In high-producing dairy cows periparturient negative energy balance (NEB) triggers body fat mobilization, resulting in elevated blood levels of non-esterified fatty acids (NEFAs). Blood is dominated by the saturated fatty acids (SFA) palmitic (C16:0) and stearic acid (C18:0), which are associated with a negative effect on oocyte developmental competence. In contrast, the monounsaturated fatty acid (MUFA) oleic acid is harmless and is able to counteract the negative effect of saturated NEFAs on in vitro maturing oocytes. Since preantral follicles lack oleic acid-rich follicular fluid, we hypothesized that preantral follicles and oocytes may benefit from oleic acid-rich fat supplementation during NEB. Eight-month pregnant Holstein Friesian heifers were randomly divided in two groups to receive a standard, palmitic acid-rich (CTR, n = 5), or rumen-protected oleic acid-rich (UNSAT, n = 6), periparturient fat supplementation until 4 weeks post-calving. NEFA, beta-Hydroxybutyric acid and haptoglobin profiles in blood were monitored, and cumulus-oocyte-complexes (COCs) were via transvaginal ovum pick-up (OPU) collected at 8, 12, and 16 weeks postpartum for in vitro maturation, fertilization (day 0), and culture until day 8. Oleic acid supplementation increased C18:1 and reduced C16:0 levels in blood in comparison to CTR, during the peripartum period. Interestingly, the UNSAT group exhibited a 1.6-times higher oocyte yield in comparison to the CTR, but no difference in oocyte developmental competence between the groups. These findings suggest that peripartum oleic acid supplementation supports follicles and oocytes during NEB. Potential long-term benefits of oleic acid on fertility in dairy cows, in a higher number of animals, warrant further investigation.
