Automated and visual measurements of estrous behavior and their sources of variation in Holstein heifers. II: Standing and lying patterns

Lying (LY) and standing (ST) behavior of Holstein heifers (n = 57) was studied from Day -7 to Day +2 relative to estrus (Day 0) using leg-mounted accelerometers. A total of 269 estrus episodes were studied. The objectives were to quantify the effects of estrus on ST and LY patterns, identify sources of variation, and provide insight into new approaches for the use of sensors in estrus detection. The sensors were used to obtain ST bout frequency (bouts per day), total daily ST time, and mean bout duration and duration of the longest bout for ST and LY on a daily basis. Estrus episodes were identified using walking activity peaks and validated by ovarian ultrasonography. Repeated-measures ANOVA was used to analyze the effects of estrus order (pubertal vs. second and greater), season, time of estrus onset, category of baseline walking activity, and number of heifers simultaneously in estrus on ST and LY variables. Overall, ST bout frequency was lower, whereas mean ST bout duration, duration of the longest ST bout, and total daily ST time were longer on Day 0 (P < 0.05). The longest ST bout increased from 232 ± 5 minutes on Day -7 to 488 ± 16 minutes on Day 0 (P < 0.05), and on Day 0, it started within -2 to 4 hours of time of estrus onset. Measurements of ST bouts varied the most on Day 0 (coefficient of variation = 21.5%-52.8%). The pubertal estrus was characterized by smaller increase in mean ST bout duration, longest ST bout duration, and total daily ST time (P < 0.05) compared to the second and greater episodes. Second and greater episodes had greater longest LY bout on Day +1, but on Day 0 it was not different from other nonestrus days (P < 0.01). The longest ST bout on Day 0 was longer for heifers with high baseline walking activity and for episodes occurring during the cold season (P < 0.05). The effect of estrus on ST variables for morning-onset episodes was observed only on Day 0. Episodes with afternoon and night onset showed the effect of estrus spread over Days -1 and 0, resulting in a smaller change between Day -7 and Day 0. The number of heifers simultaneously in estrus did not affect the studied variables (P > 0.05). Measurements of ST and LY changed during estrus and were correlated to walking activity. The large increase in duration of the longest ST bout and its occurrence in proximity of estrus onset suggest potential for automation. Incorporating measurements of ST and LY corrected for sources of variation could improve estrus detection systems.