Effects of prolonged unsaturated fatty acid supplementation on reproductive competence and metabolic profiles in serum and follicular fluid of Holstein heifers

This study evaluated the effects of a 120-d dietary supplementation with unsaturated fatty acids from soybean grain and flaxseed on oocyte quality, in vitro embryo quality and production, and the metabolic profiles of blood and follicular fluid in Holstein heifers. Twenty-four heifers were assigned to the following treatments: a control diet (CON) and diets supplemented with whole raw soybeans (WRS) or flaxseed (FLX), both formulated to increase ether extract content to approximately 4.5 % dry matter (DM). Growth performance, serum metabolites, follicular fluid composition, and in vitro embryo production were assessed. Data were analyzed as repeated measures modeling the fixed effects of treatment, time, and their interaction. Treatment means were compared through orthogonal contrasts (CON vs. WRS+FLX and WRS vs. FLX). Heifers in the supplemented groups exhibited reduced average daily gain compared to the control group. Serum glucose concentrations were lower, while total cholesterol tended to be lower and low-density lipoprotein cholesterol tended to be higher in supplemented groups, indicating shifts in lipid metabolism. Follicular fluid analyses revealed decreased triglyceride and a tendency to decreased urea levels in supplemented groups. Oocyte quality improved in heifers receiving fat supplementation, as indicated by a higher proportion of viable oocytes, while no differences were observed in the cleavage rates and embryo production. These findings suggest that unsaturated fatty acids can modulate metabolic parameters and enhance oocyte viability in Holstein heifers, although their effects on embryo production remain inconsistent. Further research is needed to optimize fatty acid supplementation strategies for improving reproductive efficiency in dairy cattle.