Objective - To determine whether mild restriction of food intake affects clinicopathologic variables, body composition, and performance of dogs undertaking intense sprint exercise. Animals - 9 trained healthy adult Greyhounds. Procedure - Dogs were offered food free choice once daily for 9 weeks until body weight and food intake stabilized. Dogs were then randomly assigned to be fed either 85% or 100% of this quantity of food in a crossover study (duration of each diet treatment period, 9 weeks). Dogs raced a distance of 500 m twice weekly. Clinicopathologic variables were assessed before and 5 minutes after racing; food intake, weight, body composition, body condition score, and race times were compared at the end of each diet period. Results - Compared with values associated with unrestricted access to food, there were significant decreases in mean body weight (by 6%) and median body condition score (from 3.75 to 3.5 on a 9-point scale) and the mean speed of the dogs was significantly faster (by 0.7 km/h) when food intake was restricted. Body composition and most clinicopathologic variables were unaffected by diet treatment, but dogs given restricted access to food had slightly fewer neutrophils, compared with values determined when food intake was unrestricted. Conclusions and clinical relevance - Results indicate that the common practice among Greyhound trainers of mildly restricting food intake of racing dogs to reduce body weight does improve sprint performance. A body condition score of approximately 3.5 on a 9-point scale is normal for a trained Greyhound in racing condition.