Effects of progesterone supplementation on reproductive responses in dairy cows subjected to timed AI programs: a meta-analysis

Abstract Text: Objectives were to summarize the effects of progesterone supplementation during synchronization programs on pregnancy per AI (P/AI) and pregnancy loss in dairy cows thru a meta-analysis. A systematic search for peer-reviewed manuscripts using Pubmed and ScienceDirect databases (keywords: progesterone, dairy cow) yielded a total of 2,384 results. Only controlled clinical trials were included (k=16), in which lactating dairy cows were either assigned to receive a single intravaginal device containing progesterone or remained as untreated controls subjected to the same timed AI (TAI) protocol. Studies were classified upon whether cows received the first AI postpartum or subsequent AI (first, 2+, mixed), if presynchronization was performed, and if cows were observed for estrus and allowed to be inseminated before TAI. A subset of studies with cows classified based on presence of CL at the initiation of the TAI protocol (k=10) was used to assess the effects of progesterone supplementation according to CL status. First and second pregnancy diagnoses were performed on d 30 (27-150 d) and d 60 (41-150 d) after AI. Pregnancy loss was defined for cows that lost their pregnancies between d 30 and 60. Meta-analysis was conducted using the Metafor package for R. Study was considered random and moderator variables were included as fixed effects. Results were reported as adjusted relative risk (RR) and its 95% confidence interval. Pregnancy loss and P/AI were calculated from raw data. Overall, progesterone supplementation increased (P=0.003) P/AI on d 60 (RR=1.19; 95%CI=1.07-1.32; P/AI: 33.3 vs. 28.6%). Presynchronization of the estrous cycle and AI number did not impact the benefit from progesterone supplementation and accounted for 6.9 and 6.0% of the heterogeneity, respectively. Allowance for AI at detected estrus accounted for 47.4% of the heterogeneity and reduced (P=0.01) the benefit from progesterone supplementation compared to TAI only (RR=0.81; 95%CI=0.68-0.95; P/AI supplemented vs. control: estrus-AI or TAI = 32.6 vs. 30.2%, TAI = 34.5 vs. 25.9%). Progesterone supplementation tended to reduce (P=0.09) pregnancy loss (RR=0.82; 95%CI=0.66-1.02; pregnancy loss: 10.9 vs. 13.0%); all heterogeneity was explained by AI number as supplementation reduced pregnancy losses in cows receiving first postpartum AI (10.1 vs. 14.0%) but not subsequent AI (11.8 vs. 12.0%). Subgroup analyses depicted that the benefit of progesterone supplementation on P/AI at 60 d and pregnancy loss were not affected by CL status. In conclusion, progesterone supplementation improved fertility mainly in cows not detected in estrus during the TAI program.

Keywords:

Dairy cow, progesterone, meta-analysis