122 Effect of gonadotropin-releasing hormone plus 7-day progesterone (CIDR) with or without eCG on follicular dynamics, estrus response, and pregnancy rate in anestrous Beetal goats during nonbreeding season under subtropical conditions

Abstract

Oestrus induction is a challenging task during the nonbreeding season in goats. Therefore, our objective was to evaluate the efficacy of gonadotropin-releasing hormone (GnRH) plus a 7-day CIDR-based protocol with or without eCG for the induction of oestrus and fertility in acyclic Beetal goats during the nonbreeding season under subtropical conditions. Based on the absence of corpus luteum via ultrasonography, goats (n = 56; mean weight = 32.8 ± 0.5 kg; body condition scre = 2.5 ± 0.1) were inserted with a CIDR (300 mg progesterone) along with GnRH (Day 0), and randomly treated either with eCG (400 IU; n = 35) or without eCG (control; n = 21) on Day 7. The CIDR was removed on Day 7 and all does were administered single dose of prostaglandin F_2α (75 µg cloprostenol; Fatro, Italy). Following CIDR insertion, ovarian follicular dynamics was monitored daily through a 7.5-MHz transrectal transducer (Honda HS 1500, Japan) until ovulation in a subset of eCG (n = 11) and control goats (n = 10). Oestrus was detected at every 12 h after CIDR removal with aproned bucks and does were bred naturally. Pregnancy was detected 25 days after breeding by transrectal ultrasound. Data were analysed by t-test, ANOVA, and Chi-squared test using SPSS (version 20.0, SPSS Inc., Chicago, IL, USA). Oestrus occurred more often following CIDR removal in eCG v. control goats (94 v. 57%; P < 0.05). Similarly, onset of oestrus was earlier (36.0 ± 2.1 v. 54.2 ± 4.7 h; P < 0.05) and the duration of oestrus was longer in eCG v. control goats (i.e. 30.2 ± 1.3 v. 22.1 ± 2.3 h; P < 0.05). However, diameter of preovulatory follicles and interval to ovulation after CIDR removal were similar between eCG and control goats (P > 0.05). In contrast, growth rate of preovulatory follicle after CIDR removal until ovulation in eCG goats was greater, and ovulation rate was higher than control goats (0.7 ± 0.1 v. 0.3 ± 0.1 mm/day; 2.2 ± 0.2 v. 1.4 ± 0.2, respectively; P < 0.05). In eCG goats, the dominant follicle grew rapidly between Days 8 to 9 (P < 0.05), whereas within control goats the dominant follicle grew at consistent rate (P > 0.05). After CIDR removal, percentage of ovulating goats in eCG was higher as compared to the control group (100 v. 44%; P < 0.05). Within control goats, size of the dominant follicle in ovulatory goats was greater at the time of CIDR removal than anovulatory goats (5.7 ± 0.3 v. 5.0 ± 0.15 mm; P < 0.05), whereas wave emergence tended to be earlier after CIDR insertion in anovulatory goats (4.2 ± 1 v. 2.6 ± 0.4 days; P = 0.09). Pregnancy rate 25 days postbreeding did not differ between eCG and control goats [i.e. 49% (16/33) v. 25% (3/12); odds ratio 2.9/1; P > 0.05]. In conclusion, the eCG protocol resulted in higher oestrus response, ovulation rate, and 3 times higher pregnancy rate in anestrous goats during the nonbreeding season.