Influence of energy balance and body condition on estrus and estrous cycles in Holstein heifers.

The objective was to determine effects of energy balance and body condition on estrous behavior and estrous cycles in Holstein heifers. Before the experiment heifers were fed so body condition remained moderate or they became fat. During the 2 x 2 factorial experiment, moderate and fat heifers were in positive or negative energy balance. Heifers were fed individually twice daily, and energy balance was calculated daily. Heifers were observed for 30 min every 3 h, and all standing and mounting events were recorded for three consecutive estrous cycles. When progesterone in serum was less than 1 ng/ml, standing and mounting activity were profiled. Area, peak, and duration of activity profiles were examined among groups of heifers. Negative energy balance or fat body condition did not reduce peak or duration of estrous behavior and thus did not reduce detectability of estrus. Onset of diestrus was delayed in heifers that were fat and in negative energy balance relative to other heifers. We suggest that fat body condition, coincident with negative energy balance, may reduce accuracy of timing artificial insemination relative to ovulation and may consequently reduce fertility in cattle.