A GROWTH STUDY OF BEEF CATTLE

Four growth equations (Richards, Brody, Von Bertalanffy and Logistic) were fitted to data from two breed groups of female beef cattle, purebred Hereford (HE) and synthetic of Charolais, Angus and Galloway (SY), which were maintained at the University of Alberta beef breeding research ranch at Kinsella, Alberta. All functions fitted three common parameters (an asymptote, an integration constant and a maturing rate parameter). Two functions (Von Bertalanffy and Logistic) had fixed inflection points while the Richards function fitted the inflection point as a fourth parameter. The Brody function had no inflection point. Based on the R 2 , mean prediction errors (MPE) and residual variances, the Richards function, with a variable inflection point, provided the best overall and the most consistent fit to both sets of data, followed by the Brody function with no inflection point. The Richards was the only function that could predict birth weight with any degree of accuracy. The Logistic and Von Bertalanffy functions, with fixed inflection points, provided poor estimates of actual weights at each end of the growth curve, overestimating birth weight and converging too early leading to underestimation of adult weight or the asymptote. Intermediate weights were reasonably well estimated by these functions. The HE group showed a 28% greater maturing rate compared with the SY based on the Richards function.