Utilization of Feed in Fast- and Slow-Growing Lines of Chickens

Abstract

INTRODUCTION FOR several decades geneticists have selected animals for maximum body size and growth rate, but have paid little attention to the physiological changes which underlie, or are correlated with, the observed genetic advances. Since a knowledge of the mechanisms controlling growth is of both scientific and practical interest, development and investigation of experimental and commercial strains of animals selected in divergent directions for growth has begun at a number of stations. At the University of Massachusetts, fifteen generations of breeding have developed, from a single base population, two strains of White Plymouth Rock chickens having vastly different rates of growth. In the twelfth generation, the 8-week body weight of these “high” and “low” lines differed by a factor approaching three (Farrington, 1966). Previous investigation has explored the endocrinological differences which may be related to this drastic divergence in growth rate (Komiyama et al., 1965; Farrington, 1966; Farrington and Mellen,…