Effects of training distance on feed intake, growth, body condition and muscle glycogen content in young Standardbred horses fed a forage-only diet.

This study examined feed intake, growth, body condition, muscle glycogen content and nutrition-related health in 16 Standardbred horses fed a high-energy, forage-only diet ad libitum and allocated to either a control training programme (C-group) or a training programme with the high-intensity training distance reduced by 30% (R-group), from January as 2-year olds until December as 3-year olds. Feed intake was recorded on 10 occasions during 3 consecutive days. Body weight was recorded once in a week and height, body condition score (BCS), rump fat thickness and thickness of the m. longissimus dorsi were measured at 7±3-week intervals throughout the study. Muscle biopsies of the m. gluteus medius were taken in December as 2-year olds and in November as 3-year olds and analysed for glycogen content. Nutrition-related health disorders were noted when they occurred. Horses consumed 1.7% to 2.6% dry matter of BW, corresponding to 19 to 28 MJ metabolisable energy/100 kg BW. There were no differences between training groups in feed intake or any of the body measurements. The pooled weekly BCS was maintained between 4.8 and 5.1 (root mean square error (RMSE)=0.4). Muscle glycogen content was 587 and 623 mmol/kg dry weight (RMSE=68) as 2- and 3-year olds, respectively, and there was no difference between training groups. When managed under normal conditions, no nutrition-related health disorders or stereotypic behaviours were observed. It was concluded that the training programme did not affect feed intake, growth, BCS or muscle glycogen content. In addition, the forage-only diet did not appear to prohibit muscle glycogen storage, growth or maintenance of body condition, and seemed to promote good nutrition-related health.

Histopathological assessment of intrinsic laryngeal musculature in horses with dynamic laryngeal collapse.

REASONS FOR PERFORMING STUDY: The pathogenesis of bilateral dynamic laryngeal collapse associated with poll flexion (DLC) of horses is unknown but might be associated with intrinsic laryngeal muscle weakness. OBJECTIVES: To investigate histopathological characteristics of the cricoarytenoideus dorsalis, the cricothyroid (CT) and the cricoarytenoideus lateralis muscles in DLC-affected horses and compare these with unaffected controls. Our hypotheses were that evidence of neurogenic atrophy of the CT or cricoarytenoideus dorsalis muscles would be found in DLC-affected horses and that observed changes would be symmetrically (left/right) distributed, or that muscle fibre diameter would be significantly reduced in DLC-affected horses compared to unaffected controls, reflecting an underlying paresis. STUDY DESIGN: Case-control study. METHODS: Five DLC horses and 8 controls were included. Muscle samples were harvested immediately following euthanasia. Fibre type proportions and size were evaluated by multiple immunofluorescence labelling of cryosections, and compared between sides (left/right) and groups (DLC-affected cases/ unaffected controls). Subjective and objective assessments of fibre type grouping were compared between sides and groups. RESULTS: Fibre type proportions, fibre size and the subjective assessment of fibre type grouping did not reveal any statistically significant differences between the groups. Objective assessment of fibre type grouping revealed significantly more large clusters of T1 fibres within the left cricoarytenoideus lateralis muscle of DLC-affected cases versus controls, and within the right CT muscle of control horses compared to the DLC-cases. CONCLUSIONS: The absence of bilateral symmetric fibre type grouping, fibre type loss and fibre atrophy in the DLC-affected cases do not support a neuromuscular component within the pathogenesis of DLC. The objective assessment of fibre type grouping revealed some statistical differences between the DLC-affected cases and the unaffected controls; however, these findings were inconsistent with regard to DLC. An alternative aetiology of DLC seems likely.

Growth, training response and health in Standardbred yearlings fed a forage-only diet.

The aim of this study was to, from a holistic perspective, describe the effects of a forage-only feeding system and a conventional training program on young Standardbred horses and compare data with similar observations from the literature. Sixteen Standardbred colts fed a forage-only diet for 4 months from breaking (August to December) and with the goal to vigorously trot 5 to 7 km at a speed of 5.6 m/s (3 min/km) were studied. The horses were fed grass haylage (56 to 61% dry matter (DM), 2.80 to 3.02 Mcal DE/kg DM and 130 to 152 g CP/kg DM) ad libitum, 1 kg of a lucerne product and minerals. The amount of training and number of training sessions were documented daily, and feed intake and body development were measured once every month. Heart rate (HR) was measured during and after a standardized exercise test in October and December. In December, a postexercise venous blood sample was collected and analyzed for plasma lactate concentration. Muscle biopsies (m. gluteus medius) were taken and analyzed for glycogen and fiber composition. Health was assessed in October and November by an independent veterinarian using a standardized health scoring protocol. BW and height at withers increased from 402 to 453 kg (root mean square error (RMSE) 6) and from 148.7 to 154.1 cm (RMSE 0.7), respectively, and the body condition score was 4.9 (RMSE 0.2) at the end of the study. Muscle glycogen content was 532 mmol/kg dry weight (s.d. 56). There was a significant decrease in postexercise HR (81 v. 73 bpm, RMSE 8), and the individual amount of training was negatively correlated with HR during and after exercise. Health scores were high and similar at both assessments (8.4 and 8.4 (RMSE 1.0) out of 10; P > 0.05), and the number of lost training days per month due to health problems was <0.9, with the exception of November (5.3 days). It is concluded that yearlings in training fed high-energy forage ad libitum can reach a conventional training goal and grow at least as well as earlier observations on yearlings of other light breeds.

Muscle characteristics in young Norwegian-Swedish Coldblooded Trotters and associations with breeding index, body size and early training.

REASONS FOR PERFORMING STUDY: The trotting speed of Norwegian-Swedish Coldblooded Trotters (NSCTs) is, although inferior to Standardbred speeds, gradually increasing. This development is mainly attributed to breeding progresses. Characteristics of the middle gluteal muscle have recently been described in a small number of these horses but the actual spread in muscle parameters within the population is unknown. OBJECTIVES: To describe the characteristics of the middle gluteal muscle and their naturally occurring variability in young NSCT horses and investigate possible association with body size, individual breeding index and early training. METHODS: Biopsies of the middle gluteal muscle of 144 NSCT horses born in 2005 were collected at age 17-24 months. The horses were randomly selected by stratified sampling with gender and paternal progeny as stratification factors. The muscle samples were analysed for fibre type composition, fibre type areas, capillary supply and the activity of the key metabolic enzymes citrate synthase, 3-OH-acyl-CoA-dehydrogenase and lactate dehydrogenase. Correlation analysis including muscle parameters and body size, individual breeding index and early training was performed. RESULTS: Large interindividual differences were identified in muscle characteristics. Male horses had higher percentages of type IIA fibres and lower percentages of type IIX fibres than age-matched females. Fibre type areas followed the order type IIX>IIAX>IIA>I, while the capillary supply per fibre type area increased in the opposite order. No gender-related differences were found in fibre type areas or capillary supply. Height was correlated to the relative area of type I fibres. Early training was associated with increased oxidative capacity and increased percentage of type IIA fibres. The lowest breeding index was found in untrained horses. CONCLUSIONS: Muscle characteristics differ among young NSCT horses, but the innate oxidative capacity seems to be lower than in Standardbreds of comparable age. Early training may influence on these parameters.

Effects of training on equine muscle fibres and monocarboxylate transporters in young Coldblooded Trotters.

REASONS FOR PERFORMING STUDY: Muscular changes caused by training are breed-specific and studies on the Norwegian-Swedish Coldblooded Trotter (NSCT) are limited. Knowledge about lactate-transporters in muscle in this light draught breed used for harness racing is lacking. OBJECTIVES: To identify muscular changes associated with training in young NSCTs and investigate muscular distribution of the monocarboxylate transporter 1 (MCT1) and its ancillary protein CD147, which facilitate lactate transport across membranes. METHODS: Nine horses were followed from the start of their training period until the end of their 3-year-old season. A biopsy sample of the middle gluteal muscle was collected on 4 occasions. On the last 3 sampling occasions, individual V(La4)-values (the speed corresponding to a blood lactate concentration of 4 mmol/l) were determined in an incremental exercise test on a high-speed treadmill. One horse was excluded due to lameness. Histochemical and immunohistochemical analyses were performed on all muscle samples to determine fibre types (I, IIA, IIAX, IIX), oxidative capacity (NADH) and the expression of MCT1 and CD147. The activity of selected metabolic enzymes in the muscle before and after training was determined. RESULTS: The percentage of type IIX fibres decreased with training while the percentage of type IIAX fibres increased. The activity of citrate synthase and 3-OH-acyl-CoA-dehydrogenase increased with training. The expression of MCT1 was lower in membranes and cytoplasm of type IIX fibres compared to all other fibre types both before and after training. The antibody against CD147 stained membranes and cytoplasm of all fibres. The first V(La4)-value was lower than the last 2 in all horses. CONCLUSIONS: Muscular changes with training of NSCTs were similar to those reported in Standardbreds, indicating fibre type transitions and increased oxidative capacity. Expression of MCT1 differed among fibre types and was related to the oxidative capacity of the fibres.