Extended Abstract
Introduction and Objective: Biometric measures of some body dimensions can be used as indicator of a particular breed. Among these characteristics, the horse's head and neck regions dimensions are of particular importance. These characteristics, in addition to showing differences among breeds of the horses, may also affect the performance and beauty of the animal. The long head and neck in horses makes the animal more flexible and increases the performance. Rearing conditions, age, sex and nutrition of the horses are important factors for body dimension traits.
Material and Methods: This study was conducted to investigate the effect of some environmental factors on biometric traits of the head and neck of Thoroughbred horses in Golestan province. For this purpose, the head and neck regions dimensions of 105 randomly selected Thoroughbred horses were measured.  The studied horses included 66 stallions and 39 mares ranging from 2 to 4 years of age. The number of horses in Gonbad Kavous, Aq Qala and Bandar Turkmen counties were 61, 24 and 20, respectively. According to the San Giacomo Standard and by using a tape meter, 13 biometric dimensions of the horses head and neck regions, including Head Length (HL), Ear Length (EL), Eye to Eye Width (EEW), Ear to Eye Length (EED), Eye to Jaw Length (EJL), Eye to Mouth Length (EML), Jaw Width (JW), Muzzle Circumference (MC), Head Neck Circumference (HNC), Neck Midpoint Circumference (NMC), Neck Body Circumference (NBC), Upper Neck Length (UNL) and Neck Down Length (NDL) were measured. Descriptive statistics, analysis of variance and comparison of least squares means (LSM), were obtained using Means procedure, General Linear Models (GLM) and Tukey-Kramer Test at a significant level of 5% by SAS statistical software, respectively.
Results: The results indicated that HL, EEW, MC, HNC, NBC and UNL traits were lower dispersion and coefficient of variations compared to other traits.The highest and the lowest coefficients of variation were estimated for JW (14.68%) and HL (4.29%), respectively. Analysis of variance showed that the effect of age on EEL (p<0.05) and NBC (p<0.01), sex on EEW (p<0.05), JW (p<0.01), MC (p<0.01), HNC (p<0.01), NMC (p<0.01) and NBC (p<0.01) and rearing area on HL (p<0.01), EEW (p<0.05), JW (p<0.05), MC (p<0.05), HNC (p<0.01), NMC (p<0.01), NBC (p<0.01) and UNL (p<0.01) traits were significant.
Conclusion: The results of this study showed that, the biometric dimensions of the head and neck regions of Thoroughbred horses were higher than those for other Iranian horses and environmental factors such as age, sex and rearing area had significant effects on these traits. The results of this study can be used for comparing, selecting and breeding of Thoroughbred horses of Golestan province.