A Five-day Progesterone plus eCG-based Fixed-time AI Protocol Improves Fertility over Spontaneous Estrus in High-producing Dairy Cows under Heat Stress.

This study compared the efficiency of a five-day or standard (nine-day) progesterone-based 4 regimen combined with equine chorionic gonadotrophin (eCG) in a fixed-time AI (FTAI) 5 protocol for dairy cows. The data examined were derived from 3577 inseminations conducted in 6 three dairy herds. Animals with no estrus signs detected over 21 days were randomly assigned 7 to a PRID-9 or PRID-5 group. Cows in each group received a progesterone intravaginal device 8 (PRID) for 9 or 5 days, respectively, PGF2α and eCG on PRID removal, and GnRH 48 hours 9 later. Fixed-time AI was performed 12 hours after the GnRH dose. Cows artificially 10 inseminated following spontaneous estrus during the study period were considered as controls. 11 Based on the odds ratio, the likelihoods of animals in PRID-9 in the warm (conception 12 rate [CR] of 22.3%) and cool (32% CR) periods, and control animals in the warm period 13 (26.6% CR) becoming pregnant were reduced (by factors of 0.6, 0.3 and 0.4, 14 respectively) compared with the control animals in the cool period (CR of 43.7%). The 15 risk of a twin pregnancy was higher (51.4%) for cystic PRID-9 cows (by a factor of 3.6) 16 and lower (9.9%) for cyclic PRID-5 animals (by a factor of 0.4) compared with the 17 PRID-9 cyclic cows. These findings indicate that the proposed protocol achieves similar 18 results during the cool or warm season to those obtained when AI is conducted at spontaneous 19 estrus during the cool season. In addition, PRID-5 reduced twin pregnancy compared with 20 PRID-9.