49 EFFECTS OF DIETARY CONJUGATED LINOLEIC ACID SUPPLEMENTATION ON BOVINE OOCYTE LIPID METABOLISM, LIPID COMPOSITION, AND EMBRYO CRYOTOLERANCE

Reduced tolerance to chilling and cryotolerance of oocytes and embryos has been associated with greater cytoplasmic lipids. 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, and inclusion of CLA in bovine embryo culture medium reduced embryo lipid content and improved post-thaw embryo survival. 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 cattle. Therefore, a series of experiments were conducted to evaluate effects of dietary CLA on bovine oocyte lipid content and lipid metabolism and cryosurvival of in vitro-produced embryos from CLA-supplemented oocyte donor cows. Lactating Holstein cows (n = 39) were supplemented 100 g per head/d CLA or Ca salts of palm oil to determine effects of dietary CLA on milk production and milk composition. Nonlactating Holstein (n = 8) and Brahman (n = 17) cows were individually supplemented with 150 g per head/d CLA or no lipid supplement. Cumulus-oocyte complexes (COC) were collected after 41 ± 1 day of CLA supplementation, and mRNA was isolated for qPCR. Relative gene expression in COC from CLA- and control-fed cows was evaluated for genes involved in lipid metabolism (CPT1, FADS2, and PPARα). Crossbred (Angus × Red Angus × Brangus) cows (n = 28) were randomly allotted to a 2 × 2 factorial experiment and fed 150 g per head/d CLA or no lipid supplement. Oocytes were collected (Day 129 and 143 of CLA supplementation), matured, fertilized, and cultured in vitro for 7 days in serum-free culture medium. Embryos were cryopreserved in individual 0.25-mL plastic straws containing 1.5 M ethylene glycol using a slow-cooled method. Post-thaw survival and hatching were evaluated using a 24-h in vitro culture (mSOF with 5% FBS) assay. Milk yield, milk composition, and Nile Red intensity were analysed using the GLM procedure of SAS (SAS Institute Inc., Cary, NC, USA). Follicle and oocyte responses were analysed with the Mixed procedure of SAS. Relative gene expression of COC was evaluated using the REST 2009 Software. In vitro embryo production, post-thaw survival, and hatching rates were analysed using Chi Square. Milk fat was depressed (P < 0.001) by 10.1% in lactating Holstein cows fed CLA. Dietary supplementation of Holstien and Brahman cows with CLA did not alter expression of genes (CPT1, FADS2, and PPARα) in COC. Dietary supplementation of crossbred cows with CLA before oocyte collection did not influence cryotolerance of in vitro-produced embryos. Lipid content of oocytes (measured by Nile Red florescence) and follicle, oocyte, and embryo production was not influenced by CLA supplementation of Holstein and Brahman 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.