On the Description of Equine Somatic Growth Using Nonlinear Functions.
Authors: Darmani Kuhi Hassan, Hossein-Zadeh Navid Ghavi, France James, López Secundino
Journal: Journal of equine veterinary science
Summary
# Editorial Summary: Modelling Equine Growth Curves Understanding how horses grow is fundamental to developing appropriate nutrition and management protocols throughout their development, yet selecting the correct mathematical model to describe this growth has received limited attention. Kuhi and colleagues compared five nonlinear growth functions—three with diminishing returns patterns (monomolecular and Michaelis-Menten) and two with sigmoidal (S-shaped) characteristics (Gompertz and Richards)—using published data from Quarter Horse males and Thoroughbred foals and fillies tracked from birth to maturity, applying robust regression analysis via the Marquardt-Levenberg algorithm and assessing model fit through adjusted coefficients of determination and root mean square error. Contrary to expectations, the diminishing returns models provided superior fit to the data, suggesting that equine growth follows a pattern of progressively slowing velocity rather than the biphasic acceleration-deceleration typical of sigmoid curves. This finding has practical implications for nutritionists and managers: growth trajectories are more linear in early life and flatten more gradually than S-curve models would predict, affecting how we time nutritional interventions, plan training loads, and monitor developmental soundness across different breeds and sexes. The research provides a quantitative framework for predicting when individual horses approach mature size in body weight and skeletal height—information that helps farriers, veterinarians and physiotherapists tailor interventions to genuinely age-appropriate developmental stages rather than relying on generalised growth timelines.
Read the full abstract on PubMed
Practical Takeaways
- •Use diminishing returns growth models rather than sigmoidal models when predicting or monitoring individual horse growth from birth to maturity
- •Understanding accurate growth curve mathematics can improve nutritional management and health interventions tailored to expected growth patterns at different ages
- •Growth predictions based on these models may help identify developmental abnormalities earlier in foals and young horses
Key Findings
- •Diminishing returns models (monomolecular and Michaelis-Menten) are more adequate than sigmoidal models for describing equine growth curves
- •Richards, Lopez and Gompertz equations suggest growth curves in horses are not sigmoidal despite their theoretical asymptotic properties
- •Growth modeling applies to quarter horse males and thoroughbred foals and fillies from birth to maturity using body weight, withers height, and body weight to withers height ratio as somatic traits