标题：Effect of the Geographic Breeding Region on Digestible Energy Intake and Growth Rate of Thoroughbred Yearling Horses: A Comparison of the Hidaka and Miyazaki Regions of Japan
摘要：Different geographic regions in which thoroughbred yearling horses are bred have different climates and different types of forage in pasture and hay. These factors are likely to influence the energy metabolism and growth rate of yearling horses. However, the effects of the characteristics of geographic regions on the digestible energy (DE) intake and growth rate of thoroughbred yearlings has yet to be clarified in detail. Here, we have examined the effect of the breeding region on growth performance of young horses, by comparing the DE intakes and growth rates of thoroughbred yearlings in Hidaka (Hokkaido) and Miyazaki (Southern Kyushu) in Japan. Eighteen male thoroughbred yearlings were divided equally into two groups, and bred either at the Hidaka training and research center (HYF) or the Miyazaki yearling farm (MYF). Measurements were conducted in September (summer) and in February (winter), and the mean ages of the yearlings during these two periods were 18 months and 23-24 months old, respectively. The apparent digestible energy intake was measured by a double-indicator method using Cr2O3 and lignin. There was no significant difference in the DE intakes between the yearling horses at the HYF and MYF in either season. The warm land of Southwest Japan has been considered to be unsuitable for growing forage containing sufficient nutrients to feed thoroughbreds, but no nutritional disadvantage of this forage was detected in the yearlings bred at the MYF. On the other hand, the heart girth (HG) and cannon circumference (CC) were found to be significantly smaller in yearlings at the HYF, compared to those at the MYF, in the winter evaluation (p<0.05). Significant positive correlations between the ADG and DE intake/100 kg body weight were seen in animals at the HYF in the summer and in those at the MYF in both seasons; however, such a correlation was not found in horses at the HYF in winter. The reason for the smaller HG and CC and the absence of a significant correlation between the ADG and DE intake/100 kg body weight in the yearlings at the HYF in winter is unclear. It could be attributable to growth delay due to exposure to cold temperatures, or lack of supplementation to compensate for the increased energy requirement due to excess energy metabolism in cold weather. Closer attention must, therefore, be paid to the energy supply and nutritional composition of feedstuffs fed to thoroughbred yearlings at farms in regions with cold ambient temperatures.
关键词：digestible energy;growth rate;regional differences in Japan;thoroughbred yearling
