No abstract

The effect of dietary starch and fat content on serum creatine kinase (CK) activity and substrate availability was evaluated in 4 mares of Quarter Horse-related breeds with polysaccharide storage myopathy (PSSM). Four isocaloric diets ranging in digestible energy (DE) from 21.2% (diet A), 14.8% (B), 8.4% (C), to 3.9% (D) for starch, and 7.2% DE (diet A), 9.9% (B), to 12.7% DE (diet C and D) for fat were fed for 6-week periods (4 weeks with exercise) using a 4 X 4 Latin square design. Postprandial glucose and insulin responses were measured, and 4 hours postexercise, serum CK activity, glucose, insulin, free fatty acids (FFA), and beta-hydroxybutyrate (beta-HBA) were analyzed. Glycogen, glucose-6-phosphate, citrate synthase, 3-hydroxy-acyl-CoA dehydrogenase, lactate dehydrogenase as well as abnormal polysaccharide and lipid content were measured in middle gluteal muscle samples. Postprandial insulin and glucose response was higher for diet A versus D. Log CK activity was higher with diets A, B, and C versus D. Daily insulin was higher and FFA lower on diet A versus B, C, and D, whereas glucose varied only slightly with diet. Muscle oxidative capacity and lipid stores were low in PSSM horses and muscle glycogen and abnormal polysaccharide content high on both diets A and D. Individual variation occurred in the response of PSSM horses to diets differing in starch and fat content. However, for those horses with clinical manifestations of PSSM, a diet with <5% DE starch and >12% DE fat can reduce exertional rhabdomyolysis, potentially by increasing availability of FFA for muscle metabolism.

Energy balance studies using indirect calorimetry were conducted with four mature equids ranging in weight from 125 to 856 kg. Each animal was fed three different levels of intake of the same diet. The amounts of digestible and metabolizable energy required for zero energy balance were determined by calculating regression equations for energy balance against energy intake. It was concluded that the maintenance requirements of equids vary linearly with body weight. No advantage was found for the use of weight for the comparison of equids within the range studied. The digestible energy (DE) requirement for equids confined to metabolism stalls was DE (kcal/d) = 975 + 21.28 X W where W equals body weight in kg. If a factor for activity similar to that suggested by the National Research Council was included, the requirement could be calculated by the equation: DE (kcal/d) = 1,375 + 30.0 X W.

Summary The purpose of this study was to examine the effects of an external nasal strip (NS), frusemide (FR) and a combination of the 2 treatments (NS + FR) on exercise‐induced pulmonary haemorrhage (EIPH) in Thoroughbred horses. It was hypothesised that both the NS and FR would attenuate EIPH as assessed by red blood cell count in bronchoalveolar lavage fluid. In random order, 8 horses completed each of 4 sprint exercise tests on a treadmill: 1) NS; 2) FR (0.5 mg/kg bwt i.v., 4 h pre‐exercise); 3) NS + FR; and 4) control (C; no treatment). After a 5 min warm‐up (4.5 m/s), horses completed 2 min running at 120% maximum oxygen consumption (Vo2max) with the treadmill set at 3° incline. Mean ± s.d. running speed was 14.2 ± 0.2 m/s. In the FR and NS + FR trials, horses carried weight equal to that lost as a result of frusemide administration. During exercise at 120%V̇O2max, oxygen consumption (Vo2) and carbon dioxide production (Vco2) were measured at 15 s intervals. Plasma lactate concentration was measured in samples collected before exercise, at the end of the sprint and after 5 min cooldown at the trot. Thirty minutes after the run, bronchoalveolar lavage (BAL) was performed and the red cell count in the fluid quantified. Vo2 and Vco2 were significantly lower in NS and NS + FR trials than in the C and FR trials at the end of the sprint exercise protocol. However, plasma lactate concentrations did not differamong treatments. Compared with the C trial (61.1 ± 30.5 × 106 red blood cells/ml BAL fluid), pulmonary haemorrhage was significantly (P<0.05) decreased in both the NS (15.9 ± 4.0 × 106 RBC/ml) and FR (12.2 ± 5.8 × 106 RBC/ml) trials. EIPH in the NS + FR trial (7.9 ± 1.0 × 106 RBC/ml) was further diminished (P<0.05) compared to the NS trial, but not different from the FR trial. We conclude that both the external nasal strip and frusemide attenuate pulmonary haemorrhage in Thoroughbred horses during high‐speed sprint exercise. The external nasal strip appears to lowerthe metabolic cost of supramaximal exertion in horses. Given the purported ergogenic effects of frusemide, the external nasal strip is a valuable alternative for the attenuation of EIPH.

The aim of this study was to determine whether the glycaemic/insulinaemic responses to hay with non-structural carbohydrate (NSC, soluble carbohydrate) of 17% (HC), 10% (MC) or 4% (LC) differs in control horses and whether these responses differ between control and horses with polysaccharide storage myopathy (PSSM). Five clinically normal control horses and seven PSSM horses, all unfit and of Quarter Horse breeding (age 9.4 ± 3.4 years, body condition score range: 4.5-6). A crossover design compared the HC and LC hay, with horses randomly assigned to hay type for 5 days, and all horses fed the MC hay during washout, after which the diets were switched. Horses were fed 1.5% BW (as fed) divided into 2 feeding per day, no grain. On morning of the fifth day of each block (seventh day for washout), horses were given 0.5% BW in hay, blood was drawn before and every 30 min for 5 h after feeding, and the rate of intake was measured. Whole blood glucose and plasma insulin were measured. The intake rate was significantly higher for HC. In control horses, the insulin area under the curve (6891.7 ± 3524.2 HC vs. 1185.4 ± 530.2 LC) was significantly higher than LC. Polysaccharide storage myopathy horses had significantly higher glycaemic and insulinaemic responses to HC vs. LC, however; the magnitude of insulin response was lower and glucose response higher in PSSM vs. control horses. Results suggest that insulin responses can differ significantly with the NSC content of hay. Feeding hay with 17% NSC produces elevations in insulin that could be detrimental for PSSM horses.