Taxa de prenhez em vacas mestiças submetidas ao protocolo de IATF e aplicação de análogo de GnRH 12 dias após a IA

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 PGF2α (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 12th day after AI. On the 35th 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.

Impact of breed, body score and animal category on the pregnancy rate of bovine females under IATF management

“…The reduction in production costs, without interference in production performance, means improvement in the efficiency of the system. Gottschall and Silva (2018) reported a pregnancy rate of 57.6% in beef heifers using third use progesterone devices, a result similar to that found in this study. Gottschall et al (2009) observed pregnancy rates of 61.1% and 49.7% in Aberdeen Angus cows using intravaginal progesterone devices, of 1st and 2nd use , respectively, showing that the reuse of the progesterone device in the protocol TAI is also effective in lactating cows with calf at foot.…”