Modeling the Growth of Thoroughbred Horses: The Relationship of Birth Height, Gestation Time, and Wither Height at Maturity

Abstract

This article presents an analysis examining the wither height growth curves of 33 Thoroughbred horses from birth to maturity. The growth curve of each animal was analyzed, and the mature height was determined. Having established each animal‘s mature height, the growth curves were then normalized using the individual mature height and gestation length. A birth ratio (B rh ) was established using the length of gestation divided by the fraction of maturity at birth (F bh ), and this value was found to be nearly identical for all horses in the study, indicating that the growth of each horse was very similar in normalized time. A relationship was developed predicting F bh as a function of birth height, gestation time, and the animal‘s sex, and a procedure is presented to estimate an animal‘s mature height based on F bh from the developed expression. The estimates of mature size were reasonable in most instances, and comparisons are shown indicating the efficacy of the predicted values compared to the values of mature wither height found from the growth curve regressions.