Influence of Age and Sex on the Utilization of Proximate Nutrients and Energy by Chickens

Abstract

Digestibility and retention of nutrients were determined on 5 groups of 15 male and 5 groups of 15 female New Hampshire chicks at two, 4, 7 and 11 weeks of age. At 26 weeks of age an additional experiment was carried out with the 5 groups of females after the number had been reduced to 10 pullets per group. Chromic oxide was used as an indicator of digestibility and a single diet, containing approximately 21% of protein, was fed throughout the entire investigation. Only insignificant differences between male and female chickens were found for the digestibility of organic substance, protein, fat, fiber and nitrogen-free extract. On the other hand, the differences in digestibility of these nutrients at various ages were in most instances significant. The pattern was similar for all nutrients: after a slight increase from two to 4 weeks of age the digestibility generally declined steadily. Only the variation of protein digestibility may be of some practical importance. For all other nutrients the differences between digestibility at various ages were too small to be important for the formulation of feeding standards. For metabolizable energy a slight increase from two to 4 weeks of age and a steady decrease from 4 to 11 or 26 weeks of age were found. It appeared probable that this variation was principally a reflection of differences in protein retention at various ages. With the exception of a slight increase from two to 4 weeks of age, the percentage of nitrogen retention steadily decreased with advancing age. The differences between percentage nitrogen utilization of males and females were insignificant. The quantity of protein retained per day increased gradually up to the age of 7 weeks and decreased thereafter, showing a variation similar to that of the gain in weight per day. On the basis of the experiments reported the following crude protein requirements were estimated: at two weeks 20%, at 4 weeks 21%, at 7 weeks 15%, at 11 weeks 12%, and at 26 weeks 11%. The percentage retention of crude ash declined rapidly after 4 weeks of age. At 11 weeks crude ash intake and crude ash excretion were nearly equal.