Reproductive strategies for dairy heifers based on 5d-cosynch with or without an intravaginal progesterone device and observed estrus

Abstract

The objective of this randomized, controlled study was to evaluate the reproductive and economic performance of dairy Holstein heifers managed for first to third artificial inseminations (AIs) with or without an intravaginal progesterone device (IPD) under different temperature-humidity indexes (THI) and combined with AI after observed estrus. A total of 503 heifers from one rearing commercial farm were randomly assigned for first AI to the 5d Co-synch 72 h protocol (5dCO; n=261) or to the 5d Co-synch protocol plus IPD (5dCOP4; n=242). In a subset of heifers (n = 193) we determined progesterone (p4) and performed an ovarian ultrasound scanner on Days 0, 5, 8 and 15. Animals were considered to be synchronized on Day 5 if p4 > 1 ng/mL and a corpus luteum present; synchronized on Day 8 if p4 < 1 ng/mL, luteolysis and a follicle > 8 mm diameter was observed; and synchronized on Day 15 if p4 > 1 ng/mL and ovulation occurred, defined as the presence of a CL in the ovary where a follicle had been detected on Day 8. Pregnancy diagnosis was performed by ultrasound scanner on Days 28-35 after AI. The diagnosis confirmation was done by ultrasound on Days 50-56 and again on Days 100-113 after AI. Non-pregnant heifers (n=205) were resynchronized with the same protocol for second fixed-time AI (FTAI) and 104 for third FTAI. Pregnancy per AI (P/AI) and pregnancy loss after each AI were calculated. Reproductive costs were calculated at the individual level, based on costs for pregnancy and cost for the open days. Estrus observation was performed by visual inspection for 20 min periods, twice a day and heifers observed in estrus inseminated (OEAI). Observed in estrus inseminated heifers were 10.5% at first, 26.8% at second and 24.0% at third AI (P >0.05). The global P/AI after first AI was 58.6%; the P/AI after FTAI, 58.0%; and the P/AI after first OEAIs, 64.2%. Pregnancy per AI values were better in the IPD group [55.2% for 5dCO vs. 62.4% for 5dCOP4; odds ratio (OR) 0.35, 95% confidence interval (CI) 0.18-0.70; P=0.003], and a significant effect of the temperature humidity index (THI) on P/AI was observed (P = 0.03). The protocol 5dCOP4 led to a significantly better synchronization rate (85.7% vs. 40.0% for 5dCO; P = 0.01) and a numerically higher P/AI (74.5% vs. 49.0% for 5dCO; P = 0.24) when THI values were ≥ 70. During the cold season, there were no differences between the experimental groups for the synchronization rate (P = 0.9) nor for the P/AI (P = 0.6). The P/AI was 52.2% after the second AI and 60.6% after the third AI. Inseminations per pregnancy and open days did not diffe significantly across experimental groups. However, reproduction costs per heifer were 130.8 ± 116.1 and 152.3 ± 129.5€ for 5dCO and 5dCOP4 groups, respectively, for the whole study (P = 0.051) and the average cost per AI was 58.23 ± 27.9 € for 5dCO and 76.3 ± 36.2 € for 5dCOP4 (P < 0.0001). During the cold season, protocols were associated with similar costs to the whole study, but they differed notably during the hot season (194.3 ± 137.6 vs. 177.3 ± 134.2 for 5dCO and 5dCOP4, respectively; P=0.49), reflecting the better reproductive performance with an IPD during the summer (P = 0.003). Advisors and farmers need to consider farm conditions and char- acteristics (herd management, staff training, and seasonality, among others) to achieve the best economic and reproductive performance in the dairy herds, when implementing hormonal synchronization protocols. Thus, cost-effectiveness depends on seasonality when implementing reproductive strategies with 5 d Co-synch 72h and combined OEAI at a rearing farm. With high THI-values, the inclusion of IPD in hormonal protocols in heifers is recommended, while it is not required during the cool season.