Selection for Body Weight at Eight Weeks of Age: 15. Feed Passage and Intestinal Size of Normal and Dwarf Chicks

Abstract

Comparisons were made of feed passage rates and size of the gastrointestinal tract components among populations of chickens exhibiting wide differences in growth rate. The populations consisted of White Plymouth Rock stocks selected bidirectionally for high and low juvenile body weight. Comparisons included males heterozygous for the sex-linked gene for dwarfism, as well as normal and dwarf males and females.The indigestible marker, ferric oxide, appeared earlier and disappeared later in the excreta of males from the low-weight line than in those from the high-weight line. Results with female chicks were similar, except that line differences in the time to the first appearance in the excreta were not significant. There were no significant differences in feed passage rates due to the dwarf gene.The weights of the crop, gizzard, duodenum, and the total gastrointestinal tract were, when expressed as a percentage of body weight, significantly heavier for male chicks from the low-weight than for those from the high-weight line. Duodenum weights of female chicks from the low-weight line were also significantly larger than those from the high-weight line. Effects of the dwarfing gene on various components of the gastrointestinal tract, when expressed as percentage weights, were not significant with one exception. Dwarf females from the high-weight line had lower duodenum weights than normals while the reverse was true in the low weight line. In general, the proportionately larger intestinal weights appeared to correspond with a slower clearance of feed through the gastrointestinal tract and may be indicative of altered digestive or absorptive functions resulting from selection for growth.