Growth analysis of the domestic fowl: III. Effect of plane of nutrition on carcass composition of cockerels and egg yields of pullets

Abstract

1. 101 Rhode Island Red × Light Sussex chickens have been made to conform to four major changes in the shape of their growth curves from hatching to twenty-four weeks, by control of their plane of nutrition. The four treatments (HH), (LH), (HL) and (LL), allowed comparisons to be made between birds of the same age, but different weights. As the main concern has been to find the essential nature rather than the precise extent of the effects produced by different planes of nutrition, the treatment differences were made as extreme as possible without allowing the rations to become unbalanced. 2. Certain individual organs and tissues, the gonads, thyroid and thymus, and the combs and wattles have reacted differentially to the contrasted treatments when compared on a basis of equal body weight. All the organs, with the exception of the very early maturing eyes and heart, have reached significantly different weights on the basis of equal age. Those organs which have yielded treatment differences judged on both the basis of equal weight or equal age have all been late maturing. The results therefore indicate that the effect of treatment has been to restrict the development of the later maturing parts in the case of the low-plane birds, and to accelerate the development of these organs when the birds are reared on the high plane. The results are insensitive to any differential effects which may have been brought about in the early maturing organs, since the design of the experiment did not allow of the slaughtering of birds at equal weight but only at equal age. The means of Comparison of differences at equal weights was the less precise method of ascertaining whether the high- and low-plane regression lines of weight of part to total weight of bird differed significantly the one from the other.