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Effect of Short-Term Fasting and Refeeding on Weight and Blood Components of Steers Grazing Wheat Pasture^{1 ,2,}

U.S. Department of Agriculture, El Reno, OK 73036 , College Station, TX 77840 and Agricultural Experimental Station, Stillwater 74074

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.

¹ This research was conducted in cooperation with the Oklahoma Agricultural Experimental Station. Published with the approval of the Director as Journal Article No. 3173.

² The authors wish to express their appreciation to W. G. Jackson, R. E. Osburn, K. W. Williams, H. J. Muncrief, D. L. Ferrel and R. S. George for technical assistance.

³ Research Animal Scientist, U.S.D.A., A.R.S., Southwestern Livestock and Forage Research Station, El Reno, OK.

⁴ Animal Scientist, Oklahoma A.E.S., Stillwater.

⁵ Research Chemist, U.S.D.A., A.R.S. Veterinary Entomology and Toxicology Laboratory, CoUege Station, TX.