This study was undertaken as part of a larger investigation into carnosine metabolism and function in the Thoroughbred horse. More specifically, we wished to evaluate plasma carnosine concentration as a potential indicator of muscle carnosine status. In contrast to man, carnosine is present in equine plasma where its presence is consistent with the absence of plasma carnosinase. A significant effect of age on plasma carnosine concentration in resting Thoroughbred horses was observed. Values in horses age 3 years and older were 113-14.1 micromol/l, whereas concentrations in foals and yearlings were 3.9-8.7 micromol/l (P<0.001). Lower values in young horses may reflect lower skeletal muscle carnosine concentrations. There was no significant within-day variation in plasma carnosine concentration in fed and fasted horses (P>0.05). Intense exercise resulted in a small significant increase (P<0.05) in plasma carnosine concentration (pre-exercise, 10.3 +/- 1.0 micromol/l; postexercise, 12.4 +/- 4.4 micromol/l). Greater increases were observed (57.6-702.3 micromol/l) following onset of exercise-induced rhadomyolysis (ERS). An apparent relationship was observed between elevated plasma carnosine and increased plasma creatine kinase (CK) and aspartate transaminase (AST) activities. Plasma carnosine concentrations did not reflect the severity of the condition as determined by clinical examination. In conclusion, elevated plasma carnosine levels are observed following exercise induced muscle damage, with the greatest elevations occurring during episodes of external rhabdomylosis syndrome. Plasma carnosine measurements could provide an alternative clinical indicator of muscle damage; and in conjunction with plasma taurine measurements may be indicative of selective type 1 or type 2 muscle fibre damage. However, given the complexity of the analytical technique, its applications would probably be confined to specialist referral or research centres.

The aim of the present study was to relate changes in muscle oxidative capacity and free fatty acid flux in response to oil supplementation to fuel utilisation during subsequent exercise of varying intensities. Following 10 weeks of oil supplementation there was an increased capacity for fat utilisation during low and moderate intensity exercise as indicated by a lower respiratory exchange ratio (RER) (P<0.05). We suggest that this was contributed to by a parallel increase in the oxidative capacity of muscle as indicated by a significant increase in the activity of muscle citrate synthase (CS) (P<0.05) and trend towards an increase in beta-Hydroxy acyl CoA dehydrogenase (beta-HAD), (P>0.05). In addition, low and moderate intensity exercise was associated with an exercise-induced increase in plasma free fatty acids (FFA) and there was an increased facility for uptake of FFA by working muscle from circulating triglycerides, as suggested by an increase in TL activity (P<0.01). The response to oil supplementation varied between individual horses and the magnitude of response, during the low intensity exercise test, in terms of difference in RER was correlated to the increase in CS activity (r2 = 0.95, P<0.05) following oil supplementation. There was no similar significant correlation with respect to FFA, TL or beta-HAD activity (P>0.05). The hypothesis in this study was that the metabolic adaptation to oil supplementation, in terms of exercise response, was related to individual increases in the activities of CS, beta-HAD or TL. However, the relationship between these parameters was unequivocal and requires further investigation, ideally with a larger group of horses.

Mare BCS correlated with foal birthweight; obese mares had heavier foals. Significant hyperinsulinaemia was not identified in this population. Increased leptin concentration in early and late gestation was associated with decreased foal birthweight. Further work is required to establish whether leptin concentration in late gestation could predict foal birthweight.

Summary As a herd‐living, nonruminant, hindgut fermenting, primarily grazing herbivore the horse has evolved with a specialised gastrointestinal tract capable of utilising a wide range of plant species, which are hydrolysed and/or fermented to yield energy and nutrients for bodily processes. Domestication has resulted in the horse often being fed and managed to suit human requirements rather than their own, which can lead to digestive, behavioural and clinical issues. Appropriate nutrition not only reduces the risk of a nutritional component being a limiting factor to performance, but it also supports the maintenance of health and appropriate behaviour. A basic understanding of the digestive processes therefore can be very valuable when deciding how to feed horses optimally for both health and activity. This article provides a general overview of the gastrointestinal tract from a nutritional perspective and points out a few key practical areas where knowledge of feeding practices can be helpful for veterinarians.

A series of experiments was conducted to determine the effects of a fibrolytic enzyme preparation (enzyme 1; E1) on the in vitro fermentation of lucerne incubated with equine faecal inocula. In experiment 1, high-temperature-dried (HT) lucerne was treated with five levels of E1 (0 to 2·4 ml/g DM) and incubated at 508C for 20 h. Samples then received a simulated foregut digestion (SFD) treatment before DM and NSP analysis. In experiment 2, HT lucerne was treated with the same enzyme levels used in experiment 1. Samples were then split into two groups; plus or minus an SFD treatment before in vitro fermentation using an equine faecal inoculum. In experiment 3, fresh and wilted lucerne were treated with the same levels of E1 as experiments 1 and 2, incubated at 508C for 20 h, then fermented in vitro. For experiment 4, fresh and wilted lucerne were treated with low levels (0 to 0·008 ml/g DM) of E1 before fermentation. E1 significantly (P,0·05) enhanced DM and NSP losses from HT lucerne following SFD treatment compared with the control. High levels of E1 significantly (P,0·05) enhanced the rate, but not extent, of fermentation of HT, wilted and fresh lucerne; however, low levels of E1 were ineffective. At higher application levels, E1 appears to have considerable potential to enhance the nutritive value of lucerne for horses. Information on the fermentation kinetics of the substrates was valuable; all end-point measurements showed no effect of enzyme treatment. Enzyme treatment: In vitro fermentation: Equine inocula: LucerneThere is increasing interest in feeding high-energy, fibre-based feeds as an alternative to feeding cereal grains as a means of meeting the energy demands of working horses. This is due to the association of the onset of metabolic disorders, such as laminitis and colic, with feeding high levels of cereal grains. Preparations of fibrolytic enzymes have the potential to initiate the hydrolysis of forage fibre (structural carbohydrates), rendering the fibrous fraction more amenable to degradation in vivo. Exogenous fibrolytic enzymes have been reported to enhance the nutritive value of forages fed to ruminants by enhancing the digestibility of plant structural carbohydrates, thus enhancing the overall energy balance in the animal (Beauchemin et al.