The Effects of Estrus on Dry Matter Intake and Feeding Behavior in Beef Heifers

Crossbred beef heifers (n = 73) were used to evaluate the impacts of estrus on feed intake and feeding behavior in the days before, during, and after standing estrus. Our hypothesis was that estrus activity would reduce DMI and alter feeding behavior. Heifers were acclimated to the Insentec feed system and were assigned to pen by frame score, a calculation of age and hip height, with treatments being small to moderate frame (SMD; frame score less than or equal to 5.50; n = 44) and moderate to large frame (MLG; frame score of 5.50 or greater; n = 29). On d one of the study, heifers were fitted with Accubreed electronic pressure sensing heat detection devices to monitor estrus behavior. Heifers were fed a total mixed ration containing 79% grass hay, 17% corn silage, and 4% vitamin and mineral premix for ad libitum intake for 107 days, during which time feed intake and behavior, and date, time, and duration of individual mount events were monitored. Upon completion of the study, feed intake data were aligned with estrus data for each of the 7 d before and after the first mount of an estrus. Data were analyzed using the GLM procedure of SAS for main effects of treatment, day relative to estrus, and treatment × day interactions. We observed 266 estrus events, with a mean duration of 8.26 ± 0.38 h and 12.7 ± 0.77 mounts lasting 4.06 ± 0.09 s, for a total time standing of 49.1± 2.97 s per estrus. No treatment × day interactions were detected. Heifers in the MLG group had greater (P < 0.001) DMI, made more visits to troughs, spent more time eating, and had greater number of meals over all feeding events compared with SMD heifers. In contrast, SMD heifers spent more time per visit and meal, and had greater DMI per visit and per meal compared with MLG heifers (P < 0.001). On the day of estrus, heifers had reduced (P < 0.001) DMI, visits to troughs, number of meals, and time spent eating compared with each of the 7 d before and the 7 d after estrus. We observed that the change in feed intake and behavior relative to estrus is rapid, and these variables returned to baseline levels within one day following standing heat.