Estimation of the effects of selection on French Large White sow and piglet performance during the suckling period.

The effects of 21 yr of selection were estimated for sow and piglet performance during the suckling period in a French Large White (LW) pig population using frozen semen. Two experimental groups (EXP = L77 and L98) were produced by inseminating LW sows with either stored frozen semen from 17 LW boars born in 1977 (EXP = L77) or with fresh semen from 23 LW boars born in 1998 (EXP = L98). Seventy-four L77 and 89 L98 randomly chosen females were mated to 15 L77 and 15 L98, respectively, randomly chosen boars for 6 successive parities. They produced 2,796 L77 progeny (G77) and 3,529 L98 progeny (G98) piglets including stillbirths. To disentangle direct and maternal effects on piglet growth, a 2 × 2 factorial design was set by cross-fostering half-litters across genetic groups the day after farrowing, resulting in mixed G77/G98 litters nursed by either L77 or L98 sows. Piglet traits investigated included individual weight at birth (IWB), at 21 d of age (IW21d), and at weaning at 4 wk of age (IWW) and ADG from birth to 21 d of age (ADG21d) and from birth to weaning (ADGBW) as well as probability of stillbirth, probability of mortality on the first day after farrowing and from d 2 to weaning. Sow traits analyzed included weight before farrowing and at weaning, feed intake, milk production, colostrum, and milk composition. The variability of performance across genetic groups and litters was also investigated. The data were analyzed using generalized (piglet mortality) or linear mixed models (other traits). Results showed an increase in IWB (+240 ± 72 g in 21 yr for IWB adjusted for total number born), and a negative maternal genetic trend was observed on piglet growth during the suckling period (e.g., +33 ± 13 g/d in 21 yr for ADG21d, that is, 14% of the mean), whereas direct genetic effects remained unchanged. Piglets from L98 litters also had a 40% larger probability of being stillborn and a 28% larger probability of dying on d 1 and had a more heterogeneous IWB (358 vs. 336 g; < 0.001) and growth during the suckling period (60 vs. 56 g/d; < 0.001). Sows from L77 and L98 experimental groups did not differ in weight, feed intake, colostrum, and milk composition. These results give evidence of negative correlated effects of selection for piglet traits related to robustness. These adverse effects are at least partly of maternal origin.

Estimation of the effects of selection on French Large White reproductive performance using frozen semen.

Genetic trends for male and female sexual development and components of litter size and weight at birth (LB) as well as traits related to sow lifetime productivity were estimated in a French Large White (LW) pig population using frozen semen. Two experimental groups (EXP = L77 and L98) were produced by inseminating LW sows with either stored frozen semen from 17 LW boars born in 1977 (EXP = L77) or with semen from 23 LW boars born in 1998 (EXP = L98). In each group, about 100 males were measured for testicular development and bulbo-urethral gland development, and 90 gilts were checked for puberty, among which about 50 gilts were measured for their first ovulation rate at puberty (ORP). The females were then mated to 15 randomly chosen males for each group for 6 successive parities and measured for total number born (TNB), number born alive (NBA), litter weight at birth (LWB), and interval from weaning to first estrus as well as ovulation rate at fertilization (ORF = ovulation rate of gestating sows) on a subset of litters. The data were analyzed using mixed linear models including the fixed effects of EXP, of finishing (sexual development traits) or farrowing group, and parity (LB traits); the random effects of birth litter (sexual development traits) or sow (LB traits); and, when relevant, age or BW as covariates. The homogeneity of residual variances across EXP was also tested. For each trait, the genetic trend was estimated as twice the difference between L98 and L77. Limited differences were observed for sexual development traits, except for ORF, which increased by 0.17 ± 0.06/yr. The residual SD of NBA (2.7 vs. 2.0; = 0.004) and LWB (3.1 vs. 2.5; = 0.03) were larger in L98 sows than in L77 sows. Positive trends were observed for all litter traits (0.22 ± 0.07 ova, 0.12 ± 0.04 piglet, 0.09 ± 0.04 piglet, and 0.23 ± 0.06 kg/yr for ORF, TNB, NBA, and LWB, respectively) but at the expense of a degradation of prenatal and farrowing survival. A negative trend was also observed for length of productive life (-8.9 ± 3.9 d/yr). These results suggest that gains in productivity were associated with a loss of robustness.

Estimation of genetic trends from 1977 to 2000 for stress-responsive systems in French Large White and Landrace pig populations using frozen semen.

An experimental design aiming at analysing the consequences of genetic selection from 1977 to 1998-2000 on the evolution of stress-responsive systems in the French Large White (LW) and Landrace (LR) pig populations was conducted by INRA and IFIP-Institut du Porc. Large White sows were inseminated with semen from LW boars born in 1977 (frozen semen) or in 1998 and their second-generation offspring were station-tested. Landrace sows were inseminated with semen from LR boars born in 1977 (frozen semen) or in 1999 to 2000, and their progeny was station-tested. Urinary concentration of stress hormones (cortisol and catecholamines) and traits related to carcass composition (estimated carcass lean content (ECLC) and global adiposity) and meat quality (pH 24 h) were measured. For the two populations, selection carried out since 1977 led to an increase in ECLC and a decrease in carcass adiposity. Between 1977 and 1998 to 2000, urinary concentrations of stress hormones were unchanged in the LR breed, but were decreased in the LW breed. Moreover, for the animals generated from LW boars born in 1977 and in 1998, urinary cortisol levels were negatively correlated with ECLC. Therefore, in the LW breed, selection carried out for higher ECLC resulted in a decrease in cortisol production, as well as a reduction of catecholamine production that may be responsible for the lower ultimate pH of meat. Therefore, selection carried out for increased carcass lean content led, in this breed, to large modifications in the functioning of the stress-responsive systems, thereby influencing a large range of physiological regulations and technical properties such as carcass composition and meat pH, which remained however in the normal range for acceptable meat quality.

Correlated responses of pre- and postweaning growth and backfat thickness to six generations of selection for ovulation rate or prenatal survival in French Large White pigs.

Correlated effects of selection for components of litter size on growth and backfat thickness were estimated using data from 3 pig lines derived from the same base population of Large White. Two lines were selected for 6 generations on either high ovulation rate at puberty (OR) or high prenatal survival corrected for ovulation rate in the first 2 parities (PS). The third line was an unselected control (C). Genetic parameters for individual piglet BW at birth (IWB); at 3 wk of age (IW3W); and at weaning (IWW); ADG from birth to weaning (ADGBW), from weaning to 10 wk of age (ADGPW), and from 25 to 90 kg of BW (ADGT); and age (AGET) and average backfat thickness (ABT) at 90 kg of BW were estimated using REML methodology applied to a multivariate animal model. In addition to fixed effects, the model included the common environment of birth litter, as well as direct and maternal additive genetic effects as random effects. Genetic trends were estimated by computing differences between OR or PS and C lines at each generation using both least squares (LS) and mixed model (MM) methodology. Average genetic trends for direct and maternal effects were computed by regressing line differences on generation number. Estimates of direct and maternal heritabilities were, respectively, 0.10, 0.12, 0.20, 0.24, and 0.41, and 0.17, 0.33, 0.32, 0.41, and 0.21 (SE = 0.03 to 0.04) for IWB, IW3W, IWW, ADGBW, and ADGPW. Genetic correlations between direct and maternal effects were moderately negative for IWB (-0.21 +/- 0.18), but larger for the 4 other traits (-0.59 to -0.74). Maternal effects were nonsignificant and were removed from the final analyses of ADGT, AGET, and ABT. Direct heritability estimates were 0.34, 0.46, and 0.21 (SE = 0.03 to 0.05) for ADGT, AGET, and ABT, respectively. Direct and maternal genetic correlations of OR with performance traits were nonsignificant, with the exception of maternal correlations with IWB (-0.28 +/- 0.13) and ADGPW (0.23 +/- 0.11) and direct correlation with AGET (-0.23 +/- 0.09). Prenatal survival also had low direct but moderate to strong maternal genetic correlations (-0.34 to -0.65) with performance traits. The only significant genetic trends were a negative maternal trend for IBW in the OR line and favorable direct trends for postweaning growth (ADGT and AGET) in both lines. Selection for components of litter size has limited effects on growth and backfat thickness, although it slightly reduces birth weight and improves postweaning growth.

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.

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).

Estimation of genetic trends from 1977 to 1998 for farrowing characteristics in the French Large White breed using frozen semen.

The objective of the study was to estimate genetic trends from 1977 to 1998 in the French Large White (LW) breed for stillbirth and associated traits measured at farrowing using frozen semen. Two groups of pigs (G77 and G98) were obtained by inseminating LW sows with semen from LW boars born either in 1977 or in 1998. A second generation was produced by inter se mating in each group. Farrowing was thoroughly supervised through both direct observations and video recording all long farrowing on a total of 137 first- and second-parity litters produced by sows from this second generation (68 G77 and 69 G98 litters, respectively). Measurements included birth time, weight and birth characteristics (including orientation, presence of cyanosis or oedema, membrane obstruction, umbilical cord length/content) of each piglet, as well as sow traits (weight and backfat thickness, farrowing duration, litter size and within-litter variation of weights at birth). The data were analysed using linear or generalised linear mixed models, according to the definition of the trait (continuous or binary data). The importance of several effects to piglet probability of stillbirth was then quantified by computing the reduction of variance associated with the addition of each effect in the model. Litter size did not significantly differ in first parity, but was higher in G98 second-parity sows: the differences for global (including pre partum dead piglets) and total numbers of piglets born per litter were +2.3 ± 1.1 and +1.3 ± 0.6, respectively. G98 sows also had a higher number of stillbirths in both parities (+0.7 ± 0.3 stillborn per litter). Piglets from G98 litters were heavier at birth (+130 ± 40 g for birth weight adjusted for litter size), without any increase in within-litter heterogeneity of birth weight. No significant difference was detected between G77 and G88 groups for farrowing length and the distribution of time interval between piglet births. G98 stillborn piglets had longer and more often empty umbilical cords at birth. G98 piglets born alive also had more often umbilical nodes than G77 piglets. These characteristics were considered as indicators of increased farrowing difficulties and risk of hypoxia at birth in G98 pigs. Time of birth of each piglet, sow fatness at farrowing and time of first placenta expulsion were the main factors of variation of the piglet's probability of stillbirth.

Estimation of genetic trends from 1977 to 1998 of body composition and physiological state of Large White pigs at birth.

Genetic trends for body composition and blood plasma parameters of newborn piglets were estimated through the comparison of two groups of pigs (G77 and G98, respectively) produced by inseminating Large White (LW) sows with semen from LW boars born either in 1977 or in 1998. Random samples of 18 G77 and 19 G98 newborn piglets were used for whole carcass and tissue sampling. Plasma concentrations of glucose, albumin and IGF-1 were determined on 75 G77 and 90 G98 piglets from 18 litters. The G98 piglets had less carcass dry matter, protein and energy (P < 0.01) than their G77 counterparts. When expressed in g/kg birth weight, livers were lighter (P < 0.001) and contained less glycogen (P < 0.01) in G98 piglets, with no difference in the activity of the hepatic glucose-6-phosphatase between G98 and G77 piglets. Concentrations of protein, DNA, RNA in longissimus dorsi muscle were unaffected by selection. Plasma concentrations of glucose (P < 0.05) and IGF-1 (P < 0.01) were lower in G98 than in G77 piglets. On the whole, the results suggest that the improvement in lean growth rate and in sow prolificacy from 1977 to 1998 has resulted in a lower maturity of piglets at birth.

Effects of quantitative trait loci on chromosomes 1, 2, 4, and 7 on growth, carcass, and meat quality traits in backcross Meishan x Large White pigs.

The aim of this work was to estimate whether genetic dissection of QTL on chromosomes 1, 2, 4, and 7, detected in an F2 Meishan x Large White population, can be achieved with a recombinant back-cross progeny test approach. For this purpose, a first generation of backcross (BC1) was produced by using frozen semen of F1 Large White x Meishan boars with Large White females. Four BC1 boars were selected because of their heterozygosity for at least 1 of the 4 regions. The BC1 boars were crossed with Large White sows, and the resulting BC2 offspring were measured for several growth and body composition traits. Contrary to the F2 animals, BC2 animals were also measured for meat quality traits in adductor, gluteus superficialis (GS), longissimus dorsi, and biceps femoris (BF) muscles. Each BC1 boar was tested for a total of 39 traits and for the 4 regions with statistical interval mapping analyses. The QTL effects obtained in BC1 families showed some differences compared with those described in F1 families. However, we confirmed QTL effects for growth in the SW1301-SW2512 markers interval on chromosome 1 and also for body composition in the SW1828-SW2512 markers interval on chromosome 1, in the SW2443-SWR783 markers interval on chromosome 2, and in the SW1369-SW632 markers interval on chromosome 7. In addition, we detected new QTL for growth traits on chromosome 2 and for meat quality traits on chromosomes 1 and 2. Growth of animals from weaning to the end of the test was influenced by the IGF2 gene region on chromosome 2. Concerning meat quality, ultimate pH of adductor, longissimus dorsi, and BF were affected by the interval delimited by UMNP3000 and SW2512 markers on chromosome 1, and a* of GS, L* of BF, and water-holding capacity of GS were affected by QTL located between marker loci SW2443 and SWR783 on chromosome 2. Recombinant progeny testing appeared to be a suitable strategy for the genetic dissection of the QTL investigated.

Exclusion of the swine leukocyte antigens as candidate region and reduction of the position interval for the Sus scrofa chromosome 7 QTL affecting growth and fatness.

Pig chromosome 7 (SSC 7) has been shown to be rich in QTL affecting performance and quality traits. Most studies mapped the QTL close to the swine leukocyte antigens (SLA), which has a large effect on adaptability and natural selection. Previous comparative mapping studies suggested that the 15-cM region limited by markers LRA1 (mapped at 55 cM) and S0102 (mapped at 70 cM) contains hundreds of genes. To decrease the number of candidate genes, we improved the mapping resolution with a genetic chromosome dissection through a backcross recombinant progeny test program between Meishan (MS) and European (EU; i.e., Large White or Landrace) breeds. Three first-generation backcross--(EU x MS) x EU--and two second-generation backcross--([EU x MS] x EU) x EU--sires carrying a recombination in the QTL mapping interval were progeny-tested (i.e., measured for a total of 44 growth, fatness, carcass and meat quality traits). Progeny family size varied from 29 to 119 pigs. Animals were genotyped for markers covering the region of interest. Progeny-test results allowed the QTL interval to be decreased from 15 to 20 cM down to 10 cM, and even less than 6 cM if we assumed that the EU pigs used in this study share only one QTL allele. Except for a putative QTL affecting some carcass composition traits, the SLA is excluded as a candidate region, suggesting that it might be possible to apply a marker-assisted selection strategy for this QTL, while controlling SLA allele diversity. The strong QTL effects remaining in animals with only 12.5% (issued from first-generation backcross boars) and 6.25% (issued from second-generation back-cross boars) Meishan genetic background shows that epistatic interactions are likely to be limited. Finally, the QTL does not have strong effects on meat quality traits.

Phenotypic and genetic parameters for longissimus muscle fiber characteristics in relation to growth, carcass, and meat quality traits in large white pigs.

A total of 383 barrows and gilts from a French Large White experimental herd were slaughtered at 100 kg BW. Samples of longissimus muscle were taken to categorize myofibers according to their contractile (I, IIA, and IIB) and metabolic (oxidative and nonoxidative) properties. Myofiber percentages, cross-sectional areas (CSA), and relative areas were measured. Growth rate, carcass composition, muscle chemical composition, metabolic enzyme activities, and meat quality traits were also measured to estimate phenotypic and genetic correlations between these traits and myofiber characteristics. Genetic parameters were estimated using a REML procedure applied to an individual animal model. Heritabilities of fiber traits were moderate to high (h2 = .20 to .59). Highest heritabilities were found for type I fiber percentage (h2 = .46 +/- .11), type IIBw fiber percentage (h2 = .58 +/- .11), and type I fiber cross-sectional area (h2 = .59 +/- .10). For a given fiber type, the relative area was phenotypically and genetically more closely related to the percentage than to the CSA. Phenotypic correlations between fiber type composition and other traits were low. Genetically, growth rate, carcass leanness, and loin eye area were positively related to fiber CSA. Intramuscular fat content was not related to fiber type composition (r(g) = -.05 to .06), whereas it was positively related to fiber CSA (r(g) = .68). Type IIBw fiber percentage was related to pH at 30 min (r(g) = -.46), pH at 24 h (r(g) = -.62), glycolytic potential (r(g) = .31), and lightness of color (r(g) = .55) of longissimus muscle.

Genetic resistance of Guadeloupe native goats to heartwater.

The resistance rate of different populations of the same breed of creole Guadeloupean goats to Cowdria ruminantium infection varied greatly depending on the previous heartwater history of each population. After experimental infection of goats removed decades ago from endemic areas, the observed resistance rate was 25%, while it was 54% in a population that had been isolated from the disease for 10 years and reached 78% in a flock actually exposed to heartwater. This resistance seems to be under genetic control as sex and paternity were the most important factors which could explain resistance in a group of 90 kids of the same flock, tested under controlled conditions. Resistance rate varied greatly (20-83%) depending on the sire, with a heritability estimate of 0.49 for half sibs and 0.85 for full sibs. A recessive sex-linked gene could be involved in the genetic determination of this resistance. From these observations, it can be stated that in endemic heartwater areas, each population, i.e. each flock, will have developed resistance at a definite rate according to population, age and the extent of past and present exposure to the disease, through a natural selection of resistant lines. Populations removed from exposure to heartwater will progressively lose their ability to resist infection through an increase in the frequency of susceptible stock. If our hypothesis of a recessive sex-linked gene is proved correct, it should be easy to select for improved resistance to the Guadeloupe breed of goat to heartwater.