The aim of this study was to analyze the effect of sex, season and year of birth on growth rate of biometric measurements and body weight gain of Thoroughbred foals during first six months of life. 103 Thoroughbred foals (53 colts and 50 fillies) from Golejewko Stud born between 2006 and 2008, were used in this study. Thoroughbred foals born in winter months were characterized by significantly higher (P≤0.01) growth rate of height at withers, cannon circumference and body weight gain compared to foals born in spring months. The effect of year of birth on growth rate of height at withers was significant (P≤0.01), but differential and it was difficult to show a clear dependence. No significant effect of sex was observed on studied parameters except for body weight gain between 4 and 6 months of life. پرونده مقاله