THE EFFECTS OF FEEDING PULSE-BASED, GRAIN-FREE, DIETS ON DIGESTIBILITY, GLYCEMIC RESPONSE, AND CARDIOVASCULAR HEALTH IN DOMESTIC DOGS
The following thesis will focus on the effects of feeding pulse-based, grain-free, diets on digestibility, glycemic response, and cardiovascular health in dogs. In July of 2018, the United States Food and Drug Administration reported a link between grain-free diets and dilated cardiomyopathy (DCM) in dogs. Despite this, there is no definitive evidence confirming or demonstrating that grain-free diets are unsafe to feed to dogs. Due to this statement, there is currently major controversy surrounding whether or not pet owners should be feeding grain-free diets to dogs. The first study conducted was a 7-day short-term feeding trial that involved six different experimental diets. All diets were formulated to include 20% available carbohydrate using either rice (grain-containing) or pulse flours from either smooth pea, fava bean, red lentil, or wrinkled pea varieties (4140-3 or Amigold). It was hypothesized that dog diets with higher levels of dietary fiber would produce a lowered glycemic response due to decreased rates of digestion and lowered bioavailability of macronutrients, as well as increased fecal bile salt excretion. This in turn was hypothesized to produce lowered plasma concentrations of cystine, cysteine, methionine, and taurine. This study demonstrated that pulse-based diets have the potential to reduce postprandial glucose response, which is beneficial for dogs. After 7-days of feeding each diet, there was a trend of reduced fasted plasma taurine levels in the dogs consuming pulse-based diets, with exception to the lentil diet. However, all plasma taurine levels remained within normal limits. Decreased apparent total tract digestibility of macronutrients and amino acids were also observed and associated with increasing levels of both amylose and dietary fiber, however, a specific causative agent for this could not be determined due to the nature of this study. Surprisingly, increases in dietary fiber within the diets led to decreased fecal bile acid excretion. The second study was a longer 28-day feeding study, that tested the pulse-based diets with the highest and lowest levels of amylose from study one and compared them to an experimental rice-based diet and a commercial grain-containing diet. For the second study, it was hypothesized that dogs fed pulse-based, grain-free diets for 28 days would cause decreased apparent total tract digestibility of macronutrients, increased fecal bile acid excretion, and decreased plasma levels of cystine, cysteine, methionine, and taurine, resulting in sub-clinical cardiac or blood changes indicative of early stages of DCM. After conducting echocardiography, it was observed that the high amylose wrinkled pea (Amigold) diet in study two increased left ventricular size and volume, as well as increased plasma levels of NT-ProBnP, in a sub-clinical manner that was reversible. These cardiac changes representative of early-stage DCM are possibly associated with the increased level of amylose within the wrinkled pea (Amigold) diet. The second study confirmed from study one that grain-free diets did not cause plasma taurine levels to fall below normal limits. After consuming all diets (both grain-containing and grain-free), plasma levels of taurine were unchanged and remained within normal limits. In contrast, all grain-containing and grain-free diets caused reduced plasma methionine levels. Similar to study one, apparent total tract digestibility of macronutrients and amino acids, excluding taurine, was reduced when the dogs consumed the pulse-based diets possibly due to higher levels of fiber. Both studies showed pulse-containing diets decreased fecal bile acid excretions. Overall, slight DCM-like changes from the wrinkled pea diet, but not the lentil diet, demonstrated that not all grain-free diets can be treated the same. In addition to this, if diet-induced DCM-like changes are in fact associated with increased levels of dietary amylose, this could pose an issue to both grain-free and grain-containing diets. This complicates the original claim made by the FDA regarding grain-free diets, as diet-induced DCM in dogs may not be exclusively associated with grain-free diets.
Digestibility, Glycemic Response, Taurine, Dilated Cardiomyopathy, Pulses, Fiber, Amylose
Master of Science (M.Sc.)
Veterinary Biomedical Sciences
Veterinary Biomedical Sciences