Abstract
Variation in cryotolerance exists between embryos from different animal breed, species and management conditions. Reduced tolerance to chilling and cryotolerance of oocytes and embryos has been associated with greater cytoplasmic lipids (Kim et al., 2001; Seidel, 2006). Previous studies in the cow have demonstrated nutrition-induced modification of follicular components. Trans-10, cis-12 conjugated linoleic acid (CLA) was identified as a potent inhibitor of milk fat synthesis in lactating cows (Baumgard et al., 2000) and inclusion of CLA in bovine embryo culture medium improved post-thaw embryo survival (Pereira et al., 2007). Dietary supplementation of cows with CLA could alter oocyte fatty acid metabolism, oocyte lipid composition and embryo cryotolerance, and responses may be different between Bos indicus and Bos taurus breeds of cattle. Therefore, a series of experiments were conducted to evaluate effects of dietary CLA supplementation of cows on (1) milk fat depression in lactating Holstein cows, (2) follicle and oocyte production and lipid content of oocytes from Brahman and Holstein cows, (3) mRNA expression of genes involved in lipid metabolism in oocytes from Brahman and Holstein cows and (4) cryosurvival of in vitro-produced embryos from CLA-supplemented oocyte donor cows. Milk fat was depressed by 10.1% in lactating Holstein cows fed CLA. Follicle, oocyte and embryo production of cows were not influenced by CLA supplementation. Dietary supplementation of cows with CLA before oocyte collection did not influence cryotolerance of in vitro-produced embryos or expression of genes in oocytes involved in lipid metabolism. Lipid content of oocytes was not influenced by CLA supplementation. The ovarian response to dietary CLA was similar among Brahman, Holstein and crossbred beef cows. The highly regulated mechanisms involved in fatty acid uptake by ovarian components may help explain the lack of ovarian response to dietary CLA in the current study.
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