Association of estrous expression detected by an automated activity monitoring system within 40 days in milk and reproductive performance of lactating Holstein cows

摘要

The objective of this observational study was toevaluate the association of estrous expression within 40days in milk (DIM) using a neck-mounted automatedactivity monitor (Heatime Pro; SCR Engineers Ltd.)with reproductive performance in lactating Holsteincows. A total of 2,077 cows (614 primiparous cows and1,463 multiparous cows) from 5 commercial dairy farmswere included in the statistical analyses. Activity datafrom the first 7 d after calving were excluded. An estrusevent was defined as an activity change index ≥35 formore than 2 h. Cows were classified according to thenumber of estrus events from d 7 until d 40 postpartuminto 3 categories: (1) no estrus event (Estrus0); (2) oneestrus event (Estrus1), and (3) 2 or more estrus events(Estrus2). Generalized linear mixed models were usedto analyze continuous and categorical data. Sharedfrailty models were used for time to event data. Overall,52.7% of cows had no estrus event detected by anautomated activity monitor system from d 7 until d 40postpartum. Herd level prevalence of Estrus0 rangedfrom 37.5 to 58.4%. Estrous expression from d 7 untild 40 postpartum affected estrous duration and estrousintensity at first artificial insemination (AI). Cowsin Estrus0 had the shortest duration (13.2 ± 0.33 h)compared with cows in Estrus1 (13.8 ± 0.36 h) andEstrus2 (14.8 ± 0.41 h). Cows in Estrus2 had a longerestrous duration at first postpartum AI compared withcows in Estrus1. Among Estrus0 cows, 46.2% had anestrus event with high intensity at first postpartum AI.Among cows in Estrus1 and Estrus2, 50.8 and 53.8%had an estrus event with high intensity at first postpartumAI, respectively. There was a significant differencebetween Estrus2 and Estrus0 and a tendency betweenEstrus0 and Estrus1. There was no difference betweenEstrus1 and Estrus2. For Estrus0, Estrus1, and Estrus2cows, pregnancy per AI was 29.4, 30.9, and 37.8%, respectively.There was a significant difference betweenEstrus0 and Estrus2 and Estrus1 and Estrus2. Therewas no difference between Estrus0 and Estrus1. Estrousexpression from d 7 until d 40 postpartum affected timeto first AI and time to pregnancy. Compared with Estrus0cows, cows in Estrus1 [hazard risk (HR) = 1.74]and Estrus2 (HR = 1.77) had an increased hazard ofbeing inseminated within 100 DIM. There was no differencebetween Estrus1 and Estrus2. Median DIM tofirst AI were 70, 59, and 58 for cows in Estrus0, Estrus1,and Estrus2, respectively. Compared with Estrus0 cows,cows in Estrus1 (HR = 1.28) and Estrus2 (HR = 1.33)had an increased hazard of becoming pregnant within200 DIM. There was no difference between Estrus1 andEstrus2. Median DIM to pregnancy were 127, 112, and103 for Estrus0 cows, Estrus1 and Estrus2, respectively.In conclusion, cows with no estrous expression from 7to 40 DIM had reduced estrous expression at first AIand inferior reproductive performance compared withcows that displayed estrous activity.