Higher Tolerance of Min Pigs Under Cold Stress: An Assessment from Reproduction Perspective

Raising Min pigs（MPs） in northern China is challenging, because of harsh environmental conditions in winter. There is a hypothesis that MPs can tolerate cold stress better than Large White pigs（LWPs） and their oocyte competence is particularly protected. Over a period of 3 years, multiple cohorts of MPs and LWPs under different environmental conditions were studied in this paper. Follistatin（FST） serum level was used as a marker for swine oocyte competence. Oocytes were collected from the swine and their maturation rate, cleavage rate and blastocyst rate were measured. Lastly, mRNA expression in ovary and longissimus dorsi for the genes FST, luteinizing hormone receptor（LHR） and cold-inducible RNA-binding protein（CIRP） was measured. Under cold stress, serum follistatin concentrations of both LWPs and MPs were markedly increased, and they were more in LWPs than in MPs. However, oocyte competence was found to be unaffected by cold stress in MPs. It was found that in a separate group of LWPs, oocyte competence was lower in samples collected in winter than that in other seasons. Interestingly, follistatin levels in the follicular fluid of MPs showed no change with cold stress, and serum follistatin levels were increased in sows. Gene expression analysis showed a significant reduction in FST, LHR and CIRP expressions under cold stress in longissimus dorsi, but not in the ovaries. It was found that MPs were better able to maintain oocyte competence under cold stress, which might be due to improved regulation of follistatin in follicular fluid, and MPs appeared likely an adaptation to the harsh conditions that they faced under domestication in northern China.