R. K. Johnson

Selection for components of reproduction in swine

Abstract The response per generation to 10 generations of mass selection for ovulation were 0.49 ova, −1.6% in embryo survival and 0.06 piglets per litter at birth. Line differences (select-control) in generation 9 and 10 gilts and sows ranged from 3.4 to 5 ova. Control line gilts and sows had 5.4 to 10.6% higher embryo survival to days 30 and 70 of gestation than did select line females. One generation of random selection followed by four generations of litter size selection, selection for decreased age at puberty or relaxed ovulation rate selection in the high ovulation rate line has resulted in lines that differed from the control line in litter size at birth by 0.78 ± 0.22, 0.37 ± 0.39 and 0.84 ± 0.52 pigs per litter at first, second and third parity, respectively. These results were used to derive a selection index to increase litter size by selection for its components (ovulation rate, OR, and embryo survival, ES). A technique of selection based on laparotomy to increase the number of females tested with a given set of farrowing places is presented. Rate of response in LS from use of the selection index, I = 10.6 OR + 72.6 ES, in a population of 40 farrowing females and 15 males per generation, is expected to increase litter size 2.5 times faster than selection on LS due to higher selection intensity and optimum emphasis on the component traits.

Factors associated with sow stayability in 6 genotypes.

The purpose of this study was to determine the association of production factors with stayability to parity 4 (STAY4) under controlled experimental conditions. Data were from 2,293 female pigs, sampled from 6 genetic lines that were entered into the National Pork Producers Council Maternal Line National Genetic Evaluation Program. Genetic lines evaluated included Newsham (NH), National Swine Registry (NSR), American Diamond Swine Genetics (ADSG), Danbred (DAN), and 2 Dekalb-Monsanto lines (DK44 and GPK347). Stepwise logistic regression was utilized in the analysis of STAY4. All effects were nested within genetic line. Categorical effects in the model were arrival date to the wean-to-finish unit (entry date) and breed-gestation-farrowing facility (farm). Continuous effects in the model were gilt backfat, LM depth, ADG, age at puberty, age at first farrowing, and traits recorded before the last litter of the sow (prefarrow backfat, number born alive, number weaned, litter weaning weight, lactation feed intake, lactation backfat loss, and lactation length). Factors significant for STAY4 included farm, entry date, age at first farrowing, ADG, gilt backfat, and lactation before removal effects, as well as feed intake, number born alive, and lactation length. Age at first farrowing and lactation feed intake affected all genetic lines. Regression coefficients for STAY4 on age at first farrowing were -0.014, -0.022, -0.017, -0.016, -0.011, and -0.021 (all P < 0.05), respectively, for NH, NSR, ADSG, DK44, GPK347, and DAN genetic lines. Regression coefficients for STAY4 on lactation feed intake were 0.043, 0.049, 0.051, 0.061, 0.120, and 0.097 (all P < 0.05), respectively, for NH, NSR, ADSG, DK44, GPK347, and DAN females. Age at puberty, age at first farrowing, and lactation feed intake had the greatest effect on STAY4.

Estimation of genetic parameters for average daily gain using models with competition effects.

Components of variance for ADG with models including competition effects were estimated from data provided by the Pig Improvement Company on 11,235 pigs from 4 selected lines of swine. Fifteen pigs with average age of 71 d were randomly assigned to a pen by line and sex and taken off test after approximately 89 d (off-test BW ranged from 61 to 158 kg). Models included fixed effects of line, sex, and contemporary group and initial test age as a covariate, with random direct genetic, competition (genetic and environmental), pen, litter, and residual effects. With the full model, variances attributable to direct, direct-competition, genetic competition, and litter (co)variance components could be partitioned; genetic competition variance was small but statistically significantly different from zero. Variances attributable to environmental competition, pen, and residual effects could not be partitioned, but combinations of these environmental variances were estimable. Variances could be partitioned with either pen effects or environmental competition effects in the model. Environmental competition effects seemed to be the source of variance associated with pens. With pen as a fixed effect and without environmental competition effects in the model, genetic components of variance could not be partitioned, but combinations of genetic (co)variances were estimable. With both pen and environmental competition effects ignored, estimates of direct-competition and genetic competition (co)variance components were greatly inflated. With competition (genetic and environmental) effects ignored, the estimate of pen variance increased by 39%, with little change in estimates of direct genetic or residual variance. When both pen and competition (genetic and environmental) effects were dropped from the model, variance attributable to direct genetic effects was inflated. Estimates of variance attributable to competition effects were small in this study. Including environmental competition effects as permanent environmental effects in the model did not change estimates of genetic (co)variances. We concluded that including either pen effects or environmental competition effects as random effects in the model avoids bias in estimates of genetic variances but that including pen effects is much easier.

Identifying putative candidate genes and pathways involved in immune responses to porcine reproductive and respiratory syndrome virus (PRRSV) infection

Differences in gene expression were compared between RNAs from lungs of high (HR) and low (LR) porcine reproductive and respiratory syndrome virus (PRRSV) burden pigs using the swine protein-annotated long oligonucleotide microarray, the Pigoligoarray. Pathway analyses were carried out to determine biological processes, pathways and networks that differ between the LR and HR responses. Differences existed between HR and LR pigs for 16 signalling pathways [P < 0.01/-log (P-value) >1.96]. Top canonical pathways included acute phase response signalling, crosstalk between dendritic cells and natural killer cells and tight junction signalling, with numerous immune response genes that were upregulated (SOCS1, SOD2, RBP4, HLA-B, HLA-G, PPP2R1A and TAP1) or downregulated (IL18, TF, C4BPA, C1QA, C1QB and TYROBP). One mechanism, regulation of complement activation, may have been blocked in HR (PRRSV-susceptible) pigs and could account for the poor clearance of PRRSV by infected macrophages. Multiple inhibiting signals may have prevented effective immune responses in susceptible HR pigs, although some protective genes were upregulated in these pigs. It is likely that in HR pigs, expression of genes associated with protection was delayed, so that the immune response was not stimulated early; thus, PRRSV infection prevented protective immune responses.

Generation and sequence characterization of a normalized cDNA library from swine ovarian follicles

Ovulation rate is a major factor determining litter size in swine and is, therefore, a trait of economic importance to the pork industry. The dynamics of follicle development, which in turn are dictated by a balance between follicle recruitment, maturation, selection, and atresia, are a major determining factor of ovulation rate. The role of several genes expressed in the ovaries during these processes has been described, but studies utilizing large-scale genomic approaches have yet to be conducted to examine gene expression in this tissue more globally. We have developed a normalized cDNA library from swine ovarian follicles in various stages of development, ranging from 2.0 to 10.0 mm in diameter, collected from gilts from divergent genetic lines selected for high and low ovulation rates, during the 7 initial days of the follicular phase of the estrous cycle. EST sequences were obtained from 5231 distinct clones derived from this library. In total, 3479 unique sequence clusters were obtained, of which 2661 singletons (76.5%) were observed. BLASTN searches with the primary sequences from the clusters obtained resulted in 1037 sequences not matching (E <1.0?06) any of the sequences in the nt database (29.8% novelty rate). This resource will facilitate the use of cDNA microarrays in functional genomics studies aiming at unraveling the genetic and physiological mechanisms underlying follicle maturation and ovulation rate in swine.

Genetic analysis of rebreeding intervals, litter traits, and production traits in sows of the National Czech nucleus

Abstract Weaning to service (WTS), weaning to conception (WTC) and weaning to farrowing (WTF) intervals of 2896 Large White and Landrace sows of the National Czech nucleus herds were used to evaluate genetic relationships with litter and production traits. Univariate and bivariate analyses were used to estimate genetic and environmental parameters using a restricted maximum likelihood method. Data were adjusted for significant fixed effects and covariates. Univariate analyses were done with and without maternal effects in models. Maternal effects were found to be important for litter weight and backfat and were included in bivariate analyses with these traits. In a second analysis, phenotypic interval distributions were regarded as a mixture of normal and exponential distributions and evaluated with an extended maximum likelihood algorithm. Contrasts of average breeding values (EBV) for the other traits between sows with normal and prolonged intervals were estimated. Direct heritabilities for WTS, WTC, and WTF were, respectively, 0.12, 0.08, and 0.08. Maternal heritabilities were near zero for all traits except litter weight ( h m 2 = 0.05) and backfat ( h m 2 = 0.06). Genetic correlations of intervals with other traits were between −0.20 and 0.20, and the correlation between WTS and WTC was 0.93. Common environmental effects on repeated sow rebreeding intervals and reproductive traits were small, but common environmental effects of litter of origin were important for backfat and average daily gain ( c 2 = 31 and 58%, respectively). Variance components for WTC and WTF were similar. Combined EBV contrasts for backfat (BF), litter weight-maternal, total number born, and number born alive for WTS were significant and had the same sign as the genetic correlations. Selection for litter weight and BF may cause prolonged intervals, but genetic relationships are not strong.

Effects of restricting energy during the gilt developmental period on growth and reproduction of lines differing in lean growth rate: responses in feed intake, growth, and age at puberty.

The overall objective was to compare reproductive performance through 4 parities of gilts developed with ad libitum access to feed or with restriction of energy to 75% of ad libitum intake. Effects on growth and pubertal development are reported. The experiment was a 2 × 2 factorial with 661 gilts. One-half of the gilts (n = 330) were allowed ad libitum access to feed from weaning to breeding at 235 d of age (AL), and 331 littermates were developed with ad libitum access to feed to 123 d of age and then restricted to 75% of ad libitum intake to 235 d of age (Res). Diets for gilts on regimen AL were formulated to meet requirements for growth. All nutrients except energy and selenium were increased in the diet fed to gilts on regimen Res so that nutrient intake per unit of BW was expected to be similar to that of gilts on regimen AL. Sires of all gilts were from an industry maternal line. Dams were either an industry Large White-Landrace cross, or Nebraska selection Line 45, producing gilts denoted as LW/LR and L45X, respectively. Traits were recorded every 2 wk. Recording of feed intake and BW began at 53 d of age, and recording of backfat (BF) and LM area (LMA) began at 123 d of age. Estrus detection began at 140 d of age to determine age at puberty (AP). The G:F ratio from 123 to 235 d of age for gilts on the AL regimen was greater (0.269 vs. 0.257, P < 0.01) than for gilts on the Res regimen; the greatest difference occurred in the first 2-wk period following feed restriction. The LW/LR gilts were heavier, had less BF, and had greater LMA than L45X gilts, but interactions with feeding regimen and period of development existed. Feed restriction reduced BW, BF, LMA, and ratio of BF to BW, but had little effect on ratio of LMA to BW. More L45X gilts than LW/LR gilts (98 vs. 93%, P < 0.01) and more gilts developed on regimen AL than regimen Res (98 vs. 91%, P < 0.01) expressed estrus. Mean age at puberty was 178.6 d for LW/LR and 173.0 d for L45X gilts (P < 0.01) and 174.1 d for regimen AL and 177.5 d for regimen Res (P < 0.05). The Res regimen delayed pubertal development. Subsequently, it will be important to determine effects on reproduction through 4 parities.

Concentrations of gonadotropins, estradiol and progesterone in sows selected on an index of ovulation rate and embryo survival

The objective of this study was to determine concentrations of follicle stimulating hormone (FSH), luteinizing hormone (LH), progesterone (P4) and 17beta-estradiol (E2) in sows from a line selected on an index which emphasized ovulation rate (Select) and from a control line. A further classification of the sows in each line was made according to the estimated number of ovulations during an estrous cycle. Sows in the Select line were ranked into a high (HI) or low group (LI) when their estimated number of ovulations were 25 or more and 14 to 15, respectively. Sows of the control line were classified into groups as high (HC) or low (LC) when the estimated values for ovulation rate were 14-15 and 8-9 ovulations, respectively. Blood samples were collected every 12 h during a complete estrous cycle and samples were analyzed for concentrations of FSH and LH. Samples collected every 24 h were assayed for P4 and E2. Mean concentrations of FSH, LH, P4 and E2 did not differ (P > 0.10) between lines or between HI and LI or HC and LC groups. Selection of pigs for ovulation rate and embryonal survival did not affect concentrations of FSH, LH, P4 and E2 in sows during the estrous cycle.

Effects of social interactions on empirical responses to selection for average daily gain of boars

Effects of social interactions on responses to selection for ADG were examined with records of 9,720 boars from dam lines (1 and 2) and sire lines (3 and 4) provided by Pig Improvement Company. Each line was analyzed separately. Pens contained 15 boars. Average daily gains were measured from about 71 to 161 d of age and BW from 31 to 120 kg. Models included fixed effects of contemporary groups and initial test age as a covariate and random direct genetic (a), social genetic (c), social environmental (ce), and litter (lt) effects. Estimates of direct heritability with model 1 (the full model with a, c, ce, and lt) were 0.21, 0.28, 0.13, and 0.15 for lines 1 to 4. Estimates of heritability of social effects were near zero. Estimates of total heritable variance were 55, 52, 38, and 96% of phenotypic variance for lines 1 through 4. Empirical responses to selection with model 1 were calculated using the parameter estimates from model 1. For response of 1 genetic SD for both components (a and c), the proportions of expected total gain due to social effects (with economic weights of 1 and pen size-1 = 14) were 54, 28, 65, and 65% for the 4 lines. Genetic superiorities of the top 10% of boars were calculated for boars ranked using reduced models, but with EBV calculated using the full model (model 1). Average total breeding values (ETBV = EBV(a)+14EBV(c)) for the top 10% of boars selected with model 1 were 74.08, 94.26, 31.79, and 92.88 g for lines 1 through 4, respectively. For rankings based on model 2 (a, ce, and lt), but EBV calculated with model 1, average total breeding values for the top 10% were 68.15, 94.03, 7.33, and 84.72 g with empirical correlated responses for genetic social effects from selection for direct effects of 0.93, 1.89, -2.19, and 3.52 g for lines 1 to 4.

Selection for maternal behavior in mice—direct and correlated responses

Abstract Three generations of divergent selection for a maternal care index (MCI) in mice were practiced in each of three replicates. MCI was recorded for 29–32 dams and litters in each replicate/line subclass. Pups of the top (or bottom) 6–10 dams in each replicate, depending on number of females in the litters, were selected in high (H) and low (L) MCI lines. At birth, litters with more than 10 pups were standardized to 10 pups whereas litters with no more than 10 pups remained intact. On day 4, 8, 12, and 16 of lactation, time budgets during a 30-min session were recorded by real-time video camera. The times spent in the activities of nursing pups, licking pups, retrieving pups, resting with pups, and building a nest were summed, and MCI was the percentage of the total time devoted to these activities. Number born alive (NBA), number weaned (NW), litter weaning weight (LWW), and mating weight (MW) were recorded. The difference between H and L in cumulative selection differential (CSD) of MCI was 59.8%. Regressions of differences in H and L on generation and on cumulative selection differential were 4.878±0.414 and 0.239±0.011 (realized heritability), respectively ( P P