Genetic parameter estimation for number born alive at different parities in Landrace and Large White pigs

We estimated genetic parameters for number born alive (NBA) from the first to the seventh parities in Landrace and Large White pigs using three models. Analyzing 55,160 farrowing records for 12,677 Landrace dams and 43,839 for 10,405 Large White dams, we used a single‐trait animal model to estimate the heritability of NBA at each parity and a two‐trait animal model and a single‐trait random regression model to estimate the genetic correlations between parities. Heritability estimates of NBA at each parity ranged from 0.08 to 0.13 for Landrace and from 0.05 to 0.16 for Large White. Estimated genetic correlations between parities in all cases were positive. Genetic correlations between the first and second parities were slightly lower than those between other neighboring parities. Genetic correlations between more distant parities tended to be lower, in some cases <0.8. The results indicate the necessity to investigate the applicability of evaluating NBA at different parities as different traits (e.g., the first and later parities), although a repeatability model might still be reasonable.     

Comparison of two models to estimate genetic parameters for number of born alive in pigs

The performance of the two‐trait animal model that regards the first parity and later parities as two different traits in estimating genetic parameters for number of born alive (NBA) was examined using real and simulated data. Genetic parameters for NBA were estimated in purebred Landrace and Large White pigs using a single‐trait repeatability model (Model 1) that regards all parities as the same trait and a two‐trait animal model (Model 2) that regards the first and the later parities as different traits. For Model 2, the permanent environmental effect was fitted to only the records of the later parities. Heritability for NBA estimated using Model 1 was 0.12 for Landrace and 0.11 for Large White. Estimated heritability for NBA of the first parity and the later parities was 0.21 and 0.16, respectively, for Landrace; 0.18 and 0.16, respectively, for Large White obtained using Model 2, and higher than those in both breeds obtained using Model 1. Further results based on data simulated using the Monte Carlo method suggest that estimated additive genetic variance could be more biased using Model 2 than Model 1.     

妊娠期背膘厚对母猪产程及繁殖性能的影响

为优化母猪繁殖效率,探究妊娠期不同背膘厚对母猪繁殖性能和分娩产程的影响,本研究以广西某公司2 969头大白母猪和1 787头长白母猪为试验群体,收集2017年1月至2017年10月妊娠期3个阶段(妊娠30、80和107 d)背膘厚与分娩接产记录数据,分析背膘厚与分娩产程、总产仔数、产活仔数和初生窝重等性状的关系。研究结果表明,大白母猪分娩产程时间显著短于长白母猪(P<0.05),大白母猪总产仔数、产活仔数和初生窝重显著优于长白母猪(P<0.05)。在妊娠30 d时,背膘厚在18～20 mm组的大白母猪总产仔数和产活仔数最高,且初生窝重最大;背膘厚在18～20 mm组的长白母猪总产仔数和产活仔数最高。在妊娠80 d时,背膘厚≥20 mm组的大白母猪总产仔数和产活仔数最高,且初生窝重最大、产程最短;背膘厚在16～18 mm组的长白母猪总产仔数和产活仔数最高,且初生窝重较高、母猪产程较短。在妊娠107 d时,背膘厚在14～16 mm组的大白母猪总产仔数和产活仔数最高,且初生窝重最大,但母猪产程与其他组差异不显著(P>0.05);背膘厚≥20 mm组的长白母猪总产仔数和产活仔数最高,且初生窝重较大。妊娠期背膘厚减少1～2 mm的大白母猪,其总产仔数和产活仔数最高,初生窝重较小,产程较长。而背膘厚减少>2 mm的长白母猪,其总产仔数和产活仔数最高,初生窝重较大,产程较短。上述试验结果说明,在母猪妊娠期间,合适的背膘厚可有效提高母猪繁殖性能和母猪分娩期间的福利水平。养殖场可以根据营养配方和猪群品种建立背膘数据库,通过精准饲喂将母猪背膘厚调整至最佳范围,同时合理控制妊娠期背膘变化。     

Genetic relationship of litter traits between farrowing and weaning in Landrace and Large White pigs

We estimated genetic parameters in Landrace and Large White pig populations for litter traits at farrowing (total number born, number born alive, number stillborn, total litter weight at birth (LWB), and mean litter weight at birth) and those at weaning (litter size at weaning (LSW), total litter weight at weaning (LWW), mean litter weight at weaning (MWW), and survival rate from farrowing to weaning). We analyzed 65,579 records at farrowing and 6,306 at weaning for Landrace, and 52,557 and 5,360, respectively, for Large White. Single‐trait and two‐trait repeatability animal models were exploited to estimate heritability and genetic correlation respectively. Heritability estimates of LSW were 0.09 for Landrace and 0.08 for Large White. Genetic correlations of LSW with MWW were –0.43 for Landrace and –0.24 for Large White. Genetic correlations of LSW with LWW and LWB ranged from 0.5 to 0.6. The genetic correlation of MWW with LWW was positive, but that with LWB was negligible. The results indicate that utilizing LWW or LWB could improve LSW efficiently, despite the antagonistic genetic correlation between LSW and MWW.     

Genetic analysis of sow longevity and sow lifetime reproductive traits using censored data

Sow longevity is a key component for efficient and profitable pig farming; however, approximately 50% of sows are removed annually from a breeding herd. There is no consensus in the scientific literature regarding a definition for sow longevity; however, it has been suggested that it can be measured using several methods such as stayability and economic indicators such as lifetime piglets produced. Sow longevity can be improved by genetic selection; however, it is rarely included in genetic evaluations. One reason is elongated time intervals required to collect complete lifetime data. The effect of genetic parameter estimation software in handling incomplete data (censoring) and possible early indicator traits were evaluated analysing a 30% censored data set (12 725 pedigreed Landrace × Large White sows that included approximately 30% censored data) with DMU6, THRGIBBS1F90 and GIBBS2CEN. Heritability estimates were low for all the traits evaluated. The results show that the binary stayability traits benefited from being analysed with a threshold model compared to analysing with a linear model. Sires were ranked very similarly regardless if the program handled censoring when all available data were included. Accumulated born alive and stayability were good indicators for lifetime born alive traits. Number of piglets born alive within each parity could be used as an early indicator trait for sow longevity.     

Effect of leg conformation on survivability of Duroc, Landrace, and Large White sows

Sow longevity influences farm economy and can be considered an important indicator of animal welfare. Body features such as leg conformation can play a key role in sow longevity, although little is known about its effect on culling decisions. Within this context, longevity data from 587 Duroc, 239 Landrace, and 217 Large White sows were analyzed with special emphasis on the effect of leg conformation. Sow longevity was analyzed twice for each breed, testing the effect of a subjective overall score for leg conformation, or the presence or absence of 6 specific leg conformation defects. Each preliminary model also included a teat conformation score with 3 levels, farm or origin, backfat thickness at 6 mo of age, and 2 continuous sources of variation, namely the age at the first farrowing and the number of piglets born alive at each farrowing. Overall leg conformation score influenced (P < 0.01) sow longevity in Duroc, Landrace, and Large White sows, with a greater hazard ratio (HR) for poorly conformed sows (1.56, 2.16, and 1.79, respectively) than for well-conformed sows (0.32, 0.66, and 0.68, respectively). Abnormal hoof growth reduced survivability in Duroc (HR = 2.78; P < 0.001) and Landrace sows (HR = 1.88; P < 0.01); the presence of splayed feet (P < 0.05) or bumps and injuries (P < 0.001) increased the risk of culling in Duroc sows (HR = 2.08 and 3.57, respectively), whereas the incidence of straight pastern increased the HR in Large White sows (HR = 2.49; P < 0.01). In all 3 breeds, longevity decreased for plantigrade sows, with a greater HR in Duroc (HR = 3.38; P < 0.001) than in Landrace (HR = 1.53; P < 0.10) and Large White sows (HR = 1.73; P < 0.05). Teat conformation did not influence sow longevity (P > 0.10). Estimates of heritability for longevity in Duroc sows ranged from 0.05 to 0.07 depending on the algorithm applied. Leg conformation had a substantial effect on sow longevity, where an accurate removal of poorly leg-conformed candidate gilts before first mating could improve sow survival and reduce culling costs. These moderate estimates of heritability indicated that survivability of Duroc sows could be genetically improved by direct selection for leg conformation.     

胎次、产仔月份及纯繁/杂交对母猪产仔性能的影响

本研究统计分析了部分非遗传因素(胎次、产仔月份及纯繁/杂交)对长白、大白和杜洛克母猪产仔性能(总产仔数、产活仔数及初生窝重)的影响,旨在为后备母猪的选种提供指导。结果表明,2~5胎仔猪的初生窝重较重;其中2、3胎的初生窝重极显著高于头胎及6胎之后的仔猪初生窝重(P<0.01)。3月份总产仔数、产活仔数及初生窝重极显著高于其他月份(P<0.01),且11月份初生窝重显著低于其他月份(P<0.05)。长白纯繁母猪在产活仔数方面极显著优于大白纯繁母猪和长白×大白杂交母猪(P<0.01);在初生窝重方面,大白×长白杂交母猪的初生窝重极显著高于大白纯繁母猪和长白×大白杂交母猪(P<0.01)。第2胎与3~4胎、第3胎与第4胎的总产仔数呈极显著正相关(P<0.01)。综上所述,该猪场母猪3~6胎的产仔性能较好,且以1~4月份的产仔性能为佳;配种方式以长白纯繁和大白×长白杂交为宜;第2胎产仔性能可作为后备母猪选留的重要依据。     

Estimation of genetic parameters for farrowing traits in purebred Landrace and Large White pigs

Genetic parameters were estimated for six reproductive traits related to farrowing events in Landrace and Large White pigs; total number born (TNB), number born alive (NBA), number stillborn (NSB), total litter weight at birth (LWB), mean litter weight at birth (MWB), and gestation length (GL). We analyzed 62,534 farrowing records for 10,637 Landrace dams and 49,817 farrowing records for 8,649 Large White dams. Estimated heritabilities of TNB, NBA, NSB, LWB, MWB, and GL by single‐trait repeatability model analyses were 0.12, 0.12, 0.08, 0.18, 0.19, and 0.29, respectively, in Landrace, and 0.12, 0.10, 0.08, 0.18, 0.16, and 0.34, respectively, in Large White. Genetic correlation between NBA and NSB was unfavorable: 0.20 in Landrace and 0.33 in Large White. Genetic correlations of GL with the other five traits were weak: from ?0.18 with NSB to ?0.03 with NBA in Landrace, and from ?0.22 with NSB to ?0.07 with NBA in Large White. LWB had a highly favorable genetic correlation with NBA (0.74 in both breeds), indicating the possibility of using LWB for the genetic improvement of NBA.     

Identification of mutations of zona pellucida glycoprotein (ZP3) and its association with pig reproductive traits

Reproduction is a complex trait, controlled by genetic and environmental factors. Genetic improvement of this trait is important for animal breeders to improve the animal's production efficiency. Apart from genetic factors, animal production can be affected by environmental factors, i.e. the nursing ability of the sow, which is in turn affected directly by effective teat number (teats producing milk normally, TN) and number of piglets born alive (NBA). The objective of this study was to find new mutations, such as single nucleotide polymorphisms (SNPs) from the Zona Pellucida glycoprotein gene (ZP3) using Single Strand Chain Polymorphism (SSCP) and nucleotide sequencing and to investigate association between genetic variations and sow reproductive traits. We identified 13 new SNPs from exon 1, two new SNPs from intron 2, one SNP from intron 6 and a 18 bp (GCACGTGGTCCTCCTGG)‐deletion/insertion from intron 2 of the ZP3 gene. Five out of these mutations were selected to genotype in five different breeds (Small Meishan, Qingping, Duroc, Landrace and Large White) and association with reproductive traits in European breeds (Duroc, Landrace and Large White). The sows with genotype AA had more 1.11 piglets NBA than of the sows with genotype AB (p < 0.05) in the 18 bp deletion/insertion of intron 2, while non‐significant associations between the other mutations and reproductive traits (NBA and TN) were found.     

Genetic associations of prolificacy with performance, carcass, meat quality, and leg conformation traits in the Finnish Landrace and Large White pig populations

The objective of this study was to estimate genetic associations of prolificacy traits with other traits under selection in the Finnish Landrace and Large White populations. The prolificacy traits evaluated were total number of piglets born, number of stillborn piglets, piglet mortality during suckling, age at first farrowing, and first farrowing interval. Genetic correlations were estimated with two performance traits (ADG and feed:gain ratio), with two carcass traits (lean percent and fat percent), with four meat quality traits (pH and L* values in longissimus dorsi and semimembranosus muscles), and with two leg conformation traits (overall leg action and buck-kneed forelegs). The data contained prolificacy information on 12,525 and 10,511 sows in the Finnish litter recording scheme and station testing records on 10,372 and 9,838 pigs in Landrace and Large White breeds, respectively. The genetic correlations were estimated by the restricted maximum likelihood method. The most substantial correlations were found between age at first farrowing and lean percent (0.19 in Landrace and 0.27 in Large White), and fat percent (-0.26 in Landrace and -0.18 in Large White), and between number of stillborn piglets and ADG (-0.38 in Landrace and -0.25 in Large White) and feed:gain (0.27 in Landrace and 0.12 in Large White). The correlations are indicative of the benefits of superior growth for piglets already at birth. Similarly, the correlations indicate that age at first farrowing is increasing owing to selection for carcass lean content. There was also clear favorable correlation between performance traits and piglet mortality from birth to weaning in Large White (r(g) was -0.43 between piglet mortality and ADG, and 0.42 between piglet mortality and feed:gain), but not in Landrace (corresponding correlations were 0.26 and -0.22). There was a general tendency that prolificacy traits were favorably correlated with performance traits, and unfavorably with carcass lean and fat percents, whereas there were no clear associations between prolificacy and meat quality or leg conformation. In conclusion, accuracy of estimated breeding values may be improved by accounting for genetic associations between prolificacy, carcass, and performance traits in a multitrait analysis.     

Impact of dominance effects on sow longevity

The purpose of the current study was to estimate variance components, especially dominance genetic variation, for overall leg action, length of productive life and sow stayability until third and fifth parity in the Finnish pig populations. The variance components were estimated in two purebred [Landrace (LR), n = 23 602 and Large White (LW), n =22 984] and crossbred (LR × LW, n = 17 440) data sets. Five different analyses were carried out for all the traits to compare the effect of sows’ inbreeding, common litter environment and parental dominance in the statistical model when determining the genetic correlations of the traits for the two purebred and crossbred populations. Estimated heritabilities for the traits ranged from 0.04 to 0.06. The estimates for the proportion of dominance variance of phenotypic variance (d²) varied between 0.01 and 0.17, and was highest in the crossbred dataset. The genetic correlations of the same traits in purebred and crossbred were all high (>0.75). Based on current results, the effect of dominance should be accounted for in the breeding value estimation of sow longevity, especially when data from crossbred animals are included in the analyses. Because dominance genetic variation for sow longevity exists that variation should be utilized through planned matings in producing sows for commercial production.     

Phenotypic and genetic variation in longevity of Polish Landrace sows

The influence of some production traits on the longevity of Polish Landrace sows was evaluated using survival analysis. Estimates of genetic parameters were obtained from the sire and animal components in linear and survival methodologies. Comparison between survival and linear models was based on heritabilities and ranking of estimated breeding values of sires. The same data set, 13 031 sows, was used for both methodologies, even in the presence of censored observations. The effects of herd*year and year*season of the first farrowing had the largest influence on the risk of culling of sows. Sows born in spring season (March–May) had a 24% (p < 0.001) lower hazard for removal than those born in winter (December–February). The age at first farrowing had a small but significant effect on culling: the hazard regression coefficient for this trait was 0.002 per day. Sows that had more piglets born alive and fewer stillborn in the first litter had a decreased risk of being culled. Within a contemporary group, slower growing gilts had decreased removal risk. The relative risk ratios show a marginal decreased rate of culling for sows with backfat thickness between 9.5 and 11 mm compared to the leaner sows. Loin depth had no effect on sow longevity. Heritability estimates ranged from 0.09 to 0.38 depending on the model and type of analysis. In survival analysis, all heritabilities for longevity were higher when analysed with sire models (0.21 and 0.38) compared to animal models (0.09 and 0.16). The use of animal or sire models in the linear analysis gave similar heritability estimates (0.12 and 0.10). Correlations between breeding values for sires were moderate and high, with absolute values from 0.51 to 0.99, depending on the model fitted and methodology. A stronger correlations within methodologies (0.83–0.99) than within models with different methodologies (0.51–0.63) were obtained.     

Genetics of length of productive life and lifetime prolificacy in the Finnish Landrace and Large White pig populations

The objective of this study was to estimate direct and indirect selection potential for length of productive life and lifetime prolificacy in Finnish Large White and Landrace swine populations. To study the direct selection potential, the heritabilities of these traits were estimated. The genetic correlations of length of productive life and lifetime prolificacy with prolificacy traits and overall leg conformation were estimated to evaluate whether selection for these traits could indirectly improve measures of sow longevity. In addition, correlations between length of productive life, lifetime prolificacy, ADG, and backfat thickness were estimated. Records were used from Finnish purebred Landrace (n = 26,744) and Large White (n = 24,007) sows born on operations that perform on-farm production tests on all females. Heritabilities were estimated using both a survival analysis procedure and a linear model. Due to computational limitations, correlations were estimated with the linear model only. Estimated length of productive life heritabilities obtained from linear model analyses were less (0.05 to 0.10) than those obtained from survival analyses (0.16 to 0.19). This may be indicative of the superiority of survival analysis compared with linear model analysis methods when evaluating longevity or similar types of data. All the prolificacy traits were genetically correlated with length of productive life and lifetime prolificacy, and the correlations were greater than 0.13. These results indicate that selection for increased number of piglets weaned in the first litter and for short first farrowing interval is beneficial for sow longevity and also for sow's lifetime prolificacy. The genetic correlations between length of productive life and leg conformation score also were favorable (0.32 in Landrace and 0.17 in Large White). The heritability estimates indicate that survival analysis is likely the most appropriate method of evaluating longevity traits in swine. Because of computational problems, simultaneous analysis of linear traits and longevity is not currently possible. More research is needed to develop methods for multiple linear and survival trait analyses.     

Between-breed variability of stillbirth and its relationship with sow and piglet characteristics

Litter characteristics at birth were recorded in 4 genetic types of sows with differing maternal abilities. Eighty-two litters from F(1) Duroc x Large White sows, 651 litters from Large White sows, 63 litters from Meishan sows, and 173 litters from Laconie sows were considered. Statistical models included random effects of sow, litter, or both; fixed effects of sow genetic type, parity, birth assistance, and piglet sex, as well as gestation length, farrowing duration, piglet birth weight, and litter size as linear covariates. The quadratic components of the last 2 factors were also considered. For statistical analyses, GLM were first considered, assuming a binomial distribution of stillbirth. Hierarchical models were also fitted to the data to take into account correlations among piglets from the same litter. Model selection was performed based on deviance and deviance information criterion. Finally, standard and robust generalized estimating equations (GEE) procedures were applied to quantify the importance of each effect on a piglet's probability of stillbirth. The 5 most important factors involved were, in decreasing order (contribution of each effect to variance reduction): difference between piglet birth weight and the litter mean (2.36%), individual birth weight (2.25%), piglet sex (1.01%), farrowing duration (0.99%), and sow genetic type (0.94%). Probability of stillbirth was greater for lighter piglets, for male piglets, and for piglets from small or very large litters. Probability of stillbirth increased with sow parity number and with farrowing duration. Piglets born from Meishan sows had a lower risk of stillbirth (P < 0.0001) and were little affected by the sources of variation mentioned above compared with the 3 other sow genetic types. Standard and robust GEE approaches gave similar results despite some disequilibrium in the data set structure highlighted with the robust GEE approach.     

Selection potential of different prolificacy traits in the finnish landrace and large white populations

Heritabilities and genetic correlations for different prolificacy traits were estimated to assess possibilities of selection for high number of piglets weaned. Three litter-size traits: total number of piglets born (TNB), number of piglets born alive (NBA), number of piglets weaned (NW); four piglet survival traits: number of stillborn piglets (NSB), percent of stillborn piglets (NSB%), piglet mortality between birth and weaning (PM), percent of dead piglets during suckling (PM%); and three traits measuring time intervals: age at first farrowing (AFF), first farrowing interval (FFI), and gestation length (GL) were analysed. The Finnish national litter recording scheme provided data on the first parity litters of 11 329 Landrace and 8 362 Large White pigs born between 1986 and 2000. The heritabilitiy estimates were moderate for AFF and GL (0.24–0.37), and low for all the other traits (0.03–0.11). The genetic correlations between TNB and PM (0.68 in Landrace and 0.43 in Large White) and between NBA and PM (0.64 in Landrace and 0.31 in Large White) suggest that selection only for high TNB or NBA will lead to increased PM. The results showed further that GL will increase indirectly if the selection pressure is for low PM (r _g =?0.050 in Landrace and ?0.43 in Large White.     

An assessment of reproductive and lifetime performances of Kagoshima Berkshire gilts and sows

We investigated the reproductive and lifetime performances of Kagoshima Berkshire gilts and sows. We examined 20 605 parity records of 4419 pigs for 2008 to 2012 on a farrow‐to‐finish commercial farm. The mean parity (± SD) of all animals was 3.0 ± 2.1. For farrowing performance, the highest numbers of total pigs born and pigs born alive were found in sows with parities 5 and 6 and with parity 3–6, respectively (P < 0.05). Regarding weaning and mating performance, sows with parity 2 had the lowest preweaning mortality (P < 0.05). The longest weaning‐to‐first‐mating interval was found in parity 1 pigs, and the interval decreased as parity increased (P < 0.05). Parities 0 and 1 pigs had the lowest farrowing rate and those with parity 4 had the highest farrowing rate (P < 0.05). The mean parity at culling, total number of pigs born alive in a lifetime, and nonproductive days in a lifetime were 5.5 ± 2.93, 49.2 ± 24.72 pigs, and 132.1 ± 83.34 days, respectively. These animals had a lower litter size and fertility that the F₁ crossbred sows mainly used in Japan, but a similar tendency for performance by parity.     

Dppa5基因遗传多态性及其与母猪繁殖性状的关联分析

试验旨在研究猪多潜能性维持因子5(developmental piuripotency associated 5,Dppa5)基因的遗传多态性及其与母猪繁殖性状的遗传效应。以长白猪和大白猪为试验群体,采用PCR-RFLP、克隆测序等方法分析检测猪Dppa5基因的多态性并对其与母猪产仔性能进行关联分析。结果表明,猪Dppa5基因外显子上存在2个错义突变位点:g.363 T> C和g.844 G> T;猪Dppa5基因g.363 T> C 位点对初产大白猪的总产仔数有极显著影响(P< 0.01),对经产大白猪、长白猪的产活仔数有显著影响(P< 0.05);g.844 G> T位点对经产长白猪和大白猪的总产仔数有显著影响(P< 0.05)。综合结果分析,Dppa5多态位点对猪的繁殖性能存在影响,可作为潜在的遗传标记,为猪的分子育种提供参考。     

Genetic Polymorphism of Dppa5 Gene and its Association with Reproductive Performance in Sow

The purpose of this study was to detect the genetic variation of the porcine developmental piuripotency associated 5 (Dppa5) gene and its association with reproductive performance in sow.PCR-RFLP and sequencing methods were used to detect SNPs and analyze its association with reproductive performance in Large White and Landrace sows.The results showed that two missense mutations g.363 T> C and g.844 G> T were detectd in exon of porcine Dppa5.SNP g.363 T> C affected total number born highly significantly in primiparous Large White sow (P< 0.01) and affected litter size and number born alive significantly in Large White and Landrace sows (P< 0.05).SNP g.844 G> T showed a significant impact on total number born in multiparous Landrace and Large White sows (P< 0.05).The results suggested that the SNPs of Dppa5 gene impacted reproductive performance of sows and could be genetic markers.     

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.