130 ANTRAL FOLLICLE COUNTS, VULVA WIDTH, AND SERUM ANTI-MULLERIAN HORMONE CONCENTRATIONS IN BOVINE FEMALES OF THE TABAPUÃ BREED

Bovine genetic selection for fertility is difficult in part due to the low heritability of fertility traits and to the extension of the calving interval and the productive life length inherent to this species, which makes it harder to identify superior individuals from their records. In this regard, it is feasible to try to identify characteristics that are easy to detect and may be linked to superior reproductive efficiency as early as possible in females. The objective was to evaluate the possible relationships between vulva width, antral follicle counts (AFC), and the serum concentrations of anti-Mullerian hormone (AMH). Tabapuã (a Brazilian Zebu breed) heifers (n = 155) and cows (n = 422) from 4 herds were used in the study in which all antral follicles ≥3 mm were counted directly with an ultrasound unit. Follicle counts were classified into 2 classes, based on the methodology proposed by Burns et al. (2005) in dairy cattle, such that the low and intermediate AFC classes were merged into one class (low; n = 245) and the high and very high into another (high; n = 332). The vulva width was determined by measuring the distance between the lateral borders of the vulva with a digital caliper placed at a 90-degree angle from the half point of the rima vulvae. Single blood samples were collected from a subgroup of animals (n = 220) and the serum frozen (–20°C) after centrifugation for the AMH analysis, which was performed by specific bovine ELISA (Ansh Laboratories, Webster, TX, USA) test. All statistical analyses were performed with SAS (SAS Institute Inc., Cary, NC, USA). Data was submitted for analyses of variance using the PROCGENMOD procedure. Vulva width was larger (P = 0.02) in the class of animals of the high AFC (8.73 ± 0.11 cm) in comparison with those of the low AFC (8.39 ± 0.09 cm), considering the larger sample (n = 591). In the subsample (n = 220) the concentration of AMH was higher (P < 0.0001) in the high AFC class females (1.15 ± 0.07 ng mL–1; n = 95) in comparison with the low AFC class (0.50 ± 0.06 ng mL–1; n = 125). Vulva width, AFC, and AMH serum concentrations were interrelated and likely fertility indicative phenotypes under the present experimental conditions and should be further evaluated in larger samples in order to be considered in bovine genetic selection.