Long-term effects of endurance training on total tract apparent digestibility, total mean retention time and faecal microbial ecosystem in competing Arabian horses

International audienceIn endurance horses, commonly fed 80% forage, energy is provided mainly by VFA produced in the hindgut during cell wall degradation, but cell wall digestibility has been reported to be impaired by exercise. To assess the influence of a long-term endurance conditioning on cell wall digestion in horses. The total tract apparent digestibility of dry matter, organic matter and fibrous constituents, solid and liquid total mean retention time and the faecal microbial ecosystem of purebred Arabian horses were measured for 2 years in 2 longitudinal experiments. Performed at the beginning of each year for control level and after conditioning periods corresponding to incremental endurance racing levels: 60, 90 (year 1) and 120 (year 2) km. During the 5 measurement periods, feed intake and diet composition were similar. In year 1, digestibility of DM, OM and NDF was higher after 10 weeks of training (P = 0.008, P = 0.010 and P = 0.031, respectively), corresponding to the 90 km level, compared to the pretraining level. In year 2, NDFd and (NDF-ADF)d tended to be higher (P = 0.06 and P = 0.07, respectively) after the 17 weeks conditioning necessary to reach 120 km level, than before training. These variations were not systematically associated to a longer total MRT, neither to an increase in the microbial fibrolytic activity. Digestibility of DM, OM and NDF appeared to be higher after endurance conditioning. Such an increase could be beneficial for endurance horses as it would provide more energy from forage degradation. Additional experiments are needed to elucidate the mechanisms, understand some contradictory results and investigate methodological aspects

Physiology of intake and digestion in Equine animals

This review focuses on some recent advances in our understanding of the physiological mechanisms involved in intake and digestion. Different factors, either intrinsic or external to the individual, which can impact the intake and digestion of feeds are discussed with a special focus on the effect of feeding practices and exercise of sport and race horses so far removed from their natural environment. Exercise probably has an impact on the physiology of intake and digestion but it is not well documented mainly due to methodological limits. The motivation of a horse for ingesting a feedstuff is strongly influenced by the feed palatability (related to the smell, taste, appearance or texture). Feed intake integrates probably the nutritive value of a feed as well as its hedonic value or its aversion value. There is also large individual variation that should be taken into account when feeding different horses. It seems that gastric or cecal repletion had no effect on subsequent feeding behaviour. Feed intake is regulated on a short term by glucose and acetate and by leptin and ghrelin hormones and on a long term by the nutritional needs of the organism, which are modified by on the physiological status, activity and thermoregulation. Regarding the implication on energetic yield, digestion in horses shall be studied in the various compartments of the digestive tract. Most studies are conducted on apparent digestibility and mean retention time in the total gastro-intestinal tract which limits the comprehension of partial digestibility. Digestion of starch starts in the stomach with enzymes from the host and originated from abundant autochthonous microorganisms. In the small intestine, digestion is primarily under the control of the host enzymatic secretions that breakdown carbohydrates, fat and protein. Microbial cell-walls degradation occurs in the favourable ecosystem of the hindgut.vo

Effect of a 120 km endurance race on plasma and muscular neutrophil elastase and myeloperoxidase concentrations in horses.

peer reviewedREASONS FOR PERFORMING STUDY: Intense physical exercise can induce the degranulation of neutrophils leading to an increase in plasma concentration of the neutrophil marker enzymes myeloperoxidase (MPO) and elastase (ELT). These enzymes have pro-oxidative and pro-inflammatory properties and may play a role in the exercised-induced muscular damage. OBJECTIVES: To measure MPO and ELT concentrations in plasma and muscles of endurance horses and to correlate them to the extent of exercise-induced muscular damage. METHODS: Seven endurance horses qualified on 120 km races were tested in this study. Neutrophil count, serum creatine kinase (CK), plasmatic and muscular MPO and ELT concentrations were measured before and 2 h after a 120 km endurance race. RESULTS: The race produced a significant increase of neutrophils, CK, and plasma MPO and ELT levels. A significant correlation was observed between the MPO and ELT values in plasma (r(2) = 0.92, P < 0.01) and in muscles (r(2) = 0.89, P < 0.01) while plasmatic concentrations of MPO and ELT were not significantly correlated to muscular ones. An increase of mean concentrations (± s.e.) of MPO (T0: 9.85 ± 3.9, T1: 228.9 ± 95.9 ng/mg proteins) and ELT (T0: 8.4 ± 2.4, T1: 74.5 ± 39.7 ng/mg proteins) in the muscles were observed after the race. Interestingly, the individual data showed large differences between the horses. Muscular MPO and ELT concentrations were significantly correlated to plasma CK levels. The coefficient of correlation (r(2)) was 0.69 (P < 0.01) for MPO and 0.66 (P < 0.01) for ELT, respectively. CONCLUSIONS: Results underline the possible role of MPO and ELT in exercise-induced muscular damage. POTENTIAL RELEVANCE: Further studies should investigate the effect of exercise type and intensity, as well as the role of the training state on MPO and ELT involvement in muscular damage. The assessment of the intensity of exercise-induced neutrophilic degranulation may have a potential role in the monitoring of the athletic career