Effect of Short-Term Fasting and Refeeding on Weight and Blood Components of Steers Grazing Wheat Pasture2

Abstract

Three fasting-refeeding trials were conducted with steers grazing winter wheat pasture. Treatment groups were (1) no fast “control”, (2) 12-hr fast, (3) 24-hr fast, (4) 48-hr fast (fast periods in groups 2 through 4 began at 8:00 am), (5) no fast “control” and (6) 48-hr fast (fasting periods for group 6 began at 8:00 pm). Forage analysis indicated that the protein level exceeded 22% during all trials and that the forage was highly digestible. Cattle beginning a fast at 8:00 pm lost more weight (P<.05) than did comparable cattle begining an equal-time fast at 8:00 am. Groups 1, 2, 3 and 5 animals generally maintained a constant body weight during the fasting periods. Average weight losses during fasting periods were 14.7 kg for group 4 animals and 22.7 kg for group 6 animals. Weight recovery in both groups in the post-fast grazing period was steady, but only about two-thirds of the lost weight was recovered after 14 hr of renewed access to forage. Plasma ammonia levels were not significantly different (P>.05) either among groups or between trials. The overall average was 3.22 µg NH3-N/ml. Plasma urea nitrogen was reduced (P<.01) by fasting in groups 3, 4 and 6, but not in group 2. There was no effect of treatment or trial (P<.05) on total serum protein levels.