (-PUB), conception rate (CR), litter size born alive (NBA), preweaning viability (VIAB), milk production (MILK), age at 100 kg live weight (-DAYS) and empty body fat percentage (-FAT). Cost reductions from crossbreeding systems were greater for ELA than for ELW or EWW, ranging from -3 to -5% for 2S, -6 to -7% for 2B and 2R, and -7 to -9% for 3S and 3R. Reductions in nonfeed costs were much greater than those in feed costs for EWW and ELW (-4 to -12% vs -2 to -4%), and especially for ELA (-9 to -17% vs -1 to -2%). Order of maternal trait importance in ranking breeds was NBA, VIAB, CR, MILK and -PUB for P, 2R and 3R systems and as maternal breeds in 2S and 3S systems. For cost of lean, -FAT was as important as NBA in all except maternal breed roles. For ELA, -DAYS was important in all breed roles, but not for EWW and ELW, especially in maternal breed roles. In ranking paternal breeds for use in 2S and 3S systems, the important traits were only VIAB for EWW, VIAB and -FAT for ELW, but VIAB, -FAT and -DAYS for ELA. Existing breeds ranked differently as paternal breeds than as maternal or general purpose breeds. Complementary paternal-maternal effects permitted greater cost reductions from best 3S (-7 to -10%) than from best 3R (-6 to -8%) breed combinations. Maternal breeds in crosses benefitted from superiority in components of both sow and pig performance.

Individual plus maternal heterotic effects on swine production were simulated with a bio-economic model by changing performance levels of eight traits:. –8 d in age at puberty, +3% in conception rate, +.94 in pigs born/litter, +.035 kg in pig birth weight, +2.05 Mcal·sow-1·d-1 in maximum milk output, +8% in preweaning survival, +10.8% in protein growth rate and +17.3% in fat growth rate. Associated heterosis simulated for other traits, such as weaning weights and postweaning gain/feed, was similar to experimental results. Effects of heterosis on biological (feed Mcal/kg) and economic ($/kg) costs were evaluated by simulating two- and three-breed crosses and purebred production. Pig heterosis reduced $/kg lean or $/kg live weight by 4% for marketing at 100 kg, and by 6% for $/kg of lean and 8% for $/kg of live weight for marketing at average 185-d weight. Sow heterosis reduced $/kg lean or $/kg live weight about 4%. Pig heterosis reduced feed Mcal/kg by only 1% and Mcal/kg live weight by 3%, and both were reduced only 1% by maternal heterosis. Traits that reduced litter costs/kg of output by increasing output/litter were responsible for most effects of heterosis on $/kg. However, heterosis in growth rate was important for feed Mcal/kg of lean marketed at 100 kg, and for feed Mcal/kg of live weight marketed at either 100 kg or at 185-d weight. Nonfeed costs/kg lean or live weight marketed at 100 kg were reduced more than feed costs by pig heterosis (–5 or –6 vs –2 or –3%) and by sow heterosis (–8 vs –1 or –2%). Effects of pig heterosis on nonfeed costs were increased to –12 or –14% by marketing at mean 185-d weight. Percentage reductions in total costs from heterosis were about one-third as large as corresponding increases in output/litter at market age.

Five sets of barrows from contemporary (C), genetically lean (L) and obese (O) phenotypes were used. The C pigs were crossbred Hampshire × Large White. The L and O pigs were crossbred Duroc × Yorkshire from lines selected for either low or high backfat thickness, respectively. The pigs were placed into adjustable cylindrical metabolism cages at 12 wk and again at 19 wk of age for 7-d adjustment and 4-d collection periods. Body weights of C, L and O pigs at 12-wk initial age were 32.9, 25.4 and 18.0 kg, respectively and at 19-wk initial age were 78.6, 55.0 and 39.7 kg, respectively. Pigs in each set consumed their daily feed allowance at the same percentage of their body weights and in two equal feedings. For 12-wk initial age period, daily weight gain (ADG) expressed as percentage of initial body weight was greater (P<.05) for C than for O pigs and was intermediate for L pigs. As determined by the total collection method, the percentage of retained nitrogen (RN) was similar (P>.05) for C and L pigs, but was less (P<.05) for O pigs. Coefficients of apparent metabolizable energy (ME) and N balance-corrected metabolizable energy (MEn) were similar (P>.05) among the three genotypes. The effect of genotypes on coefficients of RN, ME and MEn during the 19-wk initial age period showed the same trend as that during the 12-wk period. However, no difference was noted in ADG among the three genotypes. Apparent digestibilities of nitrogen (DN) and energy (DE) were also estimated by 4 N HCl-insoluble ash method. Genotype had no effect (P>.05) on coefficients of DN and DE for either the 12-wk or 19-wk period. Coefficients of DN and DE obtained by 4 N HCl-insoluble ash and total collection were similar (P>.05) at the 12-wk period, but were higher (P<.01) for the total collection method at the 19-wk period. It is concluded that the leaner C and L pigs retained more of ingested N, but that differences in weight gain and in energy and N retention among C, L and O pigs fed a standard grower diet are not related to digestibilities of dietary N and energy. Further, it is suggested that 4 N HCl-insoluble ash may be used as a natural indicator for estimating apparent nutrient digestibility in pigs, especially at younger ages.

A deterministic, bioeconomic simulation model of pork-production efficiency was used to predict effects of alternate management systems and feed prices on relative importance of several genetic traits for unspecialized swine populations. Traits considered were increased number born alive (NBA), preweaning viability (VIAB), growth rate (GR) and lean growth rate (LGR) and decreased age at puberty (−PUB), percentage fat at 100 kg (−%F) and fat growth rate (−FGR). Independent unit genetic standard deviation changes in the means of each trait were used to simulate effects on four measures of input/output efficiency (H): Mcal ME (metabolizable energy)/kg carcass lean (H1), Mcal ME/kg empty body weight (H2), cost/100 kg carcass lean (H3) and cost/100 kg live weight (H4). Management alternatives were length of farrowing interval, sale weight, marketing by weight or age and doubling feed prices. System efficiency was improved for all Himeasures by reducing farrowing interval from 192 to 157 d. Increasing sale weight reduced biological efficiency (H1and H2), but improved economic efficiency (H3and H4). Longer farrowing intervals or lower sale weights increased relative importance of reproductive traits and decreased importance of growth traits, but left ranking of traits unchanged. Marketing by age rather than weight permitted greater genetic improvement in economic efficiency from increased GR and LGR by spreading sow costs over more weight of pig or lean marketed, without increasing feed costs. Doubling feed prices decreased relative importance of NBA and VIAB for H3and H4 and magnified adverse effects of −%F, LGR and −FGR for H4. Optimal balance among breeding objectives will shift with future management-marketing systems.

A deterministic, bioeconomic computer model of pork production was used to predict effects on input/output efficiency (Hi) from increased conception rate (CR), number born alive (NBA), milk potential (MK), preweaning viability (VIAB), growth rate (GR),and lean growth rate (LGR) and from decreased age at puberty (−PUB), percentage fat at 100 kg (−%F) and fat growth rate (−FGR). Independent changes in the genetic means of each trait were used to simulate effects on feed ME (metabolizable energy) Mcal/kg carcass lean (H1), ME Mcal/kg empty body weight (H2), cost/100 kg carcass lean (H3) and cost/100 kg live weight (H4) under a continuous farrowing system with weaning at 28 d and marketing at 100 kg live wt. Relative values for traits in selection index construction expressed as percentage change in H1H2, H3and H4, respectively, per genetic standard deviation of change in each trait were: −.6, −.6, −.8, −.7 for −PUB; −.6, −.6, −1.5, −1.5 for NBA;−.7, −.6, −1.6, −1.5 for VIAB; −1.4, −.7, −.9, −.2 for GR; −3.8, −.7, −2.7, +.4 for −%F;−2.5, −.8, −1.7, 0 for LGR and −2.0, −.2, −1.3, +.5 for -FGR. Importance of GR, −%F, LGR, −FGR depends on price recognition of lean yield. Importance of NBA and VIAB was much greater for economic than for biological efficiency. Increased MK was useful only to realize maximum benefit from large increases in NBA, VIAB or GR. Responses of Hiper phenotypic standard deviation of change in each trait emphasized the great importance of NBA and VIAB levels for biological (H1and H2) and especially for economic (H3and H4) efficiency.

A deterministic computer model was constructed to simulate biological and economic inputs and outputs for life cycle pork production. Parameters and relationships used were developed and verified by comparison with experimental results in the literature. Driving variables are mean genetic potentials for lean growth rate, fat growth rate, preweaning viability, age at puberty, conception rate, number born alive, and maximum milk production, and management decisions (interval from first estrus to mating, maximum number of parities, rebreeding intervals, weaning age and marketing policy). Genetic potentials can differ between generations and subpopulations. Production inputs include metabolizable energy, crude protein, feed costs and fixed and variable nonfeed costs. Costs represent Midwestern environmentally regulated, slatted-floor farrowing and nursery units and modified-open-front finishing buildings. Production outputs include pigs and culled sows. The model calculates several measures of biological and economic efficiency, e.g., Mcal or dollar input/kg of live weight or of carcass lean outputs.

Effects of maternal heterosis on efficiency of postweaning growth and on carcass composition were evaluated in phase 2 of a comprehensive heterosis experiment by a comparison of two-breed cross steers from straightbred Hereford, Angus and Shorthorn cows with the three-breed cross steers from reciprocal crossbred cows. Time-constant postweaning gain, individual total digestible nutrient (TDN) conversion and carcass composition data were obtained on 134 three-breed and 84 two-breed cross steers born in 1963, 1964 and 1965. Postweaning efficiency was evaluated for TDN/GAIN from 227 kg to 408 kg of live weight and for age-constant carcass value minus postweaning feed cost.Three-breed cross steers from crossbred dams were 5.2% (P<01) heavier at the beginning but had no advantage in postweaning gain over two-breed cross steers from straightbred dams. This lack of a crossbred dam effect on postweaning gain was associated with slightly fatter carcasses with 4.0% (P<05) more kilograms of TDN required per kilogram of gain for three-breed crosses than for two-breed crosses. The extra weight at weaning and at the start of the test was maintained through the postweaning period and accounted for all of the $7.67 per head (3.5%, P<.05) advantage of three-breed crosses in age-constant carcass value less postweaning feed cost. This advantage did not take into account any difference in preweaning production costs for three-breed vs two-breed cross calves.