Effect of Exercise Conditioning on Countering the Effects of Obesity and Insulin Resistance in Horses-A Review

Obesity is an important health concern in horses, along with humans and companion animals. Adipose tissue is an inflammatory organ that alters the insulin-signaling cascade, ultimately causing insulin dysregulation and impaired glucose metabolism. These disruptions can increase the risk of metabolic disease and laminitis in horses and may also impact energy metabolism during exercise. A single bout of exercise, along with chronic exercise conditioning, increases insulin sensitivity and glucose disposal via both contraction- and insulin-mediated glucose uptake pathways. Regular exercise also increases calorie expenditure, which can facilitate weight (as body fat) loss. This paper explores the metabolic pathways affected by adiposity, as well as discusses the impact of exercise on insulin metabolism in horses.

Visual Assessment of Adiposity in Elite Hunter Ponies

Obesity is a critical problem in the equine industry, with ponies being at particularly high risk of developing obesity-related conditions such as metabolic syndrome and laminitis. The purpose of this study was to estimate the level of adiposity in an elite level of competitive show ponies, and to determine if adiposity was related to performance based on their model score (judged on conformation and appearance). Two researchers visually evaluated the body condition score (BCS) and cresty neck score (CNS) of 377 ponies at a national hunter competition. Thirty five percent of the ponies in the competition were considered obese, with BCS scores of 7 or higher. Mean BCS of the ponies was 6.7 ± 0.6 with a range of 5.25 - 8.25 and mean CNS was 2.8 ± 0.6, with a range of 1.75 - 4.5. Medium ponies had higher BCS (P<0.0001) and higher CNS (P=0.015) than the large ponies. There was a tendency for a relationship between body condition score and the model score in all ponies (r = 0.08; P = 0.059), and this was stronger within the large ponies (r =0.20; P <0.01). These findings show that elite competition ponies are dangerously overweight and that adiposity may influence performance in a judged event. This is of grave concern to the horse industry and needs to be addressed.

105 Chromium propionate improves insulin sensitivity in horses following oral concentrate consumption

Forty-eight Quarter Horse geldings (3–8 yr of age) were used to determine the effects of dietary chromium (Cr), in the form of Cr propionate (Cr Prop), on insulin sensitivity. Horses were blocked by age, body condition score, and glucose response to concentrate feeding on d 0, and randomly assigned to treatments. Treatments consisted of 0, 2, 4, or 8 mg Cr/d from Cr Prop. Horses were fed daily a concentrate mix at a rate of 0.2 kg/100 kg BW and grass hay at 1.75 to 2.0 kg/100 kg BW. After an overnight fast, jugular blood samples were obtained at 0, 2, and 4 h after concentrate feeding on d 0 and 28 for determination of glucose and insulin. Plasma glucose on d 28 was affected (P &lt; 0.05) by treatment, time, and treatment x time. Horses fed 4 mg Cr/d had lesser (P &lt; 0.05) plasma glucose concentrations than those in the other treatments at 0 h. At 2 h post feeding glucose concentrations were greater (P &lt; 0.05) in control horses than in those given 4 mg Cr. Horses fed 2 mg Cr/d had lesser (P &lt; 0.05) plasma glucose at 4 h post feeding compared to controls. Plasma glucose did not differ among horses receiving 2 or 4 mg Cr/d at 2 or 4 h. Insulin concentrations were greater (P &lt; 0.05) in horses fed 0 or 2 mg Cr/d than in those given 4 or 8 mg Cr at 0 h. At 4 h post feeding insulin concentrations were greater (P &lt; 0.05) in control horses than in those fed 2 or 4 mg Cr/d. Results of this study indicate that 2 or 4 mg Cr/d from Cr Prop increased insulin sensitivity in adult horses following oral carbohydrate consumption.

Chromium propionate increases insulin sensitivity in horses following oral and intravenous carbohydrate administration

Forty-eight Quarter Horse geldings (3 to 8 yr of age) were used to determine the effects of dietary chromium (Cr), in the form of Cr propionate (Cr Prop) on insulin sensitivity. Horses were blocked by age, body condition score, and glucose response to concentrate feeding on day 0 and randomly assigned to treatments. Treatments consisted of 0, 2, 4, or 8 mg Cr/d from Cr Prop. Horses were fed daily a concentrate mix at a rate of 0.2 kg/100 kg body weight (BW) and grass hay at 1.75 to 2.0 kg/100 kg BW. All horses were fed the control diet for 7 d prior to the initiation of the study. After an overnight fast, blood samples from the jugular vein were obtained at 0, 2, and 4 h after concentrate feeding on days 0 and 28 for the determination of glucose, nonesterified fatty acids, and insulin. A glucose tolerance test (GTT) was conducted on day 42. Glucose was infused via jugular vein catheters, and blood samples were collected at various times relative to dosing for glucose and insulin determination. Plasma glucose on day 28 was affected (P < 0.05) by treatment, time, and treatment × time. Horses fed 4 mg Cr/d had lesser (P < 0.05) plasma glucose concentrations than those in the other treatments at 0 h. At 2 h post-feeding glucose concentrations were greater (P < 0.05) in horses fed 0 or 8 mg Cr/d than in those given 4 mg Cr. Horses fed 2 mg Cr/d had lesser (P < 0.05) plasma glucose at 4 h post feeding compared with those fed 0 or 8 mg Cr. Plasma glucose did not differ among horses receiving 2 or 4 mg Cr/d at 2 or 4 h. Serum insulin was affected (P < 0.05) by treatment, time, and treatment × time. Insulin concentrations were greater (P < 0.05) in horses fed 0 or 2 mg Cr/d than in those given 4 or 8 mg Cr at 0 h. At 4 h post-feeding insulin concentrations were greater (P < 0.05) in horses given 0 or 8 mg Cr than in those fed 2 or 4 mg Cr/d. Plasma glucose was affected (P < 0.05) by treatment and time, but not by treatment × time following the GTT. Mean plasma glucose (across sampling times) concentrations were greater (P < 0.05) in controls than in horses fed 2 or 4 mg Cr/d. Glucose concentrations following the GTT did not differ among controls and horses given 8 mg Cr/d. Following glucose infusion, serum insulin concentrations were greater (P < 0.05) in horses fed 2 or 4 mg Cr and tended to be greater in those fed 8 mg Cr/d compared with controls. The results of this study indicate that 2 or 4 mg Cr/d from Cr Prop increased insulin sensitivity in adult horses following oral carbohydrate consumption.

Alterations in Intestinal Permeability: The Role of the "Leaky Gut" in Health and Disease

All species, including horses, suffer from alterations that increase intestinal permeability. These alterations, also known as "leaky gut," may lead to severe disease as the normal intestinal barrier becomes compromised and can no longer protect against harmful luminal contents including microbial toxins and pathogens. Leaky gut results from a variety of conditions including physical stressors, decreased blood flow to the intestine, inflammatory disease, and pathogenic infections, among others. Several testing methods exist to diagnose these alterations in both a clinical and research setting. To date, most research has focused on regulation of the host immune response due to the wide variety of factors that can potentially influence the intestinal barrier. This article serves to review the normal intestinal barrier, measurement of barrier permeability, pathogenesis and main causes of altered permeability, and highlight potential alternative therapies of leaky gut in horses while relating what has been studied in other species. Conditions resulting in barrier dysfunction and leaky gut can be a major cause of decreased performance and also death in horses. A better understanding of the intestinal barrier in disease and ways to optimize the function of this barrier is vital to the long-term health and maintenance of these animals.

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.

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

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.

Dietary energy source and physical conditioning affect insulin sensitivity and skeletal muscle glucose metabolism in horses

REASONS FOR PERFORMING STUDY

Starch rich (S) feeds reduce insulin sensitivity in untrained horses when compared to high fat (F) feeds, but insulin sensitivity is not affected when S or F are fed during exercise training. The effects of S vs. F on training-associated alterations in skeletal muscle glucose metabolism are unknown.

OBJECTIVES

To determine the effects of dietary energy source on training-associated changes in insulin sensitivity, skeletal muscle GLUT4 protein and hexokinase (HK) and glycogen synthase (GS) activities in horses.

METHODS

After a baseline period on an all forage diet (Phase 1), horses were adapted to high starch (S) or high fat (F) diets (n = 7/group) for 6 weeks (Phase 2) and then completed 7 weeks of exercise training (Phase 3) on the same diets. To measure insulin sensitivity (SI), minimal model analysis of a frequently-sampled i.v. glucose tolerance test was performed at the end of each phase. Middle gluteal muscle biopsies to measure GLUT-4 protein content, muscle glycogen and HK and GS activities were taken before and after euglycaemic-hyperinsulinaemic clamps administered after each phase. Data were analysed by repeated measures ANOVA.

RESULTS

In S, SI was 36% lower (P < 0.05) after Phase 2 when compared to Phase 1 but was unchanged in F. After Phase 3, SI was increased (P < 0.01) in S and F compared to Phase 2 and did not differ (P > 0.05) between diets. Middle gluteal muscle GLUT-4 protein and post clamp HK activity were increased (P < 0.05) in S after Phase 3, with higher (P < 0.01) GLUT4 in S than in F. GS activities were unchanged in both diets.

CONCLUSIONS

Adaptation to S resulted in decreased SI mitigated by moderate physical conditioning. Increased GLUT-4 protein content and HK activity in S may have contributed to higher SI after training.

Undergraduate performance in a domestic animal laboratory taught via distance education

The objective of this study was to determine if laboratory modules of an undergraduate animal anatomy course offered in distance education (DistEd) format were as effective as face-to-face (F2F) format in helping students learn. Students (n = 159) completed an anatomy pretest as well as a presurvey to assess prior DistEd experience. Alternating each week, laboratory topics were presented either as F2F or as virtual DistEd laboratories. Two laboratory examinations were administered and included material from both laboratory formats (DistEd and F2F). Questions from the pretest were also included and used to generate the posttest scores. At the end of the semester, students completed a postsurvey to determine if DistEd was a viable alternative to F2F. Student grades on each examination were compared using an ANOVA model that included main effects of presentation method (DistEd, F2F), semester (fall, spring), and their interaction. Learning was evaluated based on the performances of students on pre- and posttests using unpaired t-tests. There was an increase (P < 0.0001) in anatomy post- vs. pretest scores for both semesters, indicative of student learning, although there was no effect of presentation method (F2F or DistEd). On exam 1, students achieved greater scores in fall 2008 (P < 0.0001) on material presented via DistEd compared with that presented as F2F. However, in spring 2009 students scored better on material presented as F2F. There was no effect of presentation method on exam 2 scores for either semester. Based on the postsurvey, 79.3% of students in fall 2008 and 52% of students from spring 2009 agreed that DistEd laboratories were a viable alternative to F2F laboratories. The results of this study support the conclusion that anatomy material can be taught effectively by distance education methods.