Question

I have a three-year-old Quarter Horse that tested positive for polysaccharide storage myopathy (PSSM). I have been feeding Re-Leve Concentrate since May. His current diet includes 2 lb (0.9 kg) Re-Leve Concentrate, 4 oz canola oil, and 1 oz of salt in the morning and evening. He grazes Bermudagrass as he chooses. He has not had an episode of tying-up since I have switched to Re-Leve Concentrate, and I am thankful for this. When I run a blood chemistry on him, his bilirubin levels are always elevated. Is this common for horses on high-fat diets? I also noticed that this summer, in the Oklahoma heat, he would sweat at a lower temperature than my other horses. Again, I wonder if this is typical of horses fed high-fat diets. Thanks for any insight.

Answer

I am glad to hear your current nutrition program, of which Re-Leve is a significant part, is helping manage your Quarter Horse with PSSM.

Most horses can tolerate 10-20% of their digestible energy (calorie) requirement as dietary fat.

In the early 2000s, researchers investigated the effect of feeding horses high-fat versus high-starch diets for 390 days. This study reported that no apparent adverse effects of long-term high fat feeding were identified. Plasma bilirubin concentration was unaffected by diet type in this study. The amount of fat fed in this study (0.88 g fat/kg body weight/d) is comparable to the amount of fat provided by your diet.

I estimated that your current diet is providing about 500 g of fat from Re-Leve Concentrate (4 lb/day) and canola oil (8 oz/day). Based on a body weight of 1,100-1,150 lb (500-525 kg), this provides between 0.88-1.0 g fat/kg body weight/day. These results are in line with a study conducted by Kentucky Equine Research that observed no adverse effects in two-year-old Thoroughbreds fed supplemental fat for seven months.

Is your horse showing any other signs associated with hyperbilirubinemia, or is it just his values falling outside the reference range? Several factors can affect bilirubin concentrations, so working with your veterinarian to investigate this further is best.

For horses exercising in hot and humid conditions, feeding a high-fat diet or replacing other feedstuffs with dietary fat is recommended, as it helps reduce the amount of metabolic heat produced from digestion, so there is less heat for the exercising horse to dissipate. If this is the first year your horse is in regular exercise, it may be the first time you have noticed that he seems to be more of a sweater than your other horses. This may be natural for him, but I would monitor this. If it becomes more chronic or profuse, I would discuss this with your veterinarian.

In sum, I believe the hyperbilirubinemia and the unusual sweating are unrelated to the high-fat diet.