PSXIV-13 - Evaluation of on-animal sensors for monitoring diurnal physical activity of beef bulls during the breeding season

Abstract: Applications of on-animal sensors (OAS), commonly used to monitor behavioral patterns in livestock, remain largely undeveloped for extensively managed beef bulls. Thus, the objective of this study was to characterize and compare two OAS types for monitoring bull activity during the breeding season. Angus and Angus crossbred beef bulls (n=50) aged 1-8 years, from six cow-calf operations in Ohio were placed into multi-sire breeding groups (n=19) with a bull-to-female ratio of 1:25 (range 1:16-1:31). Bulls were placed with a female group from day 10 (range day 5-12) until day 60 after fixed-time artificial insemination. Before turnout, each bull was subjected to a breeding soundness examination and fitted with a collar-mounted GPS and an ear tag-mounted triaxial accelerometer (AX3). Raw GPS and AX3 activity measurements, namely speed (m/s) and motion intensity (g), were converted to standardized Z-scores and summarized to an hourly resolution by computing the median hourly activity over a 24-hour cycle at early (day 13-28) and late (day 34-49) stages of the breeding season. Linear mixed models were fitted to standardized activity measurements (expressed in log scale) to assess the dynamic effect of OAS type throughout the day at early and late stages of the breeding season. Size of the breeding group (males and females), bull age, scrotal circumference, and body condition score were evaluated as potential explanatory covariates using stepwise selection. Diurnal activity curves followed a pattern of relative inactivity overnight from hours 21 to 5 and relative activity during daylight from hours 6 to 20. For both OAS, mean activity early in the breeding season was ~47% greater (P < 0.01) than late. At both breeding season stages, mean activity of bulls differed between OAS types (P < 0.01) at hours 2, 3, 4, 5, and 6 by at least 38%, with greater activity from GPS than AX3 (P < 0.05 in all cases). Conversely, at hours 13, 14, and 16, activity derived from AX3 was greater than from GPS by at least 2.5-fold (14: P < 0.01; 13 and 16: P < 0.1). There was no evidence (P > 0.1) for differences between bull activity derived from GPS or AX3 during the remaining overnight (21-1) and daytime (7-12, 15, and 17-20) hours. In conclusion, this study provides evidence that simultaneous assessment of bull activity using independent OAS, differed between technologies throughout a 24-h day. Additionally, over the course of the breeding season, both OAS indicated a decline in activity. Bull breeding activities are expected to be less frequent as the breeding season progresses; thus, these may explain the observed differences between stages of the breeding season. Further exploration of benchmarks for bull activity may yield useful tools for the identification of health and reproductive-related behaviors.