Dietary protein levels and the responses of broilers to single or repeatedcycles of fasting and refeeding

The present study was designed to study short-term responses accompanying e ither chronic or acute fasting-refeeding cycles. Seven-day old Shaver broil ers were fed diets containing either 120 or 300 g crude protein on either f ree choice basis or on 7 cycles consisting of 1 day of fasting followed by 2 days of feeding. In addition, birds fed free choice were subjected to the above regimen, but only for one cycle. Birds were bled and killed on day 1 , 2 & 3 of the final cycle for each of these experiments. Measurements take n at these intervals included in vitro lipogenesis (IVL), growth and feed c onsumption, hepatic enzyme activities and plasma triiodothyronine (T-3), an d thyroxine (T-4) Birds fed the lower level of crude protein free choice fr om 7 to 28 d ate less, were smaller and Less efficient in growth. De novo l ipogenesis and plasma T-3 were greater and T-4 was less in birds fed the lo wer protein diet. Birds subjected to repeated fasting-refeeding cycles exhi bited striking changes on each day of the cycle. The lowest rate of IVL was noted following a 1 day fast and the greatest after 2 day of refeeding. Th is pattern was noted in birds fed diets containing either 120 or 300 g crud e protein/kg although the responses were exaggerated in birds fed the lower level of protein. Chickens fed a low-protein diet in conjunction with a si ngle fasting-refeeding cycle exhibited responses that were similar to chron ic fasting-refeeding. The magnitudes of fasting-refeeding responses were ma gnified by repeated cycles of fasting-refeeding. Feeding a high level of pr otein modified some of the effects of a fasting-refeeding cycle. Published by Elsevier Science Inc.