158 Optimal time of AI and changes in vaginal mucus characteristics relative to the onset of standing oestrus in Beetal goats

Abstract

The aim of this study was to determine the optimum time of AI and its relationship with vaginal mucus characteristics relative to the onset of standing oestrus in Beetal goats. For this purpose, goats (n = 257) were synchronised for oestrus by administering two doses of prostaglandin F_2α (0.075 mg intramuscularly, d+ cloprostenol, Dalmazin) 11 days apart during the breeding season (September-December, 2016-2018). The onset of standing oestrus was determined using apronised bucks. Intracervical inseminations were performed at 0 (n = 28), 12 (n = 84), 24 (n = 101), and 36 h (n = 44) after the onset of standing oestrus using chilled semen (diluted in skim milk at 200 × 10⁶ spermatozoa per 0.5-mL dose). Color (transparent = 1, turbid = 2, cheesy/whitish = 3), consistency (thin = 1, thick = 2), and volume (excess = 1, scant = 2) of the vaginal mucus in goats were observed at the time of inseminations and graded to determine the cumulative mucus score. Resistive index of vaginal mucus (R-value) was monitored at the time of AI using a Draminski heat detector. The intervals to the onset of oestrus among different months of synchronisation, cumulative mucus score, and vaginal electrical resistance at different times of AI were compared using one-way analysis of variance. Pregnancy rates at different times of AI were compared using chi-square analysis, and the Pearson coefficient of correlation was used to correlate mucus color, consistency, and volume with the cumulative mucus score. Following the second prostaglandin F_2α administration, the interval to the onset of standing oestrus was longer (P < 0.05) in goats synchronised in December than in those synchronised from September to November. The pregnancy rate was lower (P < 0.05) in goats inseminated at 0 h (28.6%) compared with those inseminated at 12 (58.3%), 24 (56.4%), and 36 h (54.5%). However, the pregnancy rates were similar in goats inseminated at 12, 24, and 36 h (P > 0.05). Odds for pregnancy rate at 12 h were 3.5, 1.08, and 1.16 times higher than those at 0, 24, and 36 h, respectively. Relative to the time of AI, the cumulative mucus scores varied (P < 0.05), and changes in mucus colour and consistency were more highly correlated (r = 0.832 and 0.793, respectively; P < 0.05) with cumulative mucus score than the mucus volume (r = 0.588). Relative to the onset of standing oestrus, the R-value of the mucus was lower at 12 h than at 0 and 36 h (P < 0.05); however, there was no change in R-value of the mucus at 12 and 24 h. In conclusion, the optimum time to inseminate Beetal does using chilled semen is 12 h following the onset of oestrus, whereas cumulative mucus score and R-value can be used as alternatives if the time of the onset of oestrus is not known.