Influence of age and sex of growing broiler chicks and body weight of roosters on their endogenous and metabolic energy losses.

Two experiments were conducted to study the influence of age, sex, body weight, and strain of the bioassay bird on its 24-hr combined endogenous urinary and metabolic fecal energy (Yec) losses, expressed as kJ/100 g body weight per 24 hr. In the first experiment, one-day-old broiler chicks of mixed sexes were used and their Yec losses determined at 18, 32, 47, 62, 77, 92, and 107 days of age. In the second experiment, the Yec losses of four White Leghorn roosters were determined at 122 days of age only. Birds were fed a commercial broiler-starter diet through-out the experimental period. It was concluded that the sex of the broiler chick between 18- and 107-days of age does not affect the Yec losses, i.e., the energy the unfed bird loses daily per unit body weight in its voided excreta. However, the average Yec losses expressed (either per unit body weight or per unit body size, Wkg.75 were influenced by age. The Yec losses showed a progressive fall as broiler chicks progressed in age between 18 and 77 days of age and later were stabilized at a minimum between 77 and 107 days of age. As the observed decrease in the Yec losses with increases in age followed a similar trend to that reported in the literature for the basal metabolic rate (BMR) energy needs of the chick, it was tentatively concluded that the Yec losses of broiler chicks vary with age according to the BMR energy needs per unit body weight of the animal. The average Yec losses of White Leghorn roosters at 122 days of age was significantly higher than that of 107-day-old broiler pullets even though the average weight of the rooster was only 53% that of the pullets. It was tentatively concluded that variations existing in the Yec losses of adult birds of same or different strains and sex are mainly attributed to differences in their body composition and BMR energy needs. However, further research is needed in order to verify this conclusion.