Growth Patterns of Angus, Hereford and Shorthorn Cattle. I. Comparison of Inbred a N D N O N I N B R E D Lines, Changes in Patterns over Time and Effects of Level of Inbreeding and Reproductive

Mature weight (A) and rate of maturing (K) were estimated for 283 Angus, 140 Hereford and 280 Shorthorn cows utilizing the asymptotic regression equation Yt=A(1-Be'Kt). The Yt was weight of the individual at age t; and B was an estimate related to early life weight changes and provided for a Yintercept (A-B). Each breed consisted of four inbred and two noninbred lines. Regression of estimated growth curve parameters on levels of inbreeding of the individuals and of their dams and effects of early reproductive performance (EREPRO) were studied as sources of variation in addition to line differences and trends in line values over years. Considered jointly with inbreeding of the dam and with EREPRO, inbreeding of the individual was negatively related (P<.01) to estimates of A in the three breeds and unrelated (P>.10) to estimates of K. Each 1% increase in inbreeding of the individual was associated with about 2 kg decrease in estimated mature weight. An increase in inbreeding of the dam of an individual was negatively related to estimates of K in Angus (P<.01) and Shorthorns (P<.05). Inbreeding of dams was positively related to estimates of A in the three breeds, but only in Shorthorns could the relationship be declared significant. Estimates of A were about