S.E. Pratt-Phillips

The effect of different feed delivery methods on time to consume feed and the resulting changes in postprandial metabolite concentrations in horses1

Management techniques that reduce the insulin response to feeding in horses have application in preventing insulin resistance (IR) and potential associations (e.g., laminitis). Eight mature idle horses of BCS between 5 and 6.5 and with no previous indication of IR were fed a meal of concentrate under 4 feed delivery treatments in a repeated Latin Square design. Treatments were all based on a bucket of equal dimensions. The treatments included a control (CON) and 3 treatments hypothesized to increase time to consume feed (TCF): mobile obstacles above the feed (BALL), stationary obstacles below the feed (WAFF), and feed with water added (WTR). Jugular venous blood samples were taken at feed delivery, every 10 min for the first hour, and then every 30 min until 300 min after feed delivery. The TCF was different across treatment and was greater (P < 0.05) for BALL and WAFF when compared with CON and WTR. Glucose and insulin concentrations increased after feeding (P < 0.05) and tended to differ among treatments (P < 0.10). Peak insulin and glucose concentrations were affected by treatment as were the time to peak insulin and the area under the curve of insulin (P < 0.05). Therefore, feed delivery methods that include obstacles effectively increase TCF and attenuate postprandial glucose and insulin concentrations. A second experiment was designed to determine if the TCF changes associated with BALL and WAFF in Exp. 1 remain effective over a 4-d period. Four horses with no recent or regular history of consuming concentrates were fed concentrate meals for 4 consecutive d using the same treatments described in Exp. 1 and a Latin square design. Horses were subject to a 4-d adaptation period and were randomly assigned to 4-d treatment periods using the 4 previously described treatments. During adaptation, TCF decreased over time (P = 0.02). After adaptation, WAFF had greater TCF when compared with CON and WTR (P < 0.05) whereas WTR had the lowest TCF overall. Using obstacles to increase TCF on a daily basis may be an effective method to reduce postprandial glucose and insulin concentrations, thereby decreasing the risk of IR development in horses.

Comparison among the euglycemic-hyperinsulinemic clamp, insulin-modified frequently sampled intravenous glucose tolerance test, and oral glucose tolerance test for assessment of insulin sensitivity in healthy Standardbreds.

OBJECTIVE To compare, in horses, estimates of insulin sensitivity obtained from minimal model analysis (MMA) of a frequently sampled IV glucose tolerance test (FSIGTT) with estimates from the euglycemic-hyperinsulinemic clamp (EHC) and to evaluate the validity of surrogate estimates of insulin sensitivity derived from an oral glucose tolerance test (OGTT). ANIMALS 18 mature Standardbreds (mean ± SD body weight, 428.9 ± 35.9 kg; mean ± SD body condition score, 4.4 ± 1.0 [on a scale of 1 to 9]). PROCEDURES All horses underwent at least 2 of the 3 procedures (EHC [n = 15], insulin-modified FSIGTT [18], and OGTT [18]) within a 10-day time frame to evaluate insulin sensitivity. RESULTS Insulin sensitivity variables derived from the EHC and FSIGTT were strongly correlated (r = 0.88). When standardized to the same units of measure, these measures were still strongly correlated (r = 0.86) but were not equivalent. Area under the curve, peak insulin concentration, insulin concentration at 120 minutes, and 2 calculated indices from glucose and insulin data from the OGTT were significantly correlated with the EHC- and FSIGTT-derived estimates of insulin sensitivity. CONCLUSIONS AND CLINICAL RELEVANCE In healthy Standardbreds with moderate body condition score, insulin sensitivities from the EHC and FSIGTT were strongly correlated but not equivalent. Estimates derived from an OGTT also may be useful to estimate insulin sensitivity.

Assessment of protein synthesis in highly aerobic canine species at the onset and during exercise training

Canis lupus familiaris, the domesticated dog, is capable of extreme endurance performance. The ability to perform sustained aerobic exercise is dependent on a well-developed mitochondrial reticulum. In this study we examined the cumulative muscle protein and DNA synthesis in groups of athletic dogs at the onset of an exercise training program and following a strenuous exercise training program. We hypothesized that both at the onset and during an exercise training program there would be greater mitochondrial protein synthesis rates compared with sedentary control with no difference in mixed or cytoplasmic protein synthesis rates. Protein synthetic rates of three protein fractions and DNA synthesis were determined over 1 wk using (2)H2O in competitive Alaskan Huskies and Labrador Retrievers trained for explosive device detection. Both groups of dogs had very high rates of skeletal muscle protein synthesis in the sedentary state [Alaskan Huskies: Mixed = 2.28 ± 0.12, cytoplasmic (Cyto) = 2.91 ± 0.10, and mitochondrial (Mito) = 2.62 ± 0.07; Labrador Retrievers: Mixed = 3.88 ± 0.37, Cyto = 3.85 ± 0.06, and Mito = 2.92 ± 0.20%/day]. Mitochondrial (Mito) protein synthesis rates did not increase at the onset of an exercise training program. Exercise-trained dogs maintained Mito protein synthesis during exercise training when mixed (Mixed) and cytosolic (Cyto) fractions decreased, and this coincided with a decrease in p-RpS6 but also a decrease in p-ACC signaling. Contrary to our hypothesis, canines did not have large increases in mitochondrial protein synthesis at the onset or during an exercise training program. However, dogs have a high rate of protein synthesis compared with humans that perhaps does not necessitate an extra increase in protein synthesis at the onset of aerobic exercise training.

Effect of a single bout of exercise and chronic exercise training on insulin sensitivity in racing sled dogs

Two experiments were designed to investigate the role of exercise on insulin sensitivity (IS) in Alaskan racing sled dogs. In both experiments, IS was quantified with an isoglycemic-hyperinsulinemic clamp (IHC), whereby IS was defined as the glucose infusion rate (GIR) divided by the mean insulin concentration during the clamp. In Experiment 1, IS was quantified in 12 racing sled dogs during three stages of exercise training: unexercised for 4 months over the summer (deconditioned), and after two and four months of exercise conditioning. At each stage IS was assessed in unexercised dogs (n=6) and 60 h following a standard exercise challenge (n=6) consisting of a 35.4 km run completed in 2.5 h. In Experiment 2, IS was assessed in deconditioned dogs (n=6) and in well-conditioned dogs that had either completed a 708 km race 5-days prior (n=3) or were unraced for the previous month (n=3). In Experiment 1, there were no significant differences (Pa0.05) in GIR or IS between the three levels of conditioning, nor...

Effect of reduced protein intake on endurance performance and water turnover during low intensity long duration exercise in Alaskan sled dogs

Increased nutritional demands for endurance exercise of dogs are typically met through increased amounts of their current food. As a result, protein intake is also increased, and excessive nitrogen may affect the dog’s water balance. Sixteen unconditioned Alaskan sled dogs underwent a 6-week exercise training protocol, wherein 8 dogs were fed increasing amounts of their normal kibble to maintain body weight, while the other 8 were fed the same amount of kibble, with increasing calorie needs met by equal amounts of sugar and oil. The diets resulted in similar calorie intakes (181.3±20.0 and 205.7±36.3 kcal/kg0.75, for the control and low protein dogs respectively) but control dogs had higher protein intakes (32.2±0.0 and 19.4±2.4% of metabolic energy intake). After 6 weeks of training the dogs completed a 5 day exercise test in which they travelled 24 km per day, where total energy expenditure was determined using doubly-labelled water technique. Dogs expended an average of 1,491±264 kcal/day (145±25 kcal/...