Influence of feeding regime on timing of parturition in beef cattle and the relationship of vaginal temperature to parturition

The timing of parturition was recorded for a total of 56 beef cattle (Japanese Black x Holstein Friesian) on different dietary treatments. The rate of calving during daylight hours in cows night-fed (18.00 hours) with a roughage diet was significantly higher than that in cows night-fed with a high concentrate diet (79.2% vs 38.5%, P < 0.05). Subsequently, the vaginal temperature (VT) of these cows was analyzed using a cosinor method. When the feeding schedule was changed from twice daily (08.30 and 15.30 hours) to night feeding, the periodicity, the acrophase and the bathyphase, which were the parameters of the cosine curve, were unstable from the first day of night feeding until after day 6 (P < 0.05). Prior to parturition, the midline-estimating statistic of rhythm (MESOR) and the amplitude for the cows that were fed a high-roughage diet at night and that calved at night-time were lower and larger, respectively, than that for the other treatments (P < 0.01). Based on these results, the time of parturition in most of the beef cows was influenced by feeding time and diet composition. Those cows that calved at night-time in spite of night feeding had lower vaginal temperatures.