348 ANTI-MÜLLERIAN HORMONE AND SUPEROVULATORY RESPONSE IN DONOR COWS MANAGED IN 2 SEMIARID ENVIRONMENTS IN NORTHWEST MEXICO

Abstract

An embryo transfer program in cows relies on the superovulatory (SPO) response after receiving a hormonal treatment. Anti-Müllerian hormone (AMH) has been proposed as an endocrine marker associated to superovulation; however, the SPO response of donors has also been influenced by the environment. Thus, objective herein was to evaluate effects of serum AMH levels on number of ovarian follicles (NOF), corpora lutea (CL), and transferable embryos (TE) in superovulated donor cows managed under summer or winter conditions in northwest Mexico. Fifty-two cows in a random stage of the oestrous cycle were used in this study. All cows received an Eazi-Breed CIDR cattle insert (1.384 g of progesterone; Zoetis, USA), and 2.76 mg of oestradiol benzoate (Sigma-Aldrich, St. Louis, MO, USA) plus 50 mg of progesterone (Vetoquinol, Canada) given i.m. to synchronize follicular wave emergence (Day 0). The SPO treatment started on Day 4 with decreasing doses (120, 80, 40, and 20 mg) of Folltropin-V (Vetoquinol, Canada) injected twice daily until Day 7. Artificial insemination was performed on days 8 p.m. and 9 a.m. and ova/embryos were collected on Day 15. Transrectal ultrasonography was done on Days 8 and 15 to determine the number of follicles >9 mm in diameter on Day 8 and CL on Day 15, respectively. Blood samples were collected on the first day of SPO treatment (Day 4) to measure serum AMH concentrations, which served to classify cows as high- (>400; n = 29) and normal-AMH donors (100–400 pg mL^–1; n = 23). A mixed effects model was used to analyse SPO response in cattle including level of AMH and season as fixed effects, age as covariate, and sire as random. Level of AMH, season, and their interaction resulted as significant (P < 0.05) sources of variation. Pearson correlations were determined between serum AMH concentrations and SPO response for summer and winter. Average serum levels of AMH were 471.5 ± 70.4 and 1194.2 ± 57.3 pg mL^–1 during summer and winter, respectively. The SPO response differed in high- and normal-AMH donor cows (P < 0.05). Mean (± s.e.m.) NOF, CL, and TE were 19.8 ± 1.0, 12.8 ± 0.6, and 7.3 ± 0.5 for high-AMH donors, and 10.9 ± 1.6, 6.5 ± 1.9, and 3.8 ± 1.1 for normal-AMH donor cows, respectively. Environment of donor cows also influenced SPO response as NOF, CL, and TE increased 42, 50, and 45%, respectively, during winter compared with summer (P < 0.05). Correlations among NOF, CL, and TE with serum AMH levels were moderate for donor cows managed during winter (0.657, 0.523, and 0.431, respectively; P < 0.01), and low in cows managed during summer (0.309, 0.195, and 0.085, respectively; P > 0.05). Results from this study indicated that SPO response in donor cows is associated with serum concentrations of AMH; however, the relationship among these variables appears to be affected in the summer when drought and severe heat stress are common. We concluded that under winter conditions of northwest Mexico, the serum levels of AMH should be considered as an endocrine marker associated with ovarian traits indicative of the SPO response in donor cows.