Abstract
Background:
The leucine metabolite β-hydroxy-β-methylbutyrate (HMB) has been extensively studied as a supplement to improve athletic performance in humans; however, data on its efficacy in canine athletes remain limited.

Aim:
To determine the safety and efficacy of calcium HMB (CaHMB) in canine athletes, we conducted two complementary studies with different designs: (1) a randomized trial in racing greyhounds (a sprint athletic model) and (2) an exploratory observational study in mushing dogs (an endurance athletic model).

Methods:
We studied greyhound racing during a 12-week race meet. A total of 37 dogs (18 controls, 19 CaHMB-supplemented receiving 1 g daily) were followed during pre-race training and then throughout the meet, and race times and placings were recorded. Blood was drawn for analysis during the racing period. In a second observational study, 22 mushing dogs (10 control, 12 CaHMB-supplemented, receiving 1 g daily) were studied. Blood chemistry was analyzed after an endurance training event.

Results:
Comprehensive blood chemistry and hematology panels indicated that HMB was safe with no adverse effects. HMB-supplemented greyhounds showed significantly better performance maintenance: race times increased by 0.18 s vs 0.73 s in controls (p < 0.05). Placement rankings improved markedly during the first 2 weeks post-supplementation (−0.78 places for HMB vs. +1.01 places worsened in controls; p = 0.002). In the observational mushing dog study, HMB was well tolerated with no adverse effects. Muscle damage markers (creatine phosphokinase and lactate dehydrogenase) showed numerically lower values in the HMB group. HMB-supplemented mushing dogs demonstrated significantly lower blood glucose (73.25 vs. 82.90 mg/dL; p = 0.03) and cholesterol (218.75 vs. 254.40 mg/dL; p = 0.05), which may reflect metabolic differences.

Conclusion:
These findings establish the safety of CaHMB supplementation in canine athletes and demonstrate significant benefits for sprint performance in a trial, with preliminary observational signals in endurance canine athletes that warrant confirmation in larger controlled trials. Larger controlled studies are needed to confirm efficacy in endurance contexts and to evaluate applicability to aging or sedentary companion dogs.

Key words: Dogs; Endurance; HMB; Safety; Sprinting.