| Abstract: | Thoroughbred horses are seasonal mating animals, raised in northern regions or countries.Foals born yearly in spring generally show a typical seasonal compensatory growth pattern,in which their growth rate declines in the first winter and increases in the next spring.In this study, a new empirical adjustment approach is proposed to adjust for thiscompensatory growth when growth curve equations are estimated, by using 1,633 male bodyweights of Thoroughbreds as an illustrating example. Based on general Richards growthcurve equation, a new growth curve equation was developed and fit to the weight-age data.The new growth curve equation had a sigmoid sub-function that can adjust the compensatorygrowth, combined with the Richards biological parameter responsible for the maturity ofanimals. The unknown parameters included in the equations were estimated by SAS NLMIXEDprocedure. The goodness of fit was examined by using Akaike’s Information Criterion (AIC).The AIC values decreased from 13,053 (general Richards equation) to 12,794 (the newlydeveloped equation), indicating the better fit of the new equation to the weight-age data.The shape of the growth curve was improved during the period of compensatory growth. Theproposed method is one of the useful approaches for adjusting seasonal compensatory growthin growth curve estimations for Thoroughbreds, and for their management during thecompensatory period. Based on this approach, the optimal growth curve equations can beestimated also for female body weight of Thoroughbreds or other growth traits affected byseasonal compensatory growth. |
