Genome-wide associations for immune traits in two maternal pig lines.

BACKGROUND: In recent years, animal welfare and health has become more and more important in pig breeding. So far, numerous parameters have been considered as important biomarkers, especially in the immune reaction and inflammation. Previous studies have shown moderate to high heritabilities in most of these traits. However, the genetic background of health and robustness of pigs needs to be extensively clarified. The objective of this study was to identify genomic regions with a biological relevance for the immunocompetence of piglets. Genome-wide Association Studies (GWAS) in 535 Landrace (LR) and 461 Large White (LW) piglets were performed, investigating 20 immune relevant traits. Besides the health indicators of the complete and differential blood count, eight different cytokines and haptoglobin were recorded in all piglets and their biological dams to capture mediating processes and acute phase reactions. Additionally, all animals were genotyped using the Illumina PorcineSNP60v2 BeadChip. RESULTS: In summary, GWAS detected 25 genome-wide and 452 chromosome-wide significant SNPs associated with 17 immune relevant traits in the two maternal pig lines LR and LW. Only small differences were observed considering the maternal immune records as covariate within the statistical model. Furthermore, the study identified across- and within-breed differences as well as relevant candidate genes. In LR more significant associations and related candidate genes were detected, compared with LW. The results detected in LR and LW are partly in accordance with previously identified quantitative trait loci (QTL) regions. In addition, promising novel genomic regions were identified which might be of interest for further detailed analysis. Especially putative pleiotropic regions on SSC5, SSC12, SSC15, SSC16 and SSC17 are of major interest with regard to the interacting structure of the immune system. The comparison with already identified QTL gives indications on interactions with traits affecting piglet survival and also production traits. CONCLUSION: In conclusion, results suggest a polygenic and breed-specific background of immune relevant traits. The current study provides knowledge about regions with biological relevance for health and immune traits. Identified markers and putative pleiotropic regions provide first indications in the context of balancing a breeding-based modification of the porcine immune system.

Suitability of traits related to aggression and handleability for integration into pig breeding programmes: Genetic parameters and comparison between Gaussian and binary trait specifications.

Changes in husbandry systems as well as consumers' increasing demands for animal welfare lead to increasing importance of traits such as handleability and aggressiveness in pigs. However, before using such novel traits for selection decisions, information on genetic parameters for these traits for the specific population is required. Therefore, weight gain and behaviour-related traits were recorded in 1004 pigs (814 Pietrain x German Landrace crossbred, 190 German Landrace purebred) at different ages. Behaviour indicators and tests were assessed and conducted, respectively under commercial farm conditions and included scoring of skin lesions (twice) and behaviour during backtests (twice), injections (once), handling (twice) and weighing (three times). Since behaviour scores often exhibit suboptimal statistical properties for parametric analyses, variance components were estimated using an animal model assuming a normal (Gaussian, GA; all traits) and additionally a binary distribution of variables (BI; using a logit-link function for all behaviour traits). Heritabilities for behavioural traits ranged from 0.02 ± 0.04 (finishing pig handling test; BI) to 0.36 ± 0.08 (backtest 2; GA) suggesting that some of the traits are potentially useful for genetic selection (e.g. finishing pig weighing test: h2 (GA) = 0.20 ± 0.07). Only minor differences were observed for results from binary and Gaussian analyses of the same traits suggesting that either approach might yield valid results. However, four-fold cross-validation using correlations between breeding values of a sub-set of animals for the sample trait finishing pig weighing score indicated slight superiority of the logit model (r = 0.85 ± 0.04 vs. r = 0.77 ± 0.03). Generally, only weak to moderate associations were found between behavioural reactions to the same test at different ages (rp ≤ 0.11 for weighing at different ages; rp = 0.30 but rg (GA) = 0.84 ± 0.11 for the backtests) as well as between reactions to different tests. Therefore, for inclusion of behaviour traits into breeding programmes, and considering high labour input required for some tests such as the backtest, it is recommended to assess behaviour during situations that are relevant and identical to practical conditions, while the use of indicator traits generally does not appear to be a very promising alternative.

Variance components of aggressive behavior in genetically highly connected Pietrain populations kept under two different housing conditions.

Mixing of unfamiliar pigs is a standard management procedure in commercial pig production and is often associated with a period of intense and physically damaging aggression. Aggression is considered a problem for animal welfare and production. The objective of the present paper was to investigate the genetic background of aggressive behavior traits at mixing of unfamiliar gilts under 2 different housing conditions. Therefore, a total of 543 purebred Pietrain gilts, from 2 nucleus farms (farm A: n = 302; farm B: n = 241) of 1 breeding company, were tested at an average age of 214 d (SD 12.2 d) for aggressive behavior by 1 observer. Observations included the frequencies of aggressive attack and reciprocal fighting during mixing with unfamiliar gilts. On farm A 41% of the gilts were purebred Pietrains, whereas 59% were purebred Landrace or Duroc gilts. On the farm B 42% of the gilts were purebred Pietrains, and 58% purebred Large White gilts. The average size of the newly mixed groups of gilts was 28 animals on farm A and 18 animals on farm B. The Pietrain gilts from the 2 herds were genetically closely linked. They were the offspring of 96 sires, with 64% of these sires having tested progeny in both farms. There were clear differences in the housing of the animals between the 2 farms. The test pen on farm A had a solid concrete floor littered with wooden shavings and was equipped with a dry feeder. On farm B there was a partly slatted floor, and the gilts were fed by an electronic sow feeder. Mean space allowance was 2.6 m(2)/gilt on farm A and 3.9 m(2)/gilt on farm B. Although large interindividual differences existed, gilts from farm B performed numerically more aggressive attack (mean 1.12, SD 1.42 vs. mean 0.71, SD 1.20) and reciprocal fighting (mean 0.78, SD 0.98 vs. mean 0.44, SD 0.82) when compared with gilts from farm A. The heritabilities and additive genetic variances for behavioral traits were estimated with a linear animal model and were on a low level in farm A (h(2) = 0.11, SE = 0.07, and σ(2)a = 0.12 for aggressive attack and h(2) = 0.04, SE = 0.07, and σ(2)a = 0.02 for reciprocal fighting) and on a moderate level in farm B (h(2) = 0.29, SE = 0.13, and σ(2)a = 0.44 for aggressive attack and h(2) = 0.33, SE = 0.12, and σ(2)a = 0.27 for reciprocal fighting). For both aggressive attack and reciprocal fighting, genetic correlation of the same trait between farm A and farm B was 1.0. Therefore, aggressive behavior does not seem to be influenced by genotype × environment interactions. Under these circumstances aggressions in group housing can be reduced by genetic selection against aggressive behavior. Therewith, the welfare and health of sows will ultimately increase.