108 EFFECTS OF UTILIZATION OF SUBCUTANEOUS IMPLANTS OF GnRH AGONISTS (DESLORELIN) ON OVARIAN ACTIVITY AND HORMONAL PROFILE DURING THE PERIOD OF IMPLANTATION AND AFTER REMOVAL IN NELORE COWS (BOS INDICUS) WITH A TOTAL IMPLANT TREATMENT OF 70 DAYS

Abstract

The aim of the present study was to evaluate the effects of subcutaneous implants of deslorelin (GnRH agonist-Suprelorin^® 4.7 mg) on follicular dynamics and plasma profile of FSH, LH, and progesterone (P4) during the last 20 days of an implantation period of 70 days and after the removal of the implant until the detection of the first ovulation in Nelore cows (Bos indicus). Seven animals had their ovulation synchronized. At the day of the detection of ovulation they received subcutaneous implant of deslorelin. In the last 20 days of the period of treatment, ultrasound scans were taken every 2 or 3 days to characterize the follicular dynamics according to diameter: I (<4 mm), II (4–6 mm), and III (>6 mm). Blood samples were collected to measure plasma concentrations of FSH, LH, and P4. Results were tested by ANOVA, and difference between means was defined using Tukey’s test with significance levels of 0.05. During the 70 days of deslorelin treatment, none of the animals ovulated, despite the implant not suppressing all follicular development. The ultrasound finding was confirmed by P4 plasma concentrations (range: 0.05–0.31 ng mL^–1). The normal P4 plasma concentration expected in cycling Nelore cows is about 3.8 ng mL^–1 (Satrapa et al. 2010 Reprod. Anim. Dom. 45, 881–887). During the last 20 days of treatment, 4 animals presented follicular development with max diameter ranging through 4 to 6 mm, whereas in the 3 remaining animals, the observed diameter ranged through 9 to 12 mm. The secretion of FSH and LH was not entirely suppressed during the study (range: 1.69–1.39 and 1.37–1.07 ng mL^–1, respectively). After the removal of the deslorelin subcutaneous implant, the period of restoration of the ovulatory capacity was 29 days, and the mean diameter of the preovulatory follicle was 12.5 mm. The P4 plasma concentrations during this time were low (range: 0.15–0.09 ng mL^–1). During the recovery period, the phenomenon of follicular codominance and double ovulation in 2 animals (2/7) was observed. From the results obtained, it can be concluded that the total implant treatment of 70 days with deslorelin in cows inhibits ovulation by not allowing LH surge, although the follicular development is not completely depressed.

The financial support of FAPESP, Fundunesp, and CNPq are acknowledged.