Results from nine generations of selection for increased litter size in swine

Direct selection for increased litter size was done for nine generations. The select line consisted of approximately 15 sires and 60 dams per generation, and selection was based on estimated breeding values for number of live pigs. A control line of approximately 10 sires and 30 dams was maintained with stabilizing selection. Heritabilities estimated in the select line using restricted maximal likelihood procedures, daughter-dam regression within sires, and half-sib analysis were 0.01, 0.04, and 0.00 for number of pigs born alive (NBA) and 0.02, 0.16, and 0.00 for total born per litter (TB). Corresponding estimates for the control line were 0.01, 0.06, and 0.23 and 0.02, 0.07, and 0.09 for NBA and TB, respectively. Realized heritabilities for NBA from multiple regression were 0.09 +/- 0.08 in the select line and 0.11 +/- 0.166 in the control line. Heritability estimated from regression of differences in response between lines on differences in cumulative selection differentials was 0.13 +/- 0.07. At Generation 9, litter sizes, estimated breeding values, and cumulative selection differentials were 0.86 (P < 0.05), 0.63 (P < 0.01), and 9.05 (P < 0.01) pigs larger for the select line than for the control line. Phenotypic differences between lines for TB, adjusted backfat (BF), and days to 104 kg (DAYS) were not significant. Genetic trends in the select line were 0.053 +/- 0.002 pigs/yr for NBA, 0.054 +/- 0.013 mm/yr for BF, and 0.398 +/- 0.110 d/yr for DAYS. Corresponding phenotypic trends were 0.145 +/- 0.051 pigs/yr, -0.012 +/- 0.089 mm per yr, and 0.307 +/- 0.278 d/yr, respectively. Genetic trends in the control line were -0.026 +/- 0.004 pigs/yr for NBA, 0.026 +/- 0.022 mm/yr for BF, and -0.532 +/- 0.182 d/yr for DAYS. Corresponding phenotypic trends were 0.001 +/- 0.085 pigs/yr, -0.043 +/- 0.147 mm/yr, and -0.519 +/- 0.462 d/yr, respectively. Litter size can be increased by direct selection using breeding values estimated from an animal model, in conjunction with rearing selected gilts in litters of 10 pigs or less.     

Correlated response in placental efficiency in swine selected for an index of components of lifter size

The objective of this study was to evaluate correlated response in placental efficiency to selection for components of litter size. Fourteen generations of selection had resulted in a difference between lines of three fully formed piglets at birth. Gilts from a line selected for an index of components of litter size (S, n = 33) and a randomly selected control (C, n = 27) were observed at farrowing. At delivery, the umbilical cord of each piglet was double tagged with identically numbered mouse ear tags to allow the piglet's weight to be matched to the corresponding placental weight. Litter size, placental weight, birth weight, and placental vascularity were recorded. Litter size was higher (12.0 +/- 0.7 vs 7.9 +/- 0.7) in S than in C (P < 0.001). Line differences in placental vascularity were not significant with or without adjustment for litter size (P = 0.45 and 0.39, respectively). Correlated response to selection for components of litter size resulted in a reduced birth weight (S 82.6% of C, P < 0.001) and a reduced placental weight (S 90.9% of C, P = 0.11). After adjusting for litter size, line differences in neither placental weight nor birth weight were significant (P = 0.40 and 0.07, respectively), which indicates that the reduction in birth weight was, for the most part, due to the increase in litter size. The result of the difference in the magnitude of the change for both weights was that placental efficiency, measured as the ratio of birth weight:placental weight was 0.43 higher in C (P = 0.05). Adjustment for litter size increased the difference in placental efficiency to 0.52 (P = 0.02). Since a significant difference in litter size favoring the selected line was observed, we hypothesize that this physiological response was achieved through mechanisms other than improved placental efficiency.     

Genetic parameters for reproduction and production traits of Landrace sows in Thailand

Data from Thai Landrace sows were used to estimate genetic parameters for reproduction and production traits in first and later parities. The reproduction traits investigated were total number of piglets born per litter (TB), number of stillborn piglets (SB), and number of piglets born alive but dead within 24 h (BAD). The reproduction data pertained to 12,603 litters born between 1993 and 2005. The production measures were ADG and backfat thickness (BF); these were recorded in 4,163 boars and 15,171 gilts. Analyses were carried out with a multivariate animal model using average information REML procedures. Heritability estimates of reproduction traits for first parity were 0.03 +/- 0.02 for TB, 0.04 +/- 0.02 for SB, and 0.06 +/- 0.02 for BAD. For later parities, they were 0.07 +/- 0.01 for TB, 0.03 +/- 0.04 for SB, and 0.02 +/- 0.01 for BAD. Heritability estimates for production traits were 0.38 +/- 0.02 for ADG and 0.61 +/- 0.02 for BF. Genetic correlations between ADG and TB tended to be favorable, and genetic correlations between BF and TB tended to be unfavorable in all parities. However, BF was genetically correlated unfavorably with SB in later parities, and the genetic correlations between TB and BAD tended to be unfavorable in all parities. The genetic correlations of TB, SB, and BAD between first and later parities were 0.85 +/- 0.13, 0.79 +/- 0.16, and 0.71 +/- 0.24, respectively. Selection for high growth rate will probably increase TB, and selection for low BF will decrease TB and increase SB. The results obtained also indicated that BAD will increase if there is selection pressure for high TB.     

Correlated responses for litter traits to six generations of selection for ovulation rate or prenatal survival in French Large White pigs

Effects of selection for reproductive traits were estimated using data from 3 pig lines derived from the same Large White population base. Two lines were selected for 6 generations on high ovulation rate at puberty (OR line) or high prenatal survival corrected for ovulation rate in the first 2 parities (PS line). The third line was an unselected control line. Genetic parameters for age and BW at puberty (AP and WP); number of piglets born alive, weaned, and nurtured (NBA, NW, and NN, respectively); proportions of stillbirth (PSB) and survival from birth to weaning (PSW); litter and average piglet BW at birth (LWB and AWB), at 21 d (LW21 and AW21), and at weaning (LWW and AWW) were estimated using REML methodology. Heritability estimates were 0.38 +/- 0.03, 0.46 +/- 0.03, 0.16 +/- 0.01, 0.08 +/- 0.01, 0.09 +/- 0.01, 0.04 +/- 0.01, 0.04 +/- 0.02, 0.19 +/- 0.02, 0.10 +/- 0.02, 0.10 +/- 0.02, 0.36 +/- 0.02, 0.27 +/- 0.01, and 0.24 +/- 0.01 for AP, WP, NBA, PSB, NW, NN, PSW, LWB, LW21, LWW, AWB, AW21, and AWW, respectively. The measures of litter size showed strong genetic correlations (r(a) >/= 0.95) and had antagonistic relations with PSB (r(a) = -0.59 to -0.75) and average piglet BW (r(a) = -0.19 to -0.46). They also had strong positive genetic correlations with prenatal survival (r(a) = 0.67 to 0.78) and moderate ones with ovulation rate (r(a) = 0.36 to 0.42). Correlations of litter size with PSW were negative at birth but positive at weaning. The OR and PS lines were negatively related to PSW and average piglet BW. Puberty traits had positive genetic correlations with OR and negative ones with PS. Genetic trends were estimated by computing differences between OR or PS and control lines at each generation using least squares and mixed model methodologies. Average genetic trends were computed by regressing line differences on generation number. Significant (P < 0.05) average genetic trends were obtained in OR and PS lines for AP (respectively, 2.1 +/- 0.9 and 3.2 +/- 1.0 d/generation) and WP (respectively, 2.0 +/- 0.5 and 1.8 +/- 0.5 d/generation) and in the PS line for NBA (0.22 +/- 0.10 piglet/generation). Tendencies (P < 0.10) were also observed for LWB (0.21 +/- 0.12 kg/generation) and AWW (-0.25 +/- 0.14 kg/generation) in the PS line. Selection on components of litter size can be used to improve litter size at birth, but result in undesirable trends for preweaning survival.     

Genetic evaluation of the ratio of calf weaning weight to cow weight

The phenotypic ratio of a calf's weaning weight to its dam's weight is thought to be an indicator of efficiency of the cow. Thus, the objectives of this research were to 1) estimate genetic parameters for the ratio of 200-d calf weight to mature-equivalent cow weight at weaning, its components, and other growth traits; and 2) evaluate responses to selection based on the ratio. Phenotypes evaluated were the ratio (100 kg/ kg; n = 4,184), birth weight (kg; n = 5,083), 200-d weight (kg; n = 4,902), 365-d weight (kg; n = 4,626), and mature-equivalent cow weight at weaning (kg; n = 4,375). In 1989, a randomly selected and mated control line and a line selected for greater values of the ratio were established. Average generation intervals were 3.39 +/- 0.05 and 3.90 +/- 0.08 yr in the ratio selected line and control line, respectively. The ratio selection line (n = 895) accumulated approximately 4.7 SD more selection differential than the control line (n = 912) over 2.5 generations. Data were analyzed with a multiple-trait Gibbs sampler for animal models to make Bayesian inferences. Heritability estimates (posterior mean +/- SD) for direct effects were 0.20 +/- 0.03, 0.46 +/- 0.04, 0.48 +/- 0.03, 0.58 +/- 0.04, and 0.76 +/- 0.02 for ratio, birth weight, 200-d weight, 365-d weight, and cow weight, respectively. Estimates for heritability of maternal effects were 0.58 +/- 0.05, 0.10 +/- 0.02, 0.13 +/- 0.02, and 0.10 +/- 0.02 for ratio, birth weight, 200-d weight, 365-d weight, respectively. Significant response to selection was limited to maternal effects: 1.32 +/- 0.38 ratio units per generation. As the ratio was a trait of the calf, estimated maternal genetic effects on the ratio contained both genetic effects due to dams that environmentally affected progeny performance and direct effects on the reciprocal of cow weight. In the control line, genetic trends in direct and maternal 200-d weight were -1.28 +/- 0.91 and 0.62 +/- 0.92 kg/generation, respectively, and the genetic trend in direct effects on cow weight was -5.72 +/- 2.80 kg/ generation. In the selection line, genetic trends in direct and maternal 200-d weight were 1.43 +/- 0.79 and 2.90 +/- 0.80 kg/generation and the genetic trend in cow weight was -2.79 +/- 2.43 kg/generation. Significant correlated responses were observed in direct effects on birth weight and maternal effects on 365-d weight. Results contraindicate use of the ratio of calf weaning weight to cow weight as a selection criterion.     

Genetic evaluation of an index of birth weight and yearling weight to improve efficiency of beef production

The CGC population is a stabilized composite of 1/2 Red Angus, 1/4 Charolais, and 1/4 Tarentaise germplasm. The objectives of this research were to estimate genetic parameters for weight traits of CGC and to evaluate genetic responses resulting from selection based on the following index: I = 365-d weight 3.2(birth weight). Phenotypes evaluated were birth weight (n = 5,083), 200-d weight (n = 4,902), 365-d weight (n = 4,626), and the index. In addition, there were 1,433 cows with at least one recorded weight, and 4,375 total observations of cow weight collected at the time their calves were weaned. In 1989, a randomly selected control line and a line selected for greater values of the index were established. Average generation intervals were 3.16 +/- 0.04 and 3.90 +/- 0.08 yr in the index and control lines, respectively. The index selection line (n = 950) accumulated approximately 212 kg more selection differential than the control line over three generations (n = 912). Heritability estimates for direct effects were 0.32 +/- 0.04, 0.49 +/- 0.05, 0.49 +/- 0.05, 0.30 +/- 0.04, and 0.70 +/- 0.04 for the index, birth weight, 365-d weight, 200-d weight, and cow weight, respectively. Heritability estimates for maternal effects were 0.05 +/- 0.02, 0.11 +/- 0.03, 0.04 +/- 0.02, and 0.19 +/- 0.04 for the index, birth weight, 365-d weight, and 200-d weight, respectively. In the control line, direct genetic changes for the index and its components were small. For the index selection line, direct genetic changes for the index, birth weight, 365-d weight, 200-d weight, and cow weight were 6.0 +/- 0.3, 0.45 +/- 0.09, 7.74 +/- 0.55, 3.42 +/- 0.25, and 6.3 +/- 0.9 kg/generation, respectively. Maternal genetic changes were generally small for both the control and index selection lines. Thus, selection for the index produced positive correlated responses for direct genetic effects on BW traits at all ages, with only minor effects on maternal genetic effects. Results demonstrate that despite a genetic antagonism that compromises selection response for decreased birth weight and increased postnatal growth, favorable genetic responses can be achieved with the selection index used in this study.     

Genetic variation of farrowing kinetics traits and their relationships with litter size and perinatal mortality in French Large White sows

Genetic parameters of litter traits and their relationships with farrowing kinetics traits were estimated in a Large White population to examine the impact of selection for litter size on perinatal mortality and one of its main determinants, farrowing kinetics. Data were collected on 2,947 farrowings from 1,267 sows between 1996 and 2004. Litter traits included the number born in total (NBT), number born alive (NBA), and the number (NSB) and proportion (PSB) of stillborn piglets. Four farrowing kinetics traits were considered: farrowing duration (FD), birth interval (BI = FD/NBT), heterogeneity of birth intervals (SDNB = SD of the number of piglets born each one-half hour), and birth assistance (BA) during the farrowing process. Genetic parameters were estimated using restricted maximum likelihood methodology. All traits were analyzed using a mixed linear animal model including year x month and parity as fixed effects; the additive genetic value of each animal and the sow permanent environment were treated as random effects. To normalize their distribution, kinetics traits were Box-Cox-transformed. Low heritability estimates were obtained for litter size and mortality traits, which was in agreement with literature results (i.e., 0.10 +/- 0.02, 0.08 +/- 0.02, 0.19 +/- 0.02, and 0.14 +/- 0.02 for NBT, NBA, NSB, and PSB, respectively). Heritability values were also low for kinetics traits: 0.10 +/- 0.02, 0.08 +/- 0.02, 0.01 +/- 0.01, and 0.05 +/- 0.03 for FD, BI, SDNB, and BA, respectively. The genetic correlation between NBT and NBA was strongly positive (ra = 0.90). On both phenotypic and genetic scales, NBT was positively associated with stillbirth (ra = 0.45 +/- 0.11, rp = 0.38 for NSB; ra = 0.46 +/- 0.13, rp = 0.17 for PSB). Conversely, NBA had low correlations with SB and PSB. Number born in total was moderately correlated to FD (ra = 0.34 +/- 0.15) and BI (ra = -0.37 +/- 0.15). A stronger relationship was found between NBA and BI (ra = -0.49 +/- 0.13), whereas the relationship with FD was lower (ra = 0.16 +/- 0.17). Moreover, FD was strongly correlated with stillbirth (ra = 0.42 +/- 0.12 with NSB), whereas BI was nearly independent of stillbirth. Contrary to selection on NBT, selection on NBA appears to be a good way to limit the negative side effects on stillbirth. Moreover, selection on NBA would lead to a small increase in FD and a faster and more regular birth process than would be obtained by selecting on NBT.     

The effect of divergent selection for uterine capacity on fetal and placental development at term in rabbits: maternal and embryonic genetic effects

The aim of this work was to study the effects of the genotype of the dam, the embryo, or their interactions on prenatal growth by performing double-reciprocal embryo transfers between two lines of rabbits divergently selected for uterine capacity. Females from high (n = 53) and low (n = 48) lines were slaughtered at 72 h of gestation, and recovered embryos were transferred to the oviducts of recipient does from the high (n = 23) and low (n = 19) lines. Each recipient doe received eight embryos from the high line into one oviduct and eight embryos from the low line into the other. Recipient does were slaughtered on d 28 of gestation. The percentages of live fetuses at 28 d of gestation were 89.2 and 74% for high and low recipient lines, respectively. Length and weight of the empty uterine horn and weight of the full uterine horn were not affected by either the recipient or by donor line. Fetal weight was affected by the recipient line but not by the donor line. Fetuses gestated in high recipient does were 7% heavier (P < 0.10) than those in the low recipient does. There was a donor and a donor x recipient interaction effect on fetal placental weight. Fetal placental weight was heavier (7%, P < 0.01) for embryos from the low line. Embryos from the high line gestated in low-line uteri showed a lower fetal placenta weight than did low-line embryos gestated in high-line uteri and low-line uteri (P < 0.05). Linear regression coefficients of fetal weight at term on fetal placental weights differed (P < 0.05) for the high and low donors (4.33 +/- 0.28 and 3.41 +/- 0.29 respectively). A significant effect of the donor genotype on individual placental length was observed (P < 0.05), which might have resulted from a smaller individual placental length of low-line embryos gestated high-line uteri (P < 0.10). Neither donor nor recipient lines affected maternal placental weight or available space for fetuses. Fetuses and their fetal placentae were heavier when receiving more than four blood vessels than when receiving less than three blood vessels (13 and 17% respectively, P < 0.05). Neither recipient nor donor genotype affected the number of blood vessels arriving at each live fetus. Thus, fetal weight depends on the maternal genotype, whereas fetal placental weight depends on the embryo genotype in these two lines of rabbits divergently selected for uterine capacity.     

Genetic parameters and trends for production traits and their relationship with litter traits in Landrace and Yorkshire pigs

Genetic parameters and trends in the average daily gain (ADG), backfat thickness (BF), loin muscle area (LMA), lean percentage (LP), and age at 90 kg (D90) were estimated for populations of Landrace and Yorkshire pigs. Additionally, the correlations between these production traits and litter traits were estimated. Litter traits included total born (TB) and number born alive (NBA). The data used for this study were obtained from eight farms during 1999 to 2016. Analyses were carried out with a multivariate animal model to estimate genetic parameters for production traits while bivariate analyses were performed to estimate the correlations between production and litter traits. The heritability estimates were 0.52 and 0.43 for ADG; 0.54 and 0.45 for BF; 0.25 and 0.26 for LMA; 0.54 and 0.48 for LP; and 0.56 and 0.46 for D90 in the Landrace and Yorkshire breeds, respectively. The ADG and D90 showed low genetic correlation with BF and LP. The LMA had ?0.40, ?0.32, 0.49, and 0.39 genetic correlations with ADG, BF, LP, and D90, respectively. Genetic correlations between production and litter traits were generally low, except for the correlations between LMA and TB (?0.23) in Landrace and ADG and TB (?0.16), ADG and NBA (?0.18), D90 and TB (0.19), and D90 and NBA (0.20) in Yorkshire. Genetic trends in production traits were all favorable except for LMA.     

Pregnancy-specific protein B (bPSPB) and progesterone monitoring of post-partum dairy cows with placental retention

The relationship between placental retention, progesterone and pregnancy-specific protein B (bPSPB) was determined in 60 calving Holstein cows. The cows were divided into two groups with placental retention (WPR, n = 16) and no placental retention (NPR, n = 44). Every 4 days, until 60 days post-partum, blood samples were taken and the uteri were checked using ultrasonographv. The puerperal characteristics of NPR and WPR were as follows: mean days of abnormal vaginal discharge: 20.2+/-5 versus 35.6+/-7 (P < 0.01); mean intervals to uterine involution: 21.4+/-3.7 versus 27.6+/-7.6 days (P < 0.01); rate of endometritis: 25 versus 100% (P < 0.01). The mean numbers of oestrus cycles per cow were 1.75+/-0.5 versus 0.85-/+0.9 (P < 0.05) and the mean durations of the first oestrus cycle were 18+/-3.5 versus 16+/-2.1 days (P > 0.05). The mean intervals to first ovulation were 21.5+/-8.4 versus 35+/-19 days (P < 0.01). bPSPB blood concentrations were higher in the WPR group at calving with 955+/-170 versus 750+/-205 ng/ml (P < 0.01) and also during the first 32 days post-partum with 173.68+/-47.3 versus 131.0+/-29.2 ng/ml (P < 0.01). The mean bPSPB half-life was similar in the two groups: 6.9+/-2.5 versus 6.5+/-2.1 days (P > 0.05). In conclusion, it was found that placental retention was associated with a higher rate of endometritis, a lower number of cycles, longer interval to first post-partum ovulation and higher concentration of bPSPB at calving and during the post-partum period. The positive relationship between bPSPB concentrations and calf birth weight and their association with post-partum pathological events may be useful in monitoring animals presenting high concentrations at calving.     

The role of altered uterine-embryo synchrony on conceptus growth in the pig

This study was conducted to determine whether inducing an embryo-uterine asynchrony during the preimplantation period would alter fetal and(or) placental size at term. Yorkshire gilts (n = 24) were checked twice daily for estrus and bred to a Yorkshire boar 24 h after the first exhibition of estrus. Embryos (1 to 4 cells) were flushed from the oviducts of each donor gilt on d 2.5 of gestation and transferred in equal numbers to the oviducts of a recipient gilt on d 1.5, 2.5, or 3.5 of the estrous cycle. Gilts were slaughtered on d 112 of gestation (calculated on the age of the conceptus) and fetal and placental weight, placental surface area, and implantation site lengths were determined. Although litter sizes were similar (9.1+/-0.9), conceptuses transferred to d 3.5 recipients became heavier fetuses (1.44+/-0.05 vs 1.23+/-0.04 kg, P < 0.001), with larger placental surface areas (1,793+/-60 vs 1,459+/-43 cm2, P < 0.01), and longer implantation sites (32.1+/-1.5 vs 24.9+/-0.6 cm, P < 0.001) than those transferred to recipients on d 2.5. These data demonstrate that oviductal transfer of embryos into a reproductive tract that is more advanced by as little as 24 h can result in alterations in placental growth and function during gestation.     

Responses to 19 generations of litter size selection in the NE Index line. II. Growth and carcass responses estimated in pure line and crossbred litters

Our objective was to estimate responses in growth and carcass traits in the NE Index line (I) that was selected for 19 generations for increased litter size. Differences between Line I and the randomly selected control line (C) were estimated in pure line litters and in F1 and three-way cross litters produced by mating I and C females with males of unrelated lines. Contrasts of means were used to estimate the genetic difference between I and C and interactions of line differences with mating type. In Exp 1, 694 gilts that were retained for breeding, including 538 I and C and 156 F1 gilts from I and C dams mated with Danbred NA Landrace (L) sires, were evaluated. Direct genetic effects of I and C did not differ for backfat (BF) at 88.2 kg or days to 88.2 kg; however, I pigs had 1.58 cm2 smaller LM area than did C pigs (P < 0.05). Averaged over crosses, F1 gilts had 0.34 cm less BF, 4.29 cm2 greater LM area, and 31 d less to 88.2 kg than did pure line gilts (P < 0.05). In Exp 2, barrows and gilts were individually penned for feed intake recording from 27 to 113 kg and slaughtered. A total of 43 I and C pigs, 77 F1 pigs produced from pure line females mated with either L or Danbred NA 3/4 Duroc, 1/4 Hampshire boars (T), and 76 three-way cross pigs produced from F1 females mated with T boars were used. Direct genetic effects of I and C did not differ for ADFI, ADG, G:F, days to 113 kg, BF, LM area, ultimate pH of the LM, LM Minolta L* score, or percentage of carcass lean. Interactions of line effects with crossing system were significant only for days to 113 kg. Pure line I pigs took 4.58+/-4.00 d more to reach 113 kg than did C pigs, whereas I cross F1 pigs reached 113 kg in 6.70+/-3.95 d less than C cross F1 pigs. Three-way cross and F1 pigs did not differ significantly for most traits, but the average crossbred pig consumed more feed (0.23+/-0.04 kg/d), gained more BW per unit of feed consumed (0.052+/-0.005 kg/kg), grew faster (0.20+/-0.016 kg/d), had less BF (-0.89+/-0.089 cm), greater LM area (5.74+/-0.926 cm2), more lean (6.21+/-0.90%), and higher L* score (5.27+/-1.377) than the average pure line pig did (P < 0.05). Nineteen generations of selection for increased litter size produced few correlated responses in growth and carcass traits, indicating these traits are largely genetically independent of litter size, ovulation rate, and embryonic survival.     

Estimating genetic differences in natural resistance in Rhön and Merinoland sheep following experimental Haemonchus contortus infection

Genetic parameters of natural resistance were estimated in Rh?n and Merinoland (German Merino) sheep following experimental infection with Haemonchus contortus. A total of 133 Rh?n and 244 Merinoland lambs descending from 5 and 6 rams, respectively, were evaluated. Each helminth-naive lamb was orally infected with 5000 infective third-stage larvae (L(3)) of the nematode H. contortus at 12 weeks of age. Faecal egg counts (FEC) and haematocrit values were measured in all lambs at 16 and 20 weeks of age. Seventy-nine Merinoland and 29 Rh?n male lambs were slaughtered immediately after the second sampling and worms were collected. Mean worm burden was calculated and the length of adults worms from an aliquot was measured.FEC of Rh?n sheep was higher compared with Merinoland sheep (P<0.01). H. contortus L(3)-larvae specific antibody (IgL) level was higher in Rh?n sheep (P<0.05). However, no differences in haematocrit, worm burden and IgG antibody values could be found between the breeds. Heritabilities for log FEC (+/-S.E.) were 0.0 and 0.07 (+/-0.07) for the first sample in Rh?n and Merinoland sheep, respectively. Values for the second sample were higher in both breeds (Rh?n 0.35+/-0.14, P<0.05; Merinoland 0.17+/-0.07, P<0.05). Corresponding heritabilities for haematocrit were higher in Merinoland (0.56+/-0.20 and 0.51+/-0.27) compared with Rh?n (0.29+/-0.12 and 0.08+/-0.13). Heritabilities for worm burden were high in Rh?n (0.54+/-0.2) and low in Merinoland (0.06+/-0.14 and 0.11+/-0.15). Estimated values for IgL were between 0.13 (+/-0.11) for the first sample in both breeds and 0.30 (+/-0.18) for the second sample in Rh?n sheep. Corresponding heritabilities for IgG were not different from 0.0 in both breeds (P>0.05). Positive phenotypic correlations were estimated for IgG and IgL values in both breeds (P<0.01). IgG was significantly (P<0.05) and positively correlated with worm burden in male Merinoland and IgL with worm burden in male Rh?n sheep.     

Direct responses to six generations of selection for ovulation rate or prenatal survival in Large White pigs

Effects of selection for ovulation rate or prenatal survival were examined using data from 3 pigs lines derived from the same base Large White population. Two lines were selected for 6 generations on high ovulation rate at puberty (OR line) or high prenatal survival corrected for ovulation rate in the first 2 parities (PS line). The third line was an unselected control line. Genetic parameters for ovulation rate on the left, right, and both ovaries at puberty (ORPL, ORPR, and ORP, respectively) and at fertilization (ORFL, ORFR, and ORF, respectively), total number of piglets born (TNB) per litter, prenatal survival (PS = TNB/ORF), and PS corrected for ovulation rate (CPS = PS + 0.018ORF) were estimated using REML methodology. Responses to selection were estimated by computing differences between OR or PS and control lines at each generation using least squares and mixed models methodology. Average genetic trends were computed by regressing line differences on generation number. Realized heritabilities were estimated using standard procedures. Heritability estimates were 0.17, 0.11, 0.34, 0.13, 0.09, 0.33, 0.14, 0.11, and 0.17 (SE = 0.01 to 0.03) for ORPL, ORPR, ORP, ORFL, ORFR, ORF, PS, CPS, and TNB, respectively. Realized heritabilities were 0.37 +/- 0.08 and 0.10 +/- 0.09 for ORP and CPS, respectively. The different measures of ovulation rate had strong genetic correlations (r(g) > 0.7). The ORF had midrange negative genetic correlations with PS and CPS (-0.45 +/- 0.07 and -0.42 +/- 0.08, respectively). The ORP also had an antagonistic genetic relationship with PS (-0.26 +/- 0.07) but was almost independent from CPS (-0.02 +/- 0.11). The TNB was moderately correlated with ORP and ORF (r(g) = 0.41 +/- 0.09 for both traits). Average genetic trends in OR and PS lines were, respectively, 0.49 +/- 0.10 and 0.11 +/- 0.10 for ORP, and 0.43 +/- 0.11 and 0.11 +/- 0.11 for ORF. Responses to selection were slightly superior in the left than in the right ovary. No significant difference was found for PS or CPS in any of the lines. The TNB did not change in the OR line but significantly improved in the PS line (0.24 +/- 0.11 piglets/generation).     

Correlated responses in reproductive and carcass traits to selection for 200-day weight in Duroc swine.

Correlated responses in reproductive and carcass traits from a line of Duroc pigs selected for increased 200-d weight along with a randomly selected control line were studied in 189 litters (116 select, 73 control) and 191 pigs (106 select, 85 control), respectively. Reproductive and maternal traits studied included litter sizes born, born alive, and alive at 21 d and litter weight at birth and at 21 d. Carcass traits studied were carcass length, longissimus muscle area, average backfat thickness, 10th rib backfat thickness, specific gravity, weights of closely trimmed ham, loin, and shoulder, belly weight, subjective scoring of the longissimus muscle for color and marbling, estimated percentage of muscle and lean gain per day. Total weighted cumulative selection differential for 200-d weight was 81.7 kg. The realized heritability for 200-d weight was .18 +/- .08, and the change in 200-d weight was 2.5 +/- 1.2 kg per generation. The regression coefficient of litter size born on generation was -.29 +/- .12 (P less than .10) pigs per generation. None of the other regression coefficients for the reproductive traits differed from zero. Average backfat thickness, 10th rib backfat thickness, and belly weight increased by .093 +/- .016 cm, .122 +/- .029 cm, and .089 +/- .040 kg, respectively, per generation. Specific gravity, ham weight, shoulder weight, color score, and percentage of muscle decreased -.00086 +/- .00024, -.165 +/- .013 kg, -.104 +/- .011 kg, -.035 +/- .015 points, and -.47 +/- .12%, respectively, per generation in response to the selection.(ABSTRACT TRUNCATED AT 250 WORDS)     

Correlated responses in growth, carcass, and meat quality traits to divergent selection for testosterone production in pigs

The objective of this project was to characterize changes in growth, carcass yield, and meat quality traits in castrates and gilts in response to divergent selection for testosterone production. In generation 21, endogenous testosterone concentrations in Duroc boars of the high (HTL) and low (LTL) testosterone lines averaged 49.0 and 27.8 ng/mL (P < 0.01), respectively. Eight LTL and 10 HTL boars were used to sire 29 LTL and 33 HTL litters. To remove the effects of inbreeding, these same boars were mated to females of a Large White x Landrace composite (WC) to generate 11 WC by LTL litters (WLT) and 23 WC by HTL litters (WHT). Castrates and gilts were then allotted to LTL (n = 53), HTL (n = 61), WLT (n = 102), and WHT (n = 101) for testing. Growth and carcass traits analyzed included days to 114 kg (D114), ADG, backfat adjusted to 114 kg (ABF), LM area adjusted to 114 kg and predicted percent lean (PPL). Fat-O-Meater data collected were adjusted fat depth (AFD), adjusted loin depth, and percent lean. Meat quality traits characterized at 24 h postmortem included marbling score, percent lipid, pH, drip loss, color score, and Minolta L*, a*, and b*. Data were analyzed with a mixed model including fixed effects of line, mating type (purebred or crossbred), sex, and the random effect of sire nested within line. All possible interactions among fixed effects were tested. The HTL had fewer D114 (P < 0.05), greater ADG (P < 0.01), greater ABF (P < 0.01), and lower PPL (P < 0.01) than LTL. The WHT and WLT did not differ for D114, ADG, or ABF. The WHT had smaller LM area adjusted to 114 kg (P < 0.05) and greater drip loss (P < 0.05) than WLT. The WLT had lower adjusted loin depth (P < 0.05) than LTL and HTL. The LTL and HTL had greater subjective scores for marbling (P < 0.05) compared with WLT and WHT. The least squares mean for percent lipid for HTL and LTL was 4.00. The WHT had greater means for L*, a*, and b* (P < 0.05) than WLT. Pigs selected for increased testosterone production grew faster and produced fatter carcasses than pigs selected for decreased testosterone. Changes in growth, carcass yield, and meat quality traits were detected in castrates and gilts in response to divergent selection for testosterone production.     

Genetic correlations between two strains of Durocs and crossbreds from differing production environments for slaughter traits

The aim of this study was to estimate the genetic correlations between 2 purebred Duroc pig populations (P1 and P2) and their terminal crossbreds [C1 = P1 x (Landrace x Large White) and C2 = P2 x (Landrace x Large White)] raised in different production environments. The traits analyzed were backfat (BF), muscle depth (MD), BW at slaughter (WGT), and weight per day of age (WDA). Data sets from P1, P2, C1, and C2 included 26,674, 8,266, 16,806, and 12,350 animals, respectively. Two-trait models (nucleus and commercial crossbreds) for each group included fixed (contemporary group, sex, weight, and age), random additive (animal for P1 and P2 and sire for C1 and C2), random litter, and random dam (C1 and C2 only) effects. Heritability estimates (+/-SE) for BF were 0.46 +/- 0.04, 0.38 +/- 0.02, 0.32 +/- 0.02, and 0.33 +/- 0.02 for P1, P2, C1, and C2, respectively. Heritability estimates for MD were 0.31 +/- 0.01, 0.23 +/- 0.02, 0.19 +/- 0.01, and 0.12 +/- 0.01 for P1, P2, C1, and C2, respectively. The estimates for WGT and WDA were 0.31 +/- 0.01, 0.21 +/- 0.02, 0.16 +/- 0.01, and 0.18 +/- 0.01 and 0.32 +/- 0.01, 0.22 +/- 0.02, 0.16 +/- 0.01, and 0.19 +/- 0.01, respectively. Genetic correlations between purebreds and crossbreds for BF were 0.83 +/- 0.09 (P1 x C1) and 0.89 +/- 0.05 (P2 x C2), for MD 0.78 +/- 0.05 (P1 x C1) and 0.80 +/- 0.08 (P2 x C2). For WGT and WDA, the correlations were 0.53 +/- 0.08 (P1 x C1), 0.80 +/- 0.10 (P2 x C2), and 0.60 +/- 0.07 (P1 x C1) and 0.79 +/- 0.09 (P2 x C2), respectively. (Co)variances in crossbreds were adjusted to a live BW scale. Compared with purebreds, the genetic variances in crossbreds were lower, and the residual variances were greater. Sire variances in crossbreds were approximately 20 to 30% of the animal variances in purebreds for BF and MD but were 13 to 25% for WGT and WDA. The efficiency of purebred selection on crossbreds, assessed by EBV prediction weights, ranged from 0.43 to 0.91 for line 1 and 0.70 to 0.92 for line 2. When nucleus and commercial environments differ substantially, the efficiency of selection varies by line and traits, and selection strategies that include crossbred data from typical production environments may therefore be desirable.     

Correlated responses in reproductive and carcass traits to selection for 70-day weight in Landrace swine.

Correlated responses in reproductive and carcass traits were studied in 181 litters and 218 pigs from a line of Landrace pigs selected six generations for increased weight at 70 d of age and a contemporaneous, randomly selected control line. The reproductive and maternal traits studied included litter sizes born, born alive, and alive at 21 d and litter weight at birth and at 21 d. Carcass traits studied were carcass length, longissimus muscle area, average backfat thickness, 10th-rib backfat thickness, specific gravity, weights of closely trimmed ham, loin, and shoulder, belly weight, subjective scoring of the longissimus muscle for color and marbling, estimated percentage of muscle, and lean gain per day. Total weighted cumulative selection differential for 70-d weight was 30.2 kg. The realized heritability for 70-d weight was .13 +/- .06, and the change in 70-d weight was .65 +/- .29 kg per generation. The regression coefficient of litter size at 21 d on generation was .24 +/- .10 (P less than .10) pigs per generation. None of the other regression coefficients for the reproductive traits differed from zero. Carcass length, specific gravity, and ham weight decreased (P less than .10) -.075 +/- .036 cm, -.00054 +/- .00027, and -.102 +/- .048 kg, respectively, per generation. Color score and lean gain per day increased .046 +/- .021 points and .0032 +/- .0013 kg/d, respectively, each generation in response to the selection.(ABSTRACT TRUNCATED AT 250 WORDS)     

Direct and correlated responses to selection for efficiency of lean gain in mice

Improvement in feed efficiency when selection is based on gain:feed ratio has often been accompanied by a reduction in feed intake. The following four criteria were used in mass selection for improved lean gain efficiency in mice with an objective of evaluating changes in lean gain and intake: 1) gain deviation, animals selected had the greatest gain in fat-free mass (FFM) after adjustment to a constant intake; 2) intake deviation, mice selected had the least feed intake after adjustment to a constant gain in FFM; 3) intrinsic efficiency, similar to the second criterion except that adjustment was also made for average weight maintained during the period; and 4) a positive control that used the ratio of gain in FFM: feed intake as the selection criterion. A fifth line, in which a male and a female were selected at random from each litter, served as a negative control. Experimental animals were outbred mice of the CF1 strain. Two replicates of the five lines were included in the study. Twelve males and females were pair-mated within each line-replicate combination each generation. Feed disappearance was measured from 25 to 42 d. Mice were scanned to obtain an electrical conductivity measurement for prediction of FFM. After six generations of selection, realized heritabilities for gain:feed, gain deviation, intake deviation, and intrinsic efficiency were .00 +/- .04, .04 +/- .29, .35 +/- .08, and .28 +/- .06, respectively. There were no differences among lines for gain:feed ratio. The correlated response in feed intake reduction was significant in the intake deviation and intrinsic efficiency lines (-.17 +/- .05 and -.21 +/- .04 g x d(-1) x generation(-1), respectively). The realized genetic correlations between the ratio and gain deviation, intake deviation, and intrinsic efficiency were .83 +/- .15, .01 +/- .04, and .21 +/- .12, respectively. Litter size was depressed in all selected lines.     

Correlated response to selection for litter size in pigs: II. Carcass,meat, and fat quality traits

Data on a pig line selected for litter size (H) and a control line (C) were used to estimate the correlated responses to litter size in carcass, meat, and fat quality traits. The differences between the genetic means of animals from line H and line C were used to estimate correlated responses. No differences were found between the two lines in carcass measurements except backfat depth, which was higher (P < 0.05) in line H (0.69 +/- 0.28 mm). This led to a decrease (P < 0.05) in predicted carcass lean content (-6.0 +/- 2.7 g/kg). Differences in joint weight distribution between lines were primarily due to belly weight, which was higher (P < 0.05) in line H (6.3 +/- 1.2 g/kg). There were no important changes in meat quality traits. Chemical composition of semimembranosus muscle (SM) and subcutaneous backfat (SB) differed between lines only for DM in SB, which was higher (P < 0.05) in line H (15.1 +/- 7.1 mg/g), and for the fatty acid composition of intramuscular fat. The fatty acid profile in line H showed a lower (P < 0.01) proportion of polyunsaturated fatty acids (-14.7 +/- 4.8 mg/g FA), particularly with regard to the content of linoleic acid (-12.5 +/- 3.9 mg/g FA). It is concluded that selection for litter size reduced the lean content in the carcass but the proportion of high-priced cuts and meat quality traits were not affected. However, selection may lead to changes in the composition of intramuscular fat lipids towards a lower content of polyunsaturated fatty acids. The observed correlated effects can be interpreted assuming that selected pigs are more mature at the same weight, though the underlying genetic and physiologic processes that cause them are unknown. The results of this experiment indicate that the metabolic pathways taking part in fat metabolism should be considered first.