The body size and weight of 584 Banei draft racehorses at Obihiro Racing Stable in Hokkaido, Japan, was investigated. Almost all the animals (94.7%) were crossbreed heavy draft horses; there were a few Percheron and Percheron grade (4.8%) and a Belgian breed (0.5%). The ages of the animals ranged from 2 to 10 years. Males accounted for 80.3%, females for 17.5%, and 2.2% were castrated. The mean body measurements of 2-year-old Banei draft racehorses were significantly smaller than those of the 3-to 4-year-old or 5-to 10-year-old horses. Hip width, croup width, and rump length of females were greater than those of males. In contrast, males had greater chest width and cannon bone circumference than females. Significant relationships among almost all body measurements were observed. A high correlation was found between body weight and chest girth, croup width and body length. A principle component analysis were applied to investigate the effect of body conformation on racing performance in terms of earnings and the time on the performance test. Performance was significantly related to the principle components of general body size and weight of the horses. The cannon bone, body length, and rump length were suggested to have an effect on earnings per race in 2-year-old male horses. In terms of body size and conformation, the Banei draft racehorses, which are large in general size and well balanced, seemed to show high performance.

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We estimated the genetic parameters for body weight and ten measurements (height at withers, height at croup, body length, chest depth, chest width, hip width, croup width, rump length, chest girth, and cannon bone circumference) at different ages in Breton and Percheron horses. Data included 307 Breton and 324 Percheron horses born between 1999 and 2011 at the Tokachi Station, National Livestock Breeding Center, Japan. The animals were measured every two months on average. Three age groups (birth to 6 months for stage 1, 7 to 19 months for stage 2, and 20 to 34 months for stage 3) were defined. Each stage was treated as a different character and a three-trait animal model was applied for the estimation of variance components. Heritabilities for Breton for each stage ranged from 0.05 to 0.36, 0.16 to 0.54, and 0.08 to 0.66, and 0.05 to 0.38, 0.03 to 0.76, and 0.23 to 0.84 for Percheron. Genetic correlations between stages were all positive in both breeds and ranged from 0.37 to 1.00.

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