Abstract
Obesity and diabetes are common in dogs, which in human studies have been linked to derangements in insulin sensitivity and macronutrient metabolism. However, unlike human based research, insulin resistance and its consequences have not been extensively studied in the dog. It was therefore the aim of this thesis to establish a suitable method to measure insulin sensitivity in dogs and to investigate the effect of marine fish oil (MFO) supplementation. The glucose/insulin minimal model used to analyse data from the intravenous glucose tolerance test (IvGTT) was constructed from published literature and validated using data from the literature and other groups. To test reproducibility in vivo, three dogs were investigated six times using the IvGTT with model analysis. All dogs showed mean values for insulin sensitivity (S1) of 1.05, 0.75 and 0.76 x104 min-1pM-1, and glucose effectiveness (S G) of 3.32, 2.27 and 2.93 x102 min-1. Mean intraindividual coefficients of variation of 16% (S1) and 46 % (SG) were found. Measures of insulin sensitivity as assessed by the oral and intravenous glucose tolerance tests (OGTT and IvGTT) and the insulin tolerance test (ITT) were each made once in five dogs. The OGTT was considered unsuitable due to rises in plasma glucose late in the test, which were possibly a result of the glucose dose used. Of the other tests the IvGTT appeared more sensitive as the ITT classified a possibly insulin insensitive dog as the most insulin sensitive of the group (IvGTT S1 = 0.53 x 104 min-1pM-1 (range 0.53-2.76), ITT k3-15 = 8.15%/min (range 6.40-8.15)). To assess the effect of MFO supplementation, 6 dogs were compared with MFO enriched and unenriched diets. Intakes of 0.08g EPA and 0.06g DHA per 100g food resulted in high levels of incorporation in red blood cell membranes. Testing with an IvGTT at the end of each diet found no observed effects on insulin sensitivity in the group as a whole. However one dog with a reduced insulin sensitivity (0.53 x104 min-1pM-1) did show an improvement with MFO supplementation (0.94 x 104 min-1pM-1). In conclusion, insulin sensitivity in the dog can be reliably assessed by a number of measures but the best of these appears to be the IvGTT with minimal model analysis. Dietary manipulation to increase intake of MFO does not appear to improve insulin sensitivity in normal dogs. Further studies might focus on dogs with known insulin resistance or those with risk factors for resistance such as age, breed and body composition.