Physiological relationships with production measures in White Leghorns subjected to restricted feeding from 18 weeks of age

Abstract

The relationships between 22-42 week production measurements (egg number, egg weight, feed conversion efficiency, carcass fat, shell thickness and body weight) and a number of physiological measures (metabolic rate, water turnover, thyroxine secretion rate and plasma thyroxine concentration) were examined in purebred and strain-cross White Leghorn hens. Feed intakes were restricted to 80, 90 or 100 g 24h-1 and comparisons made with birds allowed free access to feed (average 127 g 24h-1). Restricted feeding significantly depressed all production measures except egg weight and shell thickness, and also reduced metabolic rate but elevated the plasma thyroxine concentration. Strain-cross hens laid more and heavier eggs, and showed a better feed conversion efficiency than purebreds in association with reduced metabolic rates, thyroxine secretion rates and plasma thyroxine concentrations. Water turnover was the only physiological measure to be consistently related to production measurements, and in the case of egg number, egg weight and shell thickness, different relationships were demonstrated in restricted compared with fully fed birds.