Growth curves from birth to weaning for Thoroughbred foals raised on pasture.

The research study describes the mathematical modelling of the growth of Thoroughbred foals up to the point of weaning on different types of pasture in New Zealand. The findings suggest that birthweight is a primary determinant of growth, and also indicates that foals reared on pasture may grow as well as those in grain-based systems.

Study Methodology

• The study used data from 218 Thoroughbred foals (including 120 fillies and 98 colts) born over six years. These foals were raised on four different types of pastures.
• The researchers collected the foals’ liveweights twice a month, starting at birth up until the weaning stage, which is within 107 to 217 days from birth. A total of 3,200 data points were obtained.
• To ascertain the relationship between the age of foals and their liveweight, they performed a non-linearity test.
• They determined the goodness of fit of their data by testing five non-linear regression equations.

Study Results

• It was established that both foal genders had comparable birthweight, weaning ages, weaning weights, and average daily weight gain from birth to weaning.
• Weaning age accounted for nearly half of the variation in weaning weights and around an eleventh of the variation in daily weight gain from birth to weaning. After adjustments were made for weaning age, birthweight was found to explain 16% and 6% of the variation in weaning weight and daily weight gain, respectively.
• The best-fit equation demonstrating the relationship between age and liveweight was the polynomial equation, as determined by several criteria such as the Akaike’s information criteria, residual variance, residual standard deviation, and the coefficient of determination.

Conclusions

• The researchers concluded that the existing data align with growth information from the Northern Hemisphere, verifying that foals brought up on pasture can develop just as well as foals raised in grain-based systems.
• Additionally, the study reinforces that birthweight is a logical setpoint for predicting growth until weaning, as opposed to using polynomial equations that, despite giving an exact mathematical illustration, do not adequately depict the biology of growth.