Feeding & Weight Disorders

Body Composition

Percent body fat can be measured by Dual Energy X-ray absorptiometry (DEXA) or MRI and with these techniques, segmentation of visceral and subcutaneous fat in the dog is feasible. A further advantage of these imaging techniques is that repeated assessments in the same animal are feasible for longitudinal study designs. The obese dogs, having stabilized to their increased body weight, were given DEXA scans and then placed on a restricted diet in which food intake was reduced by 15% for 3 months.

The figures below illustrate changes in body composition and blood chemistry following dietary manipulation. (A) Reducing caloric intake for 3 months led to marked reduction in total body fat and a much smaller reduction in lean mass as measured using DEXA imaging. (B) Secondary measures of clinical chemistry revealed this dietary restriction regimen to significantly reduce blood cholesterol and glucose levels compared to baseline.

Change in Body Composition in Obese Dogs following 3 Months of Caloric Restriction.
Representative data showing how measures of blood chemistry change following a period of reduced food intake. In this experiment, the dogs were all obese at baseline, with body fat being greater than 25% of total body mass. ** = significant <.01 (T-test; two tailed).

Food Intake & Body Weight

In a representative study, 14 neutered beagle dogs of both sexes were fed their normal laboratory diet (Purina Pro Plan) once daily for half hour per day, but at an individually increased level, with the goal of raising body fat to a level of 25%. Collectively, body weight increased progressively over a four month period, with an overall group increase of 42 % compared to baseline. As a group, the animals achieved this level of body fat within 4 months. The increase in body fat was accompanied by modifications in several blood chemistry parameters. There were, however, individual differences: most but not all animals became obese, indicating that dogs can also model the individual differences seen in human obesity.

The figure above shows the weekly body weight for each of the 14 animals given increased rations, fed once per day allowing for precise timing of drug treatment. The dogs self stratified into three groups; those that showed a marked increase in weight and associated obesity, a second group that demonstrated a moderate increase in obesity and a single dog that did not increase in weight. All but one animal responded to increased food availability by progressively increasing body weight, leading to development of obesity.

Glucose Tolerance & Insulin Sensitivity

Glucose tolerance and insulin sensitivity tests can also be built into the test design. An intravenous glucose tolerance test measures the blood glucose levels following an intravenous bolus of dextrose in a fasted dog and is a measure of glucose intolerance.

Intravenous glucose tolerance test data for lean and obese dogs

The figure above shows intravenous glucose tolerance data from lean and obese dogs. This basic test can be modified in a number of ways to determine insulin resistance. The insulin sensitivity index can be calculated based on insulin assay at the same time as the glucose determinations. The classical gold standard test used to determine insulin sensitivity is the hyperinsulinaemic euglycemic clamp technique. Alternatively, the frequently sampled intravenous glucose tolerance test has been used to quantify insulin sensitivity in the dog.

Palatability

Palatability is defined as the subjective pleasure associated with eating a given food over another.

We can provide two different means of assessing palatability. The first, the two pan test, is the industry standard, in which subjects are given a choice of eating two different foods, and the preferred food is the most palatable. The second, the cognitive palatability assessment protocol (CPAP), was developed as an alternative by CanCog to provide a means of testing palatability that require smaller quantities of food. The CPAP is ideal for establishing preference of:

Satiety inducing diets
Small quantities of test food (e.g., tablets)

The figure above demonstrates the preference for lamb based food over time in dogs tested on the CPAP.
In contrast to the previous figure, preference ratios established during two pan testing demonstrate high individual variability. For example, Morpheus showed a large preference for the lamb-based product during CPAP testing, but his preference ratios were more sporadic during two-pan testing. On the other hand, Apollo showed high levels of preference for the lamb based diet during CPAP testing, but almost no preference according to two-pan testing.

Satiety Assessment

Our satiety assessment protocol provides a behavioural measure is independent of food intake that is sensitive to the experience of satiety. The target measure is latency to make a response in learning task requiring mental effort. More specifically, the task requires the animals to hold information in memory for either 5, 55 or 105 seconds and then respond. Animals that are highly food motivated will respond more rapidly than animals experience satiety.

Data from an experiment in which animals are tested either before feeding or following a period of overfeeding, in which animals were given 1 hour to consume a quantity of food containing twice their daily energy requirements. In the overfeeding condition, the animals respond more slowly than in the pre-feeding condition, and the differences when the delay is increased, requiring greater effort.