106 Effect of Heat-Stress on Antral Follicle Count and Serum Concentration of Anti-Mullerian Hormone in Bos taurus Crossbred Beef Cows

Abstract

Anti-mullerian hormone (AMH) has become an important tool for the selection of donors with high antral follicle count and high superovulatory response for in vivo or in vitro embryo production programs. The serum concentration of AMH is becoming a suitable selection marker because it presents minimal variation during the oestrous cycle and is repeatable during multiple cycles. It is known that heat stress results in decreased production of reproductive steroid and protein hormones in stressed animals. Importantly, the effect of heat stress on the serum concentration of AMH is still unknown. The objective of this experiment was to evaluate the antral follicle count and AMH serum concentration levels during the spring to summer transition to assess the effect of heat stress in these parameters. Ten Bos taurus crossbred non-lactating beef cows (body condition 4–8 on 9-pt scale; mean = 6.7) were used in the experiment. Dominant follicle removal was performed 5 days before sample collection and antral follicle count. Blood was collected through caudal tail venipuncture in serum collection tubes. Antral follicle count was performed through trans-vaginal ultrasound imaging of ovaries where follicles ≥2 to 3 mm were counted. Serum AMH concentration was measured utilising the Bovine AMH ELISA kit AL-114. Blood sampling and antral follicle count was performed at midmonth during April, May, June, and July. Serum AMH and antral follicle count was analysed by ANOVA. Days with average temperature-humidity index (THI) >75 (mild stress) per month were 0/30, 6/31, 26/30, and 31/31 for April, May, June, and July, respectively. Days with average THI >79 (high stress) per month were 0/30, 0/31, 6/30, and 14/31 for April, May, June, and July, respectively. The total antral follicle count for both ovaries (mean ± SE) was 36.1 ± 4.20, 48.1 ± 7.19, 34.2 ± 4.19, and 46.5 ± 5.85 for April, May, June, and July, respectively. There was no difference (P = 0.1936) in antral follicle count between months. Serum AMH concentration (ng mL⁻¹) was 0.554 ± 0.14, 0.857 ± 0.21, 0.513 ± 0.12, and 0.575 ± 0.13 for April, May, June, and July, respectively. There was no difference (P = 0.3851) in AMH serum concentration between months. The concentration of AMH/follicle (AMH serum concentration/antral follicle count; ng mL⁻¹) was 0.0150 ± 0.0028, 0.0166 ± 0.0018, 0.0152 ± 0.0036, and 0.0123 ± 0.0025 for April, May, June, and July, respectively. There was no difference (P = 0.7385) in the concentration of AMH/follicle between months. Results of the experiment showed that heat stress does not affect antral follicle count, AMH serum concentration, or concentration of AMH/follicle and suggest that granulosa cell function in terms of AMH production is not affected by heat stress during the spring to summer transition.