112 Follicular dynamics and oestrus response of Alpine goats with oestrus/ovulation synchronized during the early transitional reproductive phase using gonadotrophin given early or late

Abstract

Oestrus and ovulation synchronization (E/OS) regimens for fixed-timed breeding are useful when consistently eliciting ovulation. Early synchronization in the reproductive season promotes unreliable oestrus behavioural and physiologic response due to insufficient ovarian priming. In ruminants, equine (eCG) or human chorionic gonadotrophin (hCG) has FSH bioactivity or elicits ovulation, correspondingly. Hence, 120 and 60 IU of eCG and hCG, respectively, are included in goat E/OS regimes. This experiment addresses the time when eCG/hCG (CG) is given relative to progestagen (P4) withdrawal and its effect on oestrus and ovulation. Fourteen non-lactating, Alpine breed goats, ranging from 1 to 6 kiddings, averaging ± s.d. 3.9 ± 2.0 years of age, and 56.3 ± 5.0 kg of bodyweight (BW), and body condition score (BCS) of 2.6 ± 0.2, were evaluated early in the transitional reproductive phase (12 h daylight:12 h darkness). E/OS was accomplished with 12 day of P4 (200 mg) exposure by intravaginal insert. Three treatments were evaluated: Traditional (T; n = 4) did not receive CG and served as the control group; early (E; n = 5) received CG 24 h before P4 removal; and reverse (R; n = 5) received PGF_2α 24 h before P4 withdrawal as well as CG concurrent with P4 withdrawal. Oestrus response to E/OS was evaluated 24 h after breeding using epididymectomized bucks. Ovaries were scanned by transrectal ultrasound (Aloka SSD-500V/7.5-MHz linear array probe) for 4 consecutive days starting with the first i.m. injection of 1.0 mL of PGF_2α or 1.5 mL of CG. Images were digitized (MediCapture™) for later morphometry. The absence of effect (P > 0.05) from concomitant variables age, BW, BCS, and parity was ascertained using a logistic regression model (JMP/SAS v15; SAS Institute Inc.). Ovulation, defined as the disappearance of the largest (>7 mm) preovulatory follicle on a subsequent observation, was 100, 80, and 100%; and the average ± s.e. number of ovulations per goat was 2 ± 0.41, 1 ± 0.32, and 1.3 ± 0.49 (P > 0.05). Table 1 summarises follicular size documented of 122 observations of ovulatory areas. Graafian follicle location was not different for left or right ovaries (P > 0.05). Oestrus behavioural response to each E/OS treatment (T, E, or L) up to 24 h after P4 removal was 50, 80, and 80% (P > 0.05), respectively. In summary, oestrus response and ovulation were not affected by the variables studied. In this experience the timing of CG was not relevant.

Table 1.  Mean diameter (± SE; mm) of nonovulatory and preovulatory follicles on left (L) and right (R) ovaries