Holstein heifers (n=57) were monitored using accelerometers and video observations with the objective of better understanding the behavioral expression of estrus, the variation within and between the heifers, and the possible sources of variation. IceTags recorded walking activity from 7 to 13months of age. Activity peaks (n=282) were obtained from a rolling sum of steps within 24-hour periods and validated to be estrus by ovarian ultrasonography. Behavior around activity peak of one estrus for each of 12 heifers was described in detail from video recordings. Baseline behavior was monitored in a corresponding interval 1week before. Estrus and baseline total steps and steps per hour, estrus relative increase in activity, duration, and interval between episodes were analyzed by descriptive statistics and Spearman rank correlations. Effects of category of baseline walking activity, estrus order (pubertal vs. second and greater episodes), season, hour of estrus onset, and number of heifers simultaneously in estrus were evaluated with proc MIXED. Behavioral changes from baseline to estrus were evaluated by a signed-rank test. Estrus total steps varied greatly (4743±1740; range: 837-10,070), as well as the relative increase in activity (290±160%; range: 30%-1190%). Duration of estrus was 14±4hours, ranging from 4 to 26hours. The interval between episodes was the trait that varied the least. Pubertal estrus was shorter and had a smaller relative increase in activity than second and greater episodes (P<0.05). The number of steps during estrus was greater for heifers of high baseline activity (P<0.01). Estrus episodes occurring in the winter and starting between 4 PM and 3 AM had the greatest relative increase in activity (P<0.05). The number of heifers simultaneously in estrus did not influence estrus expression (P>0.05). The behaviors with greatest change from baseline to estrus were chin rest, sniff, back mount, crossover, accept chin rest, and follow, but variation was large. Overall, estrus was apparent in behavioral changes with large variation within and between the heifers. Estrus order, onset hour, season, and baseline walking activity are important factors affecting estrus activity. Therefore, estrus detection tools should account for potential sources of variation. The visual and automated measurements of estrus expression reported in this study reveal possibilities for improved on-farm estrus detection technologies and potential genetic selection for estrus expression.
|Early online date||25 Mar 2015|
|Publication status||Published - 2015|
- Individual variation
- Walking activity