134 FOLLICULAR DYNAMICS OF Gyr AND HOLSTEIN OOCYTE DONORS KEPT UNDER TROPICAL CONDITIONS

Abstract

Bovine in vitro production is highly relevant for dairy systems in Brazil, and the main breeds used as oocyte donors are Gyr (G) and Holstein (H). This study aimed to evaluate the ovarian follicular dynamics of G and H oocyte donors kept under tropical conditions to detect differences that could guide improvement of follicular wave synchronization protocols for ovum pickup. Fourteen cyclic cows (6 H and 8 G), assessed twice each (after a 14-day interval), had their oestrus cycle synchronized by the use of 1.0 g of progesterone via intravaginal device (Ourofino, Brazil) and administration of 2 mg of oestradiol benzoate (EB; Day 0). Withdrawal of progesterone device was followed by 7.6 mg of cloprostenol administration (Day 7); EB (1 mg) was administered after 24 h (Day 8, 0 h), and the animals were evaluated every 12 h by ultrasound for 6 days (0–132 h). All evaluations are reported regarding EB administration (0 h). Videos from each ovary were stored and processed using the ImageJ software (http://rsb.info.nih.gov/ij), by measuring the diameter of each visualised follicle. All procedures were approved by local ethics committee. Ovulation time (G = 42.0 ± 8.3; H = 42.5 ± 6.2), ovulatory follicle (F1) diameter (G = 11.5 ± 1.8; H = 12.4 ± 2.0), and F2 diameter (G = 7.2 ± 1.9; H = 7.4 ± 2.7) did not differ (P > 0.05) between breeds. Growth rate (mm day^–1) after ovulation was similar (P > 0.05) between breeds for each follicle (F1 = G: 0.6 ± 0.2, H: 0.8 ± 0.1; F2 = G: 0.5 ± 0.1 H: 0.4 ± 0.1, F3 = G: 0.2 ± 0.1, H: 0.3 ± 0.1). In H group, the F1 growth rate was higher (P < 0.05) than F2 and F3, but there was no difference (P > 0.05) in G group. Follicle deviation was identified 120 h after EB in the G group (~78 h after ovulation) and 132 h in the H group (~90 h after ovulation), and at that time F1, F2, and F3 follicle diameters were 8.0 ± 0.3, 6.6 ± 0.5, and 5.3 ± 0.3 for G (120 h), respectively; 8.8 ± 0.7, 7.2 ± 0.4, and 6.2 ± 0.3 for H (132 h), respectively. There was no difference between the size of F1, F2, and F3 between breeds at any time, except at 132 h, when H F3 was higher (P < 0.05) than G F3. Regarding the follicular population, follicles smaller than 3 mm were more numerous in G animals at all evaluated moments, and differed at 0 (G = 7.1 ± 1.1; H = 2.5 ± 0.5) and 132 h (G = 5.6 ± 0.8; H = 1.5 ± 0.3). Number of follicles between 3 and 8 mm increased in H compared to G at 24 (14.4 ± 1.0), 36 (15.7 ± 1.3), and 132 h (18.3 ± 1.4). Comparing 3- and 8-mm follicles in G between times, an increase (P < 0.05) in number was detected from 36 h onwards, comparedto 0 h (0 h: 9.2 ± 1.0; 36 h: 13.6 ± 1.4). This increase was not significant in H group (0 h: 13.7 ± 1.1; 132 h: 18.3 ± 1.4). The main findings of this study are that the moment of deviation and the population of follicles smaller than 3 mm and between 3 and 8 mm differs from Gyr and Holstein oocyte donors. Those observations suggest ovum pickup is better performed slightly later in Holstein donors than in Gyr, and can contribute to improvement of follicular wave synchronization protocols for each of the breeds in tropical conditions.

Study supported by FAPERJ, Embrapa and CNPq.