Abstract
The objective was to compare two protocols for synchronizing ovulation in lactating Holstein cows submitted to timed AI (TAI) or timed ET (TET). Within each farm (n = 8), cows (n = 883; mean ± SEM 166.24 ± 3.27 d postpartum, yielding 36.8 ± 0.34 kg of milk/d) were randomly assigned to receive either: 1) an intravaginal progesterone insert (CIDR®) with 1.9 g of progesterone + GnRH on Day -10, CIDR® withdrawal + PGF2α on Day -3, and 1 mg estradiol cypionate on Day -2 (treatment GP-P-E; nTAI = 180; nTET = 260); or 2) a CIDR® insert + 2 mg estradiol benzoate on Day -10, PGF2α on Day -3, CIDR® withdrawal + 1 mg estradiol cypionate on Day -2 (treatment EP-P-E; nTAI = 174; nTET = 269). Cows were subsequently randomly assigned to receive either TAI on Day 0 or TET on Day 7. Serum progesterone concentration on Day -3 was greater in GP-P-E than in EP-P-E (2.89 ± 0.15 vs 2.29 ± 0.15 ng/mL; P < 0.01), with no significant effect of group on serum progesterone on Day 7. Compared to cows submitted to TAI, those submitted to TET had greater pregnancy rates on Day 28 (44.0% [233/529] vs 29.7% [105/354]; P < 0.001) and on Day 60 (37.6% [199/529] vs 26.5 [94/354]; P < 0.001). However, there were no effects of treatments (GP-P-E vs EP-P-E; P > 0.10) on synchronization (87.0% [383/440] vs 85.3% [378/443]), conception (TAI: 35.3% [55/156] vs 33.8% [50/148]; TET: 50.7% [115/227] vs 51.3% [118/230]) and pregnancy rates on Days 28 (TAI: 30.5% [55/180] vs 28.7% [50/174]; TET: 44.2% [115/260] vs 43.9% [118/269]) and 60 (TAI: 27.2% [49/80] vs 25.9% [45/174]; TET: 38.8% [101/260] vs 36.4% [98/269]). In conclusion, GP-P-E increased serum progesterone concentrations on Day -3, but rates of synchronization, conception, and pregnancy were not significantly different between cows submitted to GP-P-E and EP-P-E protocols, regardless of whether they were inseminated or received an embryo.
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