Effect of controlled exercise on middle gluteal muscle fibre composition in Thoroughbred foals

REASONS FOR PERFORMING STUDY: Most racehorses are trained regularly from about age 18 months; therefore, little information is available on the effect of training in Thoroughbred foals. HYPOTHESIS: Well-controlled exercise could improve muscle potential ability for endurance running. METHODS: Thoroughbred foals at age 2 months were separated into control and training (treadmill exercise) groups and samples obtained from the middle gluteal muscle at 2 and 12 months post partum. Muscle fibre compositions were determined by histochemical and electrophoretical techniques and succinic dehydrogenase (SDH) activity was analysed in each fibre type. RESULTS: All fibre types were hypertrophied with growth and type I and IIA fibres were significantly larger in the training than the control group at age 12 months. A significant increase of SDH activity was found in type IIX muscle fibres in the training group. CONCLUSIONS: Training in young Thoroughbred horses can facilitate muscle fibre hypertrophy and increase the oxidative capacity of type IIX fibres, which could potentially enhance stamina at high speeds. POTENTIAL RELEVANCE: To apply this result to practical training, further studies are needed to determine more effective and safe intensities of controlled exercise.     

Arterial blood gas tensions during exercise in a horse with laryngeal hemiplegia, before and after corrective surgery

Arterial blood samples were collected during maximal exercise over 1.6 km in a thoroughbred horse with left laryngeal hemiplegia. Acid-base and blood gas measurements were performed on each sample and compared to the results from samples which were similarly collected 48 hours after laryngoplasty surgery was performed. Before surgery, the PaO2 was 53.2 mm Hg and the PaCO2 was 58.1 mm Hg after 1.6 km. After surgery, the corresponding results were 83.6 mm Hg (PaO2) and 39.0 mm Hg (PaCO2). There was no significant difference in the times taken for each gallop. The exercise intolerance associated with laryngeal paralysis may be caused by an increase in the oxygen cost of breathing.     

Early exercise in the horse

Across all equestrian disciplines, the single largest reason for wastage is musculoskeletal injury. It is, therefore, of importance that management and competition structures are in place to optimize the development of the equine musculoskeletal system to minimize wastage.Data from other species and, in particular, humans have demonstrated the benefit of early exercise and the dire consequences of inactivity. The horse has evolved as a cursorial animal capable of covering up to 10 km/d within 9 days of birth. Yet, modern equine management systems restrict, rather than promote, early exercise. Foals were shown to have a positive response to early preweaning paddock exercise (greater cartilage health), and more recent work has demonstrated that exercise over and above that normally occurring with pasture-reared foals, introduced as early as 3 weeks old, had positive effects on the equine musculoskeletal system. The response of juvenile horses to additional exercise is because of the tissue being responsive to priming. Epidemiological data indicate that the window for tissue modification may still be open when the horse is a yearling and even as a 2 year old.However, the method in which the exercise is applied may be of as much importance as the timing of the stimuli. A recent prospective study of both Thoroughbred and Standardbred horses demonstrated that the horses that entered training as 2 year olds had longer and more successful racing careers than those that entered training later in life. It would appear that even the initial stages of training are enough to provide a positive stimulus, as horses first registered with a trainer at 2 years old had the same advantages as those that raced as 2 year olds.The physiological, clinical, and epidemiological data indicate that, rather than restrict exercise and the use of horses at a young age, we should realign expectations with the capability of the horses’ musculoskeletal system and evolutionary template to maximize orthopedic health.     

Amino acid profile during exercise and training in Standardbreds

The objective of this study is to assess the influence of acute exercise, training and intensified training on the plasma amino acid profile.In a 32-week longitudinal study using 10 Standardbred horses, training was divided into four phases, including a phase of intensified training for five horses. At the end of each phase, a standardized exercise test, SET, was performed. Plasma amino acid concentrations before and after each SET were measured.Training significantly reduced mean plasma aspartic acid concentration, whereas exercise significantly increased the plasma concentrations of alanine, taurine, methionine, leucine, tyrosine and phenylalanine and reduced the plasma concentrations of glycine, ornithine, glutamine, citrulline and serine. Normally and intensified trained horses differed not significantly. It is concluded that amino acids should not be regarded as limiting training performance in Standardbreds except for aspartic acid which is the most likely candidate for supplementation.     

Branched‐chain amino acid ratios in low‐protein diets regulate the free amino acid profile and the expression of hepatic fatty acid metabolism‐related genes in growing pigs

Liver metabolism is affected by nutrients. The aim of this study was to explore the effects of low‐protein diets (17% crude protein, CP) supplemented with branched‐chain amino acids (BCAAs), including leucine (Leu), isoleucine (Ile) and valine (Val), on hepatic amino acid profile and lipid metabolism in growing pigs. The ratio of Leu : Ile : Val in all groups was 1 : 0.51 : 0.63 (20% crude protein, CP), 1 : 1 : 1 (17% CP), 1 : 0.75 : 0.75 (17% CP), 1 : 0.51 : 0.63 (17% CP) and 1 : 0.25 : 0.25 (17% CP) respectively. Results revealed that compared to the positive control group (1 : 0.51 : 0.63, 20% CP), the low‐protein diets significantly augmented the concentrations of most essential amino acids and non‐essential amino acids (p < .05), with the greatest values observed in the 1 : 0.25 : 0.25 group. Moreover, relative to the control, the low‐protein diets with the Leu : Ile : Val ratio ranging from 1 : 0.75 : 0.75 to 1 : 0.25 : 0.25 markedly downregulated the mRNA abundance of acetyl‐CoA carboxylase (ACC), lipoprotein lipase (LPL) and fatty acid‐binding protein 4 (FABP‐4) (p < .05), and upregulated the mRNA expression of hormone‐sensitive lipase (HSL), peroxisome proliferator‐activated receptor‐g coactivator‐1α (PGC‐1α), uncoupling protein 3 (UCP3) and liver carnitine palmitoyltransferase 1 (L‐CPT‐1) (p < .05). Therefore, our data suggest that protein‐restricted diets supplemented with optimal BCAA ratio, that is, 1 : 0.75 : 0.75–1 : 0.25 : 0.25, induce a shift from fatty acid synthesis to fatty acid oxidation in the liver of growing pigs. These effects may be associated with increased mitochondrial biogenesis.     

The effects of short intensive exercise on plasma free amino acids in standardbred trotters

The aim of this study was to investigate the effect of short intense exercise on plasma amino acid concentrations in trotters and to test the repeatability of plasma amino acids concentration in samples obtained on two independent days under field conditions. Plasma amino acid concentrations were analysed in blood samples of 36 standardbred trotters before and after intense exercise over a distance of 2000 m. Sampling was repeated in 20 horses after 35 days. Exercise intensity was estimated from post‐exercise lactate levels. Horses were divided in two groups according to a cut‐off lactate concentration at 15 mmol/l. The plasma concentrations of alanine, aspartate, glutamate, isoleucine, leucine, lysine and taurine increased and arginine, asparagine, citrulline, glutamine, glycine, histidine, methionine, serine, tryptophan and 3‐methylhistidine decreased after exercise. Ornithine, threonine, tyrosine, phenylalanine and valine concentrations remained constant. Higher intensity of exercise significantly decreased tryptophan and increased taurine concentrations. Sampling day had a significant effect on the absolute pre‐ and post‐exercise amino acid concentrations. Exercise had a significant influence on the concentrations of most plasma amino acids in trotters. These changes could reflect shifts between the free amino acid compartments, but there were also some indications for muscle catabolism. The amino acid supply of sporting horses could be of specific significance for maintaining muscle integrity and for the improvement of post‐exercise recovery of competition horses.     

Respiratory responses to exercise in the horse

Horses are elite athletes when compared with other mammalian species. In the latter, performance is limited by cardiovascular or musculoskeletal performance whereas in athletic horses it is the respiratory system that appears to be rate limiting and virtually all horses exercising at high intensities become hypoxaemic and hypercapnoeic. This is due to both diffusion limitation and a level of ventilation inadequate for the metabolic level that enables horses to exercise at these intensities. In conjunction with these blood gas changes, total pulmonary resistance increases and the work of breathing rises exponentially and airflow eventually plateaus despite increases in inspiratory and expiratory intrapleural pressures. Horses breathe at comparatively high frequencies when galloping due to the tight 1:1 coupling of strides to breathing. Whether this effects gas exchange and, if so, to what extent, has not been fully elucidated.     

动物营养代谢中的酸碱平衡

动物维持正常的酸碱平衡,是发挥机体细胞整体功能效应的必要前提。当某种酶活性对微小ｐＨ值变化敏感时,许多中间代谢产物反应,调控着动物细胞酸碱平衡。酸碱平衡是氢离子浓度的一种功能。当难于测定细胞内液和亚细胞内ｐＨ变化时,一般测定细胞外液中氢离子浓度,大多数哺乳动物细胞外液氢离子浓度维持在低水平状态(40×10-9ｍｏｌ/Ｌ或40ｎＥｑ/Ｌ,ｐＨ74)。细胞内液氢离子浓度比细胞外液高,哺乳动物肌肉细胞胞液ｐＨ值67～71变化,这种差异是维持细胞内代谢产物浓度的重要因子。但在细胞内,亚细胞器与胞液间也存在氢离子浓度差异。线粒体内…     

The pharmacokinetics of meclofenamic acid in the horse

The pharmacokinetics of meclofenamic acid were studied in Thoroughbred horses and in ponies. After intravenous (i.v.) administration of either 2 mg/kg or 4 mg/kg sodium meclofenamate the elimination half-life was of the order of 0.9 h while the volume of distribution was found to be 0.128 litre/kg. Elimination was in accordance with a one-compartment model. Following oral administration of either meclofenamic acid (4 mg/kg) or sodium meclofenamate (4 mg/kg) a much longer terminal half-life than that calculated for K _el from i.v. data was found. This anomaly indicated that the 'flip-flop' phenomenon was present, i.e. K _a exceeded K _el. More rapid and higher peak levels occurred following sodium meclofenamate than meclofenamic acid, although total bioavailability was similar. Studies in ponies with meclofenamic acid showed a lower absorption than that found in Thoroughbreds. Overnight fasting before meclofenamic acid administration did not alter the rate or extent of absorption. Intramuscular administration of sodium meclofenamate resulted in low plasma concentrations and after 25 h only 46% of the drug had been absorbed.     

Osteosarcoma of the middle phalanx in a horse

An 11‐year‐old Thoroughbred gelding was presented for lameness investigation following acute onset hindlimb lameness, which developed during a period of paddock turnout. Clinical examination revealed a swelling over the dorsolateral aspect of the pastern that was painful on digital palpation. Radiography of this area was consistent with an aggressive bone lesion involving both joint surfaces of the middle phalanx with pathological fracture and distal collapse of this bone. On this basis, the horse was subjected to euthanasia. Post mortem histopathological examination revealed presence of an osteosarcoma without involvement of the articular cartilage. This bone tumour is extremely rare in horses and has not been reported in this anatomical location.     

Influences of dietary protein sources and crude protein levels on intracellular free amino acid profile in the longissimus dorsi muscle of finishing gilts

Background: The current study was carried out to determine effects of dietary protein source and crude protein(CP)level on carcass characteristics, meat quality, and muscle amino acid(AA) profile in finishing gilts. The experiment was designed as a 2 × 2 factorial arrangement with two sources of dietary proteins(cottonseed meal, CSM vs. soybean meal, SBM) and two levels of CP(12 % vs. 14 %, as-fed basis). Seventy-two crossbred gilts(89.5 ± 0.9 kg) were allotted to one of four dietary treatments in a randomized complete block design for a period of 28 d. All diets were formulated to be isoenergetic and similar concentrations of standardized ileal digestible essential AA covering the nutrient requirements of pigs.Results: Growth, carcass characteristics and meat quality were not affected by dietary protein source nor crude protein level(P 0.10) except that average daily feed intake was increased by CSM diets(P = 0.03). Gilts offered reduced protein diets had lower muscle p H45min(P 0.05). Neither dietary protein source nor crude protein level influenced N deposition. However, reduced protein diets decreased N intake, N excretion, and serum urea nitrogen content, whilst improved N efficiency(P 0.01). CSM diets increased N intake(P = 0.04),but did not depress N efficiency. The concentrations of phenylalanine, tryptophan, cysteine and tyrosine(P 0.05) of the longissimus muscle were decreased when gilts offered CSM diets, while muscle intracellular free valine concentration was increased(P = 0.03). The gilts offered reduced protein diets had greater intracellular concentrations of free methionine, lysine, and total AA in muscle(P 0.05).Conclusion: These results suggest that CSM could replace SBM as a primary protein source in finishing pig diets in terms of performance, N efficiency, carcass characteristics, and meat quality, but decrease the concentrations of muscle specific AA. Furthermore, the reduced protein diet played an important role in increasing muscle intracellular concentrations of specific free amino acids(FAA), and in reducing the relative ratios of specific FAA to lysine in longissimus dorsi muscle of pig, whose biological meaning needs further studies.     

Cardiovascular response to exercise and training in the horse

The quality of the overall response to exercise in the horse is very similar to that seen in man and laboratory animals; differences are mainly quantitative and persist when relative body weight is taken into account. The apparently greater flow capacity of the equine muscle bed during maximal whole-body exercise implicates the extent of central circulatory adaptations as the limiting factor in performance but implies a role for increase in arteriolar capacitance/muscle capillarity as an appropriate response to intense endurance training. The blood oxygen-carrying capacity of the horse is often quoted as the major component of the animal's superior aerobic work capacity, although the measured maximal a-vO2 for the horse is only 2 to 3 ml greater than that found in elite athletes. In fact, comparison of published performance data for man and the horse reveals that improved a-vO2 accounts for 23 per cent of the difference, and increased Qc accounts for the remaining 77 per cent of the superior oxygen consumption in the horse. The extent to which the horse can increase Qc and muscle blood flow appears to represent its major adaptations for maximal aerobic performance. It is frequently observed that there have been far greater improvements in human athletic performance than in that of the race-horse, and this difference is usually attributed to the application of scientific training methods to the athlete. It has also been suggested that the horse may have reached the limit of its adaptive ability. The horse has a maximal oxygen pulse of at least 0.6 ml per kg per beat compared with 0.35 for man, a 90 per cent whole body oxygen extraction, and an 80 to 90 per cent higher muscle blood flow, with an overall capability of increasing Vo2 max by 35 times. These represent levels that would appear to be difficult to improve upon. However, insufficient research has been performed to firmly state true maxima for the horse, and current research does not reveal to what extent the horse is capable of responding to even conventional training methods. The relative improvement that such research could reveal would provide some objective guidance to the extent to which further improvement could be anticipated. A consistent finding in the majority of studies reviewed is the tendency for results to show a lack of statistical significance, which is particularly frustrating for a researcher when the trends are consistent with the initial hypotheses. This tendency arises because of small group sizes and inherent variability in the test population.(ABSTRACT TRUNCATED AT 400 WORDS)     

Resting concentrations of the plasma free amino acids in horses following chronic submaximal exercise training

Six horses were conditioned on a treadmill at a constant speed of 5.6 km/hr on a 12.5% grade for gradually increasing periods of time over 14 days in order to determine the effect of repeated submaximal exercise on the concentrations of plasma free amino acids, protein metabolism, and plasma volume. Following 14-days of training, plasma volume increased (29%, P<0.05), as did total circulating content of plasma protein, albumin and urea. Urinary urea nitrogen excretion decreased (P<0.05) with exercise training. After the first week of training, the concentration of glycine had decreased (P<0.05) and the concentrations glutamic acid, arginine and alanine were increased (P<0.05) when compared to their corresponding pre-training (control week) levels. Compared to pretraining levels, there were decreases (P<0.05) in aspartic acid, histidine, arginine, valine, phenylalanine, isoleucine, and lysine, following the second week of training. Following a week of recovery, all resting concentrations of plasma free amino acids; when compared to their pretraining control; had decreased, with the exception of three nonessential amino acids (glutamic acid,serine, and glycine). Based upon the results of the present study, it would appear that exercise training produced a significant change in the amino acid and protein metabolism of the horse.     

Total carnitine content of the middle gluteal muscle of thoroughbred horses: normal values, variability and effect of acute exercise.

There was no detectable loss of total carnitine associated with intense exercise from the middle gluteal muscle of Thoroughbred horses. Measurements made on a single biopsy obtained during the course of a normal training and exercise programme may, therefore, be considered representative of the normal content at rest. The variability in total carnitine content within the normal muscle biopsy area amounted to 13.2 per cent of the normal mean content. Approximately 50 per cent of this variability could be attributed to covariation with citrate synthase, to which it was highly significantly correlated. The muscle carnitine content of yearling Thoroughbred horses ranged from 10.5 to 18.8 mmol/kg dry muscle (dm); the ranges in untrained, lightly trained and fully trained two-year-olds were 18.5 to 34.7, 14.1 to 24.2 and 22.9 to 26.9 mmol/kg dm, respectively. In horses aged over three years total carnitine ranged from 21.3 to 35.5 mmol/kg dm. A trend toward higher contents of total carnitine with age and training appeared to be largely a consequence of underlying changes in mitochondria density as indicated by differences in levels of citrate synthase activity. There was a marked difference in ratios of total carnitine to citrate synthase activity between training yards, reflecting possible differences in management regimens and/or bloodstock selection.