Pregnancy rate in crossbred cows subjected to FTAI protocol and application of a GNRH analog 12 days after AI1

Abstract

This study aimed to evaluate the effect of GnRH administered 12 days after FTAI on pregnancy rate and progesterone levels in crossbred beef cows. Fifty-nine non-pregnant crossbred cows (Bos taurus indicus x Bos taurus taurus) previously selected by gynecologic examination with a body condition score (BCS) of 3.0 (scale of 1 - 5). Cows were randomly assigned to two treatments: TEB (n = 30), on day 0, an intravaginal progesterone releasing device (Primer^®) was inserted and cows received i.m. 2.0 mg of estardiol benzoate (EB, Estrogin^®); on day 8, the PRIMER was removed and cows received i.m. 300 IU of eCG (Novormon^®) and 0.15 mg of PGF_2α (Prolise^®); on day 9, cows received i.m. 1 mg of EB. FTAI was carried out 48-56 hours after PRIMER removal; and TEBGnRH12 (n = 29): similar protocol to TEB, but with administration of 25 µg GnRH (Lecirelin, Gestran Plus^®) on the 12^th day after AI. On the 35^th day after AI, diagnosis of pregnancy was performed by transrectal ultrasound. The pregnancy rate was analyzed by logistic regression. The results showed that 53.33% of the cows (16/30) in TEB and 37.93% (11/29) in TEBGnRH12 became pregnant after the first service. No significant difference was found among the pregnancy rate of animals in the treatments (P> 0.05). There was no difference between the P4 concentrations (TEB = 3.88 ng/mL and TEBGnRH12 = 3.12 ng/mL) among the heifers in the treatments (P> 0.05). The administration of GnRH analogs 12 days after TAI did not influence pregnancy rate or the progesterone concentration.