Comparison of nonlinear functions for describing the growth curve of three genotypes of dairy cattle

Abstract

The Richards (RCD), the Gompertz (GMP), the monomolecular (MON) and the logistic (LOG) functions were compared for describing the growth curve of 343 female dairy cattle for which 12–18 body-weight measures were available. The animals were divided into four groups, and each function was assigned to one of the groups. Analyses of variance of growth traits estimated by the four functions and of the residual mean squares (RMS) indicated that all differences between functions in estimated mature weight (A) were statistically significant (P < 0.01 to P < 0.0001) except for RCD vs. GMP (P < 0.27). Differences between functions in RMS were significant for RCD vs. LOG (P < 0.0026), MON vs. LOG (P < 0.0044) and GMP vs. LOG (P < 0.0584). RCD differed from all other functions in average lifetime growth rate (P < 0.1 to P < 0.0001) and from MON (P < 0.0004) and GMP (P < 0.0003) in average lifetime maturing rate. Analysis of residuals indicated that both GMP and LOG overestimated birth weight. MON overestimated mature weight, whereas LOG tended to underestimate this parameter. The Richards function was chosen to describe the actual growth curves of individual females of three different genotypes. Predictive equations for the three breed groups were derived. Key words: Dairy cattle, growth curves, nonlinear functions