Time of insemination relative to reaching activity threshold is associated with pregnancy risk when using sex-sorted semen for lactating Jersey cows.

The objective of this observational experiment was to determine the association between the interval from reaching activity threshold (AT) to artificial insemination (AI) with sex-sorted semen and the probability of pregnancy. Jersey cows (n = 678) from a commercial dairy herd were fitted with heat-rumination long-distance collars (SCR Ltd., Netanya, Israel) at approximately 42 ± 7 days postpartum. Cows were presynchronized with three injections of PGF2α given 14 days apart starting on Day 39 ± 3 postpartum. Cows in estrus, based on tail paint removal, after 50 ± 3 days postpartum were inseminated by one of three technicians with semen from one of six sires. Cows were examined for pregnancy at 31 ± 3 and 66 ± 3 days after insemination. Only cows inseminated in estrus and examined for pregnancy at 31 ± 3 days after AI were used in the experiment (n = 419). A subsample of cows (n = 35) were examined by ultrasound every 8 hours after reaching AT to estimate the interval from reaching AT and ovulation. The mean (± standard error of the mean) interval from reaching AT to AI was 16.9 ± 0.5 hours, whereas the interval from peak activity to AI was 9.8 ± 0.5 hours. The length of high activity among cows diagnosed in estrus was 17.3 ± 0.3 hours. The mean interval from reaching AT to ovulation was 25.7 ± 1.2 hours. There was a quadratic effect of the interval between reaching AT and AI on probabilities of pregnancy at 31 ± 3 (P = 0.07) and 66 ± 3 (P = 0.15) days after AI. Pregnancy per AI at 66 ± 3 days after AI was higher for cows inseminated between 23 and 41 hours after the onset of estrus (≤ 3 hours = 20.0%, 4-12 hours = 27.1%, 13-22 hours = 39.1%, 23-41 hours = 45.6%, and ≥ 42 = 40.0%). Insemination of lactating Jersey cows with sex-sorted semen closer to expected ovulation yielded the highest probability of pregnancy.