Comparison of Parameters Associated with Molt Induced by Fasting, Zinc, and Low Dietary Sodium in Caged Layers

Abstract

Three trials were conducted to compare the physiological effects of fasting, the effects of a low level of dietary sodium, and a high dietary level of zinc as induced molting agents for commercial strains of laying hens. Photoperiod modifications were included in the third trial. The Single Comb White Leghorn (SCWL) laying hens were induced to molt by fasting (FAST) to a body weight loss of 30 to 34% by administration of a diet containing 500 mg/kg sodium (Lo Na) for 42 days or by administration of a diet containing 20,000 mg/kg added zinc (Hi Zn) for 7 (Trial 1) or 10 (Trials 2 and 3) days. Water was available ad libitum and photoperiod was maintained at 17 hr except in Trial 3 in which half of the hens received a photoperiod of 8 hr during the first 42 days of the experiment. Both the FAST and Hi Zn treatments produced a cessation of egg production within five days after the initiation of treatment. Egg production was reduced but did not cease in the Lo Na treatment. Body weights, liver, ovary, oviduct, and right adrenal weights were determined at regular intervals.The FAST treatment produced the greatest degree of body and organ weight loss, while the Lo Na treatment produced the least. The Hi Zn treatment produced intermediate results.Right adrenal weight exhibited no consistent change. The 8-hr photoperiod tended to reduce body weight and significantly reduced the weights of liver, ovary, and oviduct regardless of dietary treatment.