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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., (© 2010 Blackwell Verlag GmbH.)

To delay the onset of fatigue, endurance horses are often fed at rest stops during races. The resulting increase in blood insulin may adversely inhibit lipolysis. In humans, ingestion of fructose produces a smaller insulin rise than glucose. This study compared glucose and fructose as carbohydrate supplements for endurance horses. Three Arabian geldings were given 300 g of fructose (F), glucose (G) or 50% glucose: 50% fructose (GF), in 1.5 L water, by stomach tube. In the Resting Test, carbohydrate was administered at rest. Following treatment, blood samples were taken every 30 min for 8 h, and feces were collected for 24 h. Treatment did not affect fecal weight or water content. Plasma glucose and insulin responses did not differ among treatments. Post-treatment (60 min), plasma L-lactate tended to be higher (P = 0.06) after the F and GF treatments than after the G treatment. In the Exercise Test, two treadmill exercise bouts at 0 degrees incline (Bout 1: 90 min; Bout 2: 120 min) were separated by a 1-h rest period. A total distance of 36.84 km was covered at a mean speed of 2.9 m/s. Carbohydrate was administered 45 min before Bout 2. Plasma glucose and insulin at the start of Bout 2 were higher (P = 0.02 and 0.03, respectively) with the GF treatment than with the F treatment. However, during exercise, plasma glucose concentrations did not differ among treatments. We conclude that fructose is well-absorbed by horses and rapidly converted to glucose.

This study looked at the effect of feeding diets supplemented with either a predominantly saturated or unsaturated vegetable oil over a prolonged period to exercising horses. Eight Thoroughbred horses were assigned to 2 diet treatments and for 10 months were fed Timothy hay and oats, together with a fortified sweet feed supplemented with either a predominantly unsaturated (Un) or a saturated (S) vegetable oil so that approximately 19% DE (Digestible Energy) came from dietary fat and approximately 12% from either the Un or S source (AC). An increased amount of Un or S fortified sweet feed, replacing the oats, was then fed for a further 6 months (HF) so that approximately 27% DE came from fat and approximately 20% from the Un or S vegetable oil. Standardised incremental treadmill exercise (8-12 m/s) tests (STEP) and duplicate oral glucose tolerance tests (TOL) were carried out after 3, 6 and 9 months of the AC diet and after 3 and 6 months on the HF diet. There was no significant effect of dietary treatment or when the tests were undertaken (time) on the insulin or lactate responses to the STEP tests. Overall there was a significant (P < 0.05) effect of time and treatment on the glucose response, but there was no difference between treatments at the first and last tests or between the results for these tests or between the endAC and endHF tests. No significant effect of treatment or time was seen on the TOL glucose response (% change from Time '0') although there was a trend for the glucose concentrations to be lower and the insulin responses higher (nonsignificant) in the S treatment group. No significant effect of treatment on haematological parameters, monitored monthly, was found. Total protein and gamma glutamyl transferase remained within the normal range throughout. There was a significant effect of treatment (P < 0.05) on cholesterol and triglycerides with higher concentrations in the S group from the first (1 month) sample. Linoleic acid was the main fatty acid in all the 4 plasma lipid classes with slightly, but significant (P < 0.05), higher concentrations in Un for the cholesterol ester and phospholipid classes. There was no effect of time. Overall, the total resting plasma fatty acid content was significantly higher (P < 0.05) with S at the sample points (endAC and endHF). No adverse effects of feeding either diet on apparent coat condition or hoof appearance were seen apart from an apparent increase in the grease score. Many of the parameters assessed showed significant improvements with time (P < 0.05). In conclusion, no apparent adverse effects of feeding a diet supplemented with either an unsaturated or saturated vegetable oil for 6 months at approximately 20% DE after 10 months at approximately 12% DE were identified and there were no apparent disadvantages of feeding a saturated vegetable oil supplemented diet compared with an unsaturated one.

High-grain diets for the exercising horse were compared with diets which provided 15% of the total caloric intake from either vegetable oil or a highly fermentable fibre source (beet pulp). Six Thoroughbreds age 3 years were fed one of 3 diets or 5 weeks in a replicated 3 x 3 Latin square. The CONTROL diet was 3.65 kg of sweet feed (SF), 0.9 kg of a protein/vitamin/mineral pellet and 5.45 kg of hay cubes. The FAT diet replaced 1.15 kg of SF with 0.45 kg of soybean oil and the FIBRE diet replaced 1.15 kg of SF with 1.36 kg of beet pulp. Horses were exercised 3 times per week on a high-speed treadmill. During the last week of each period, the horses performed a standardised exercise test (SET). A series of blood samples was drawn immediately before feeding and every 0.5 h for 3 h after feeding, throughout the exercise bout and 30 min post exercise. Plasma was analysed for lactate, glucose, cortisol, insulin, packed cell volume, total protein and triglycerides. Water intake was measured at regular intervals during SET day. Blood glucose was lower (P < 0.05) in the FAT-fed horses during the 3 h post feeding as compared to either CONTROL or FIBRE-fed horses. Insulin was lower (P < 0.05) in the FAT-fed both post feeding and throughout exercise. Cortisol was lower (P < 0.05) in the FAT than the CONTROL-fed during exercise. Following exercise, the FAT-fed drank more water (P < 0.01) than either CONTROL or FIBRE-fed. Substituting 15% of DE as vegetable oil had a greater effect on metabolic response to exercise than a 15% substitution of beet pulp.

Six Thoroughbreds were used to evaluate time of feeding on changes in exercise response in horses receiving either a textured feed or a fat-supplemented textured feed. Using a crossover design, 3 horses were fed a fat-supplemented diet while 3 horses received a control ration of textured feed. Horses performed a standardised exercise test (SET) on a high speed treadmill. The SET was performed at 3 different times: 1) following an overnight 12 h fast, 2) 3 h after feeding and 3) 8 h after feeding. The SET consisted of a 2 min walk at 1.4 m/s, 800 m trot at 4.2 m/s, 800 m gallop at 7.7 m/s, 1600 m gallop at 11 m/s, 800 m trot at 4.2 m/s and 2 min walk at 1.4 m/s. Jugular blood samples were taken before feeding, hourly until the beginning of the SET, at the end of each exercise step, 15 min post exercise and 30 min post exercise. During the SET, heart rate was measured and blood samples collected for analysis of glucose, lactate, insulin and nonesterified fatty acids (NEFA). Feeding horses 3 h prior to exercise resulted in elevated concentrations of plasma glucose and insulin (P < 0.01) at rest. Elevated concentrations of insulin in horses fed 3 h prior to exercise decreased plasma glucose (P < 0.01) during exercise and appeared to have suppressed fat oxidation during exercise because horses that were either fasted or fed 8 h post prandial had a net disappearance of NEFA in the plasma during exercise. This study indicates that beginning exercise with elevated plasma insulin appeared to be of no benefit during the exercise conducted in this experiment.

Twenty-two pony mares were fed one of three diets that provided 93.0, 74.8 or 57.2 kcal of digestible energy (DE) per kg body weight per day. Milk samples were taken at 14 day intervals. A total of five samples were taken from each mare. The samples were analyzed for total solids, crude protein, lactose, total lipids, ash, calcium and phosphorus. Gross energy was calculated from composition data. Increases in energy intake decreased the concentration of total solids, protein, fat and gross energy of mare's milk. Energy intake had a greater influence on the mare's body condition than on milk energy production. It was concluded the objective of a feeding program for a lactating mare should be to keep the mare in a desirable body condition rather than to influence milk composition or production.