Genetic improvement programs in livestock: swine testing and genetic evaluation system (stages)

Genetic Parameters for Tolerance to Heat Stress in Crossbred Swine Carcass Traits

Data for loin and backfat depth, as well as carcass growth of 126,051 three-way crossbred pigs raised between 2015 and 2019, were combined with climate records of air temperature, relative humidity, and temperature-humidity index. Environmental covariates with the largest impact on the studied traits were incorporated in a random regression model that also included genomic information. Genetic control of tolerance to heat stress and the presence of genotype by environment interaction were detected. Its magnitude was more substantial for loin depth and carcass growth, but all the traits studied showed a different impact of heat stress and different magnitude of genotype by environment interaction. For backfat depth, heritability was larger under comfortable conditions (no heat stress), as compared to heat stress conditions. Genetic correlations between extreme values of environmental conditions were lower (∼0.5 to negative) for growth and loin depth. Based on the solutions obtained from the model, sires were ranked on their breeding value for general performance and tolerance to heat stress. Antagonism between overall performance and tolerance to heat stress was moderate. Still, the models tested can provide valuable information to identify genetic material that is resilient and can perform equally when environmental conditions change. Overall, the results obtained from this study suggest the existence of genotype by environment interaction for carcass traits, as a possible genetic contributor to heat tolerance in swine.

Production performance, carcass composition, and adipose tissue traits of heavy pigs: influence of breed and production system

Both breed and production systems are responsible for production efficiency and quality traits of pork. Effects of breed and production system within breed on growth, body fatness, and adipose tissues traits were assessed in the pure Basque (B, nonselected, local French) and conventional Large White (LW) breeds, reared either in a conventional (C, slatted floor), alternative (A, indoor straw bedding and outdoor area), or extensive (E, free range) system. A total of 100 castrated males were produced in 2 replicates, each involving 50 pigs distributed in 5 treatments based on breed and production system (i.e., BC, BA, BE, LWC, and LWA [10 pigs/group and per replicate]). From 35 kg BW to slaughter at around 145 kg BW, the BC, BA, LWC, and LWA pigs received the same growing and finishing diets, whereas the BE pigs had free access to the natural resources of the E pen and received a standard growing-finishing diet at restricted allowance according to the farming practices of the B pork chain. The B pigs had lower (P < 0.001) ADG and G:F than the LW pigs and were much older (P < 0.001) at slaughter. The LWA pigs had similar ADG but lower (P = 0.03) G:F than the LWC. Within the B breed, the BA had higher (P = 0.04) and the BE lower (P < 0.001) ADG compared with BC pigs. The B pigs had a higher (P < 0.001) carcass dressing an exhibited around 2-fold higher (P < 0.001) back fat proportion, perirenal fat weight and LM lipid content than the LW pigs. Compared with C, the A system decreased (P = 0.04) carcass dressing within LW but did not influence carcass traits within B pigs. The E system decreased (P ≤ 0.05) carcass dressing, back fat proportion, and LM lipid content in BE compared with BC pigs. The B pigs exhibited larger (P < 0.001) adipocytes in both subcutaneous adipose tissue (SCAT) and LM than the LW pigs. Malic enzyme activity was higher in SCAT of B than LW pigs despite their greater fatness, and was higher (P ≤ 0.01) in BA but lower (P < 0.001) in BE than in BC pigs. The B pigs had higher (P < 0.001) MUFA but lower (P ≤ 0.006) SFA and PUFA fatty acid percentages in SCAT than the LW pigs. Compared with C, the A system had scarce influence on FA composition within each breed, whereas the E system led to lower (P = 0.015) SFA and greater (P < 0.001) PUFA in SCAT of the B pigs. Altogether, the E production system can counteract the genetic potential of B pigs for growth rate but also body fatness.

Comparison of muscle transcriptome between pigs with divergent meat quality phenotypes identifies genes related to muscle metabolism and structure

BACKGROUND

Meat quality depends on physiological processes taking place in muscle tissue, which could involve a large pattern of genes associated with both muscle structural and metabolic features. Understanding the biological phenomena underlying muscle phenotype at slaughter is necessary to uncover meat quality development. Therefore, a muscle transcriptome analysis was undertaken to compare gene expression profiles between two highly contrasted pig breeds, Large White (LW) and Basque (B), reared in two different housing systems themselves influencing meat quality. LW is the most predominant breed used in pig industry, which exhibits standard meat quality attributes. B is an indigenous breed with low lean meat and high fat contents, high meat quality characteristics, and is genetically distant from other European pig breeds.

METHODOLOGY/PRINCIPAL FINDINGS

Transcriptome analysis undertaken using a custom 15 K microarray, highlighted 1233 genes differentially expressed between breeds (multiple-test adjusted P-value<0.05), out of which 635 were highly expressed in the B and 598 highly expressed in the LW pigs. No difference in gene expression was found between housing systems. Besides, expression level of 12 differentially expressed genes quantified by real-time RT-PCR validated microarray data. Functional annotation clustering emphasized four main clusters associated to transcriptome breed differences: metabolic processes, skeletal muscle structure and organization, extracellular matrix, lysosome, and proteolysis, thereby highlighting many genes involved in muscle physiology and meat quality development.

CONCLUSIONS/SIGNIFICANCE

Altogether, these results will contribute to a better understanding of muscle physiology and of the biological and molecular processes underlying meat quality. Besides, this study is a first step towards the identification of molecular markers of pork quality and the subsequent development of control tools.

Genetic influences on reproductive performance

The potential for genetic improvement of reproductive performance in pigs is great. Improvement can be achieved by increased commercial use of F1 hybrid females produced by crossing lines with excellent reproductive performance and by selection within nucleus populations of these lines for improved reproduction as well a for growth and carcass characteristics. The value of incorporating reproductive traits in selection programs is critically dependent on the relative economic values of fat (or lean) and of extra pigs produced. There is widespread agreement that litter size is the first choice as both the selection objective and the criterion to improve reproductive performance, on economic, genetic, and ease of measurement grounds. Although there are few examples of successful response to selection for increased litter size in pigs (exceptions being the University of Nebraska selection experiment and results achieved by hyperprolific selection schemes), overall results do not suggest that selection for litter size is impossible, only that it is difficult with limited resources. Artificial insemination is being used increasingly by pig breeding companies to accelerate rates of genetic improvement and to improve dissemination. Combining data from genetically connected herds and analyzing with BLUP computer programs to make efficient use of information on relatives makes selection for litter size feasible while maintaining selection pressure for growth and carcass traits. Although selection for lifetime productivity is impractical today, the knowledge and data accumulated from successful breeding programs for litter size may help make it the selection objective of the future. Meanwhile, the search continues for useful indirect criteria for selection, from testis size to molecular markers, and scientists are working with highly prolific breeds of Chinese pigs to better understand the physiologic and genetic basis of large litter size.