DIURNAL PATTERNS OF ESTROUS BEHAVIOR OF DAIRY COWS HOUSED IN A FREE STALL

Sixteen primiparous and fifteen multiparous cows housed in a free-stall area with slatted floor alley were observed continuously for 100 d postpartum using a time-lapse videorecorder. Low intensity (< than 3 lx) red lights were used for nocturnal illumination. Natural daylight from an existing window and incandescent lamps provided daytime illumination (12–52 lx). The analyses focused on the periestrous period beginning 2 d prior to and ending 2 d after estrus. Onset of true estrus was most frequent between 1200 and 1800 h in the primiparous group (35%) and between 0600 and 1200 h in the multiparous group (37%). A nadir of true estrus onset (15%) occurred between 1800 and 2400 h in both groups. The predominant hours of estrual activities occurred during daylight, between 1500 and 1800 h in the primiparous group and between 0900 and 1100 h in the multiparous group. In general, the daily distribution of estrous activities had a quadratic shape and these shapes or patterns of estrous activities were remarkably consistent among cows and estruses. Among the monitored estrual activities, mounting, sniffing and chin pressed in the primiparous group, and chin pressing, chin pressed, mounting, mounted and sniffed in the multiparous group, were found to best discriminate the cows' behaviors on estrous day with their behaviors on the 2 days pre- and postestrus. Key words: Reproductive behavior, sexual behavior, estrous behavior, cow behavior, cow (dairy)