Effects of temporary calf removal and eCG on pregnancy rates to timed-insemination in progesterone-treated postpartum Nellore cows

Abstract 

The objective was to evaluate the effects of temporary calf removal (TCR), eCG administration, or both, in a progesterone-based protocol. Suckled Nellore cows (40–80d postpartum, n=443) with body condition scores from 2.0 to 3.5 (5-point scale) on three farms were all given a synchronizing protocol (PEPE). At the start (designated Day 0), cows were given an intravaginal device (1.0g of progesterone) and 2.5mg of estradiol benzoate (EB) im. On Day 8, the device was removed and cows were given PGF_2α (150μg of d-cloprostenol im), followed in 24h by 1.0mg EB im, and 30–36h thereafter, fixed-time AI. The design was a 2×2 factorial; main effects were TCR (54–60h; from device removal to FTAI) and eCG treatment (300IU im, concurrent with PGF_2α). Transrectal ultrasonography was done on Days −10 and 0 to detect anestrus (absence of a CL at both examinations) and ∼30d after FTAI (pregnancy diagnosis). Data were analyzed by logistic regression. The following variables did not significantly affect pregnancy rates: farm, postpartum interval, cyclicity, inseminators, and semen (sire). Overall, 77% of the cows were deemed anestrus. Pregnancy rates were similar (P>0.05) among treatment groups: Control (54/108=50.0%), TCR (44/106=41.5%), eCG (63/116=54.3%), and TCR+eCG (49/113=43.4%). Pregnancy rate was higher in multiparous than primiparous cows (186/360, 51.7% vs. 24/83, 28.9%, P<0.01), but was not significantly affected by cyclicity status or body condition score. In conclusion, temporary calf removal, eCG, or both, did not significantly increase pregnancy rate to timed-insemination in a progesterone-based synchronization protocol in postpartum Nellore cows with acceptable body condition.

Keywords: Fixed-time artificial insemination, Progesterone, Bovine, eCG, Temporary calf removal