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Some aspects of energy, protein and vitamin E nutrition of the performance horse are discussed. The amount, dietary source and time of ingestion of energy before exercise can influence performance. In 1989 the National Research Council (NRC) increased their estimates of energy required by racehorses. Recent studies indicate that the increase was reasonable. Many factors, however, can influence energy requirements. Therefore, the best measure would be body weight and composition of the horse. A proper balance of soluble carbohydrate, fiber, fat and protein is essential. Some guidelines are presented. The amount and type energy source given before exercise can influence level of plasma glucose and free fatty acids during exercise, but the effects of these changes in the concentration of metabolites remains to be determined. There is no evidence that increased dietary concentrations of protein are needed and, in fact, may impair performance. Supplemental histidine (to enhance carnosine levels) or carnitine appear to be of limited value for horses fed conventional diets. Dietary concentrations of vitamin E less than the 80 IU/kg recommended by NRC seem to adequately protect against exercise-induced peroxidation. The NRC value may be justified on the basis of immune response, but further studies are needed. Vitamin E has been shown to be involved with familial equine degenerative myeloencephalopathy and may be involved with equine motor neuron disease, a condition considered to be similar to amyotrophic lateral sclerosis in humans. [ABSTRACT FROM AUTHOR]

Summary Four mature horses (3 Standardbreds and 1 Thoroughbred) were used in a 4 × 4 Latin square design experiment to investigate the effect of time of concentrate feeding prior to exercise on the metabolic response to exercise. Horses were fasted overnight and then given no feed (fasted) or 1 kg corn grain 1, 3 or 5 h before exercise. Exercise consisted of a warm-up (1600 m at 6.0 m/s) and walk (800 m) followed by a high intensity phase (400 m at increasing speed and 1600 m at 11 m/s; 2% grade). During exercise, plasma glucose decreased in horses fed 1 or 3 h before exercise (P<0.05), but increased in horses fasted before exercise (P<0.05). Plasma insulin declined (P<0.05) during exercise in horses fed 1 or 3 h before exercise but did not change in horses that were fasted or fed 5 h before exercise. For all treatments, peak plasma free fatty acids (FFA) occurred during the walk phase and FFA decreased (P<0.05) during the last 2000 m (11 m/s; 2% grade). At the onset of exercise and during much of the exercise test, plasma FFA were highest in horses that were fasted for 16 h before exercise. Plasma lactate increased during the exercise test but was not affected by treatment (P>0.05). These data indicate that time of feeding prior to exercise can affect metabolic responses of horses to exercise, which could ultimately alter performance. In addition, researchers should consider that time of feeding may affect the interpretation of data from experiments examining the effects of diet and/or training on exercising horses. [ABSTRACT FROM AUTHOR]

Summary The metabolic consequences of submaximal exercise following long term nutritional deprivation were investigated in 6 donkeys. Animals were fed all roughage diets, either adequate (Timothy hay: H) or deficient in energy and protein (wheat straw: S) in a crossover design. After 8-10 weeks of dietary adaptation, responses to 60 min of moderate intensity draft loading exercise were compared. Jugular blood was sampled at rest and during exercise for glucose, lactate and free fatty acids (FFA) concentrations, haematocrit, Cortisol and insulin levels. Heart rate (HR) was monitored electronically. Resting lactate concentration was higher in animals fed hay (H) than in animals fed straw (S); only in S animals, however, did post exercise lactate concentration (1.55 ± 0.9 mmol/l) exceed pre-exercise lactate concentration (0.6 ± 0.1 mmol/l). Hypoglycemia occurred in all animals in early exercise but was more pronounced in S animals. Straw-fed animals had higher FFA concentrations at rest than H animals (mean ± s.e. 433 ± 71 vs. 102 ± 9 μmol/l). Plasma FFA concentrations declined precipitously in S animals at the onset of exercise, thereafter FFA increased over resting concentrations in both diets. Cortisol concentrations were higher at all times in H animals and increased during exercise regardless of diet. Insulin was lower in S animals and decreased during exercise in both diet groups. Resting HR was lower in S than in H animals (mean ± s.e. 34 ± 2 vs. 45 ± 2 beats/min). Exercising HR was greater in S animals. These data suggest that long term undernutrition in donkeys leads to decreased carbohydrate reserves, diminished maximal aerobic capacity and endocrine alterations. Work difficulty and stress level may increase, with possible negative implications for animal health and endurance. [ABSTRACT FROM AUTHOR]

Summary The inter-relationships of calcium and phosphorus were studied in a series of metabolic experiments in young horses and ponies. Graded levels of dietary calcium from 0.15 to 1.5 per cent. had little effect on the metabolism of phosphorus when phosphorus comprised 0.35 to 0.4 per cent. of the diet. Urinary phosphorus decreased when calcium intake increased possibly because more phosphorus was utilized in bone formation. A high phosphorus (1.2 per cent.) diet, adequate in calcium (0.4 per cent.) and with a Ca:P ratio of 0.3:1 decreased the intestinal absorption and retention of calcium. Plasma calcium decreased and plasma phosphorus increased. Bone turnover, measured as the rates of deposition and removal of skeletal calcium was accelerated. These results should be attributed to the high phosphate content of the diet rather than to the Ca:P ratio. Ponies fed a diet composed of similar constituents and Ca:P ratio (0.4:1) but inadequate in calcium (0.15 per cent.) absorbed calcium with high efficiency. Plasma calcium and phosphorus and the rate of deposition of calcium in bone were unaffected by diet. However, the rate of removal of calcium from bone was increased in response to the low calcium diet. Addition of phosphorus as inorganic phosphate or sodium phytate (0.6 to 0.8 per cent.) to a diet adequate in calcium (0.43 per cent.) appeared to inhibit calcium absorption but did not affect the concentration of calcium or phosphorus in blood plasma. The effect of phosphorus added as sodium phytate was similar to that of phosphorus added as inorganic phosphate. The Ca:P ratio should be greater than unity but further studies are needed to define the ratio more closely. However, the absolute intake of both minerals is of greater significance than the ratio. Résumé Les relations métaboliques entre le Calcium et le Phosphore ont étéétudiées lors d'une série d'expèriences sur des poneys et de jeunes chevaux. Des taux croissants de Calcium variant de 0,15%à 1,5% de la ration ont eu peu d'effet sur le métabolisme du Phosphore quand le taux du Phosphore était compris entre 0,35 et 0,4% de la ration. Le Phosphore unrinaire diminuait quand le taux de Calcium ingèré augmentait, peut etre parce que plus de Phosphore était utilisé dans l'élaboration du tissu osseux. Un régime élevé en Phosphore (1,2% de la ration), avec 0,4% de Calcium, pour un rapport Ca:P de 0,3:1, s'accompagnait d'une réduction de l'absorbtion intestinale et de la rétention du Calcium. Le taux plasmatique de Calcium diminuait, le taux plasmatique de Phosphore augmentait. Les remaniements osseux, mesurés d'après le rythme de dépot puis de retrait du Calcium, furent accèlèrés. Ces résultats furent attribués plus au taux élevé de Phosphore dans le régime qu'à la valeur du rapport phospho calcique. Des poneys nourris d'un régime analogue par ses constituants, pour un rapport Ca:P de 0,4:1 mais déséquilibré en Calcium, absorbèrent le Calcium suivant un bon rendement. Les taux de Calcium et de Phosphore dans le plasma sanguin, et le taux de depot du Calcium sur le tissu osseux ne furent pas affectés par ce régime. Par contre, le taux de retrait du Calcium osseux fut accru, en réponse à ce régime pauvre en Calcium. L'addition de Phosphore sous forme de Phosphate inorganic ou de phytate de Sodium (0,6 à 0,8%) à une ration suffisante en Calcium (0,43%) parut inhiber l'absorbtion du Calcium mais n'affecta point la concentration du Phosphore ni celle du Calcium dans le plasma sanguin. Les effets du Phosphore ajouté sous forme de phytate de sodium furent comparable à ceux du Phosphore ajouté sous forme de Phosphate inorganique. Le rapport Ca:P devrait etre supèrieur à l'unité mais d'autres recherches sont nécessaires pour définir ce rapport plus précisèment. Cependant les quantités absolues des deux minéraux ont plus d'importance que le rapport lui meme. Zusammenfassung Die Beziehungen zwischen Ca und P wurden in einer Serie von Experimenten an jungen Pferden und Ponies studiert. Abgestufte Calciumgaben von 0,15 bis 1,5% beeinflussten den Phosphormetabolismus kaum, wenn die Phosphorkonzentration 0,35 bis 0,4% der Diät ausmachte. Der P-Gehalt des Harns nahm ab, wenn die Ca-Aufnahme gesteigert wurde, möglicherweise weil mehr P für die Knochenbildung gebraucht wurde. Eine reichliche P-Diät (1,2%), mit genügend Ca (0,4%) und einem Ca:P-Verhältnis von 0,3:1 führte zu abnehmender Ca-Darmresorption und -retention. Der Ca-Gehalt des Plasmas nahm ab und die Plasmakonzentration von P stieg an. Der Knochenumsatz, gemessen an der Ablagerungsrate und der Entfernung von Knochen-Ca war beschleunigt. Die Resultate dürften eher dem hohen P-Gehalt der Diät als dem Ca:P-Verhältnis zuzuschreiben sein. Ponies, die eine ähnliche Diät mit einem Ca:P-Verhältnis von 0,4:1 und ungenügendem Ca-Angebot (0,15%) erhielten, absorbierten Ca sehr wirkungsvoll. Plasma-Ca und -P und die Ablagerungsrate von Ca im Knochen blieben unverändert. Hingegen erwies sich die Verlustrate von Knochen-Ca als erhöht bei der Ca-armen Diät. Phosphorzusätze als anorganischer P oder Na-Phytat (0,6 bis 0,8%) zu einer adaequaten Ca-Diät (0,43%) schienen die Ca-Absorption zu hemmen, allerdings ohne die Plasma-Konzentrationen von Ca oder P zu beeinflussen, wobei die Wirkung von P als Na-Phytat derjenigen des anorganischen Phosphors ähnlich war. Das Ca:P-Verhältnis sollte grösser sein als 1, aber weitere Untersuchungen über dieses Verhältnis sind notwendig. Immerhin ist die absolute Aufnahme beider Mineralien entscheidender als ihr Verhältnis zueinander. [ABSTRACT FROM AUTHOR]