Abstract
BackgroundHeat stress adversely affects pig growth and reproduction performance by reducing feed intake, weight gain, farrowing rate, and litter size. Heat tolerance is an important characteristic in pigs, allowing them to mitigate the negative effects of heat stress on their physiological activities. Yet, genetic variation and signaling pathways associated with the biological processes of heat-tolerant pigs are currently not fully understood. This study examined differentially expressed genes and constructed gene co-expression networks on mRNAs of pigs under different heat-stress conditions using whole transcriptomic RNA-seq analyses. Semen parameters, including total sperm number per ejaculate, motility, normal morphology rate, droplets, and rejected ejaculate rate, were measured weekly on 12 boars for two time periods: thermoneutral (January to May), and heat stress (July to October). Boars were classified into heat-tolerant (n = 6) and heat-susceptible (n = 6) groups based on the variation of their ejaculate parameters across the two periods. RNA was isolated from the blood samples collected from the thermoneutral and heat stress periods for gene expression analysis.ResultsUnder heat stress, a total of 66 differentially expressed genes (25 down-regulated, 41 up-regulated) were identified in heat-tolerant pigs compared to themselves during the thermoneutral period. A total of 1041 differentially expressed genes (282 down-regulated, 759 up-regulated) were identified in the comparison between heat-tolerant pigs and heat-susceptible pigs under heat stress. Weighted gene co-expression network analysis detected 4 and 7 modules with genes highly associated (r > 0.50, p < 0.05) with semen quality parameters in heat-tolerant and heat-susceptible pigs under the effects of heat stress, respectively.ConclusionThis study utilized the sensitivity of semen to heat stress to discriminate the heat-tolerance ability of pigs. The gene expression profiles under the thermoneutral and heat stress conditions were documented in heat-tolerant and heat-susceptible boars. Findings contribute to the understanding of genes and biological mechanisms related to heat stress response in pigs and provide potential biomarkers for future investigations on the reproductive performance of pigs.
Highlights
Heat stress adversely affects pig growth and reproduction performance by reducing feed intake, weight gain, farrowing rate, and litter size
Semen quality parameters and group classification In this study, we utilized the change of semen quality parameters due to heat stress (HS) to distinguish heat-tolerant pigs from the population to document gene expression patterns of heat-tolerant and heat-susceptible pigs under TN and HS conditions
Results of the current study suggest that resistance to the suppression of immune functions and lipid metabolism induced by HS might contribute to heat tolerance in pigs
Summary
Heat stress adversely affects pig growth and reproduction performance by reducing feed intake, weight gain, farrowing rate, and litter size. Boars were classified into heat-tolerant (n = 6) and heat-susceptible (n = 6) groups based on the variation of their ejaculate parameters across the two periods. As global temperatures continue to increase, the swine industry faces severe challenges related to heat stress (HS). Being one of the major environmental challenges on agriculture, HS negatively affects the immune functions, metabolism, fertility, and welfare at every stage of the production cycle [1,2,3]. In pigs, HS negatively impacts productivity through increasing the whole-body insulin sensitivity and preventing adipose tissue mobilization [5]. Pigs are highly susceptible to increased environmental temperatures given a lack of effective sweat glands for thermoregulation and the presence of a thick layer of subcutaneous adipose tissue which reduces the heat exchange capacity [3]. Intense genetic selection for production traits has contributed to a reduction in heat tolerance due to the large amount of metabolic heat generated by higher producing animals [6,7,8]
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