The influence of dietary fiber digestibility on the nitrogen requirements of mature horses

Mature geldings at maintenance were fed different diets in a 4 x 4 Latin square design balanced to account for residual effects in an attempt to determine whether differences in the digestibility of the fibrous portions of feedstuffs would influence dietary nitrogen (N) requirements. Diet 1 contained corn and soybean meal (SBM); diet 2, corn, corn oil and urea; diet 3, corn, SBM, straw and urea; diet 4, corn, alfalfa and urea. Urea supplied 50% of the total N in diets 2 and 3 and 39% of the total N in diet 4. The diets were fed in amounts that met National Research Council (NRC) recommendations for daily digestible energy intakes by mature horses at maintenance and met or exceeded total daily N requirements. True absorbed N was calculated by subtracting the fecal N associated with neutral detergent fiber (NDF-N) from total N intakes; true digestibilities of N ranged from 92.4 to 95.9%. Endogenous and metabolic fecal N excretions ranged from .37 to .56 g N/100 g dry matter intake. Although none of the diets as fed were deficient in N, apparent N digestibility was only 64% of N intake when the horses were fed the diet containing straw (diet 3), compared with 72.5 to 79.6% of total N intake among diets 1, 2 and 4 (P less than .01). Fecal excretions of water soluble, bacterial cell-associated and intestinal cell-associated N fractions were greatest when diet 3 was fed.(ABSTRACT TRUNCATED AT 250 WORDS)     

Gastric ulceration in mature thoroughbred horses

Routine post mortem examination of 195 Thoroughbreds in Hong Kong revealed that 66 per cent suffered from gastric ulceration. Racehorses killed straight out of training suffered a significantly greater incidence of ulceration (80 per cent) than those having been retired for a month or more (52 per cent). The macroscopic findings post mortem enabled a classification of equine gastric ulceration to be suggested (Types 1, 2, 3), according to severity. Severe lesions (Types 2 and 3) were present in 45 per cent of horses put down from training and 5 per cent of retired horses. This difference was significant. Lesions appeared to be chronically progressive during training, but to regress during retirement. The observed difference of gastric ulceration between the two groups of horses was similar for different age groups.     

Management of bladder rupture in mature horses

Rupture of the urinary bladder of adult horses is rare with both reports of surgical repair and conservative management in the literature. The case report by Gosling et al. in this issue describes the successful treatment of an iatrogenic bladder tear in an adult gelding. The aim of this commentary is to review the described treatment options.     

Headroom requirements for horses in transit

Horses intended for slaughter in Western Canada are frequently transported in double-deck trailers, where headroom may be restricted. Poll and withers height was estimated from type photographs of various horse breeds. The headroom required by Canadian legislation and codes of practice may not be sufficiently restrictive to protect the welfare of sport type horses when transported.     

Experimental Babesia equi infection in mature horses

Nine 4-year-old Arabian geldings were experimentally infected with Babesia equi of European origin. All horses developed detectable parasitemia an average of 30 days after they were inoculated, which was accompanied by a decrease in PCV. The infections were generally mild with no animal deaths. All horses became serologically positive by the indirect fluorescent antibody test within an average of 23 days after they were inoculated and by the complement-fixation test 30 days after they were inoculated.     

Dietary requirements and athletic performance of horses

There is no clear evidence that the chronic requirement for any non-energy yielding nutrient rises in proportion as the energy requirement increases with hard work. The need for protein, and probably that for calcium, remain a function of bodyweight daily. Some proportionality with energy may exist for certain nutrients, although the evidence has not been adduced. For example, because of an increase in both the proportion and amount of propionic acid in the volatile fatty acids of caecal contents, the tissue requirement for vitamin B12 may rise with an increase in the rate of energy metabolism. Exercise influences appetite and therefore voluntary intake, and consequently the daily intake of nutrients. Although that intake is not just a function of dietary bulk and weight, it is necessary to increase energy concentration of diets to achieve an adequate chronic intake of energy where work intensity and energy expenditure are considerable. Acute nutrient requirements paint a different picture from chronic requirements. An increase in total feed intake, or the density of that feed, would neither satisfy these requirements nor be a desirable means of doing so. The acute needs of water, electrolytes and soluble carbohydrates should be met by dosing when the need arises. The timing of the consumption of energy yielding substrates relative to that of exercise may be critical to performance. An inevitable postprandial consequence of a meal of starch or protein by the resting horse, is an increase in the activity of plasma insulin. This increase decreases blood glucose, depriving muscles of a critical substrate, but the assertion has not been resolved by experiment in horses. Experiments are required to ascertain the optimum feeding regime during the 24 h preceding extreme exertion. Whereas exhaustion in sprint work is largely a function of elevated blood lactate concentration, that of extended work is a consequence of a decline in glycogen reserves and losses of body fluid and electrolytes. Glycogen loading is of benefit to many long distance human athletes, but no advantage has yet been established for this practice in horses, and without modification it could render them subject to laminitis and endotoxaemia. Nevertheless supplementation of horses with water, glucose and electrolytes during work may benefit their endurance. The provision of 5 litres water every 2 h with 30 g salt, or twice as much of mixed electrolytes, and 15 g sucrose or glucose, is recommended for a 500 kg horse during periods of extreme sweating.(ABSTRACT TRUNCATED AT 400 WORDS)     

Branchial remnant cysts of mature and juvenile horses

This clinical report describes 8 cases of branchial remnant cysts (BRC) in the horse. The horses presented with bimodal age distribution, with 5 cases in mature horses (age 8–21 years) and 3 in foals (age 1, 6 and 10 months). Mature cases presented for dysphagia or intermittent oesophageal obstruction (2/5), and retropharyngeal swelling (3/5), whereas respiratory stridor and visible mass were presenting complaints in the foals. Presence of a right‐sided (5/8) or dorsally located (2/8) palpable retropharyngeal mass of 3–35 cm diameter was noted clinically; one left‐sided mass was identified as an incidental finding at necropsy. Ultrasonography typically revealed a thick‐walled cyst containing hypoechoic fluid with dependent hyperechoic masses consistent with blood clots. Radiographs and upper airway endoscopy were also consistent with a retropharyngeal mass. Fluid cytology revealed chronic haemorrhage in 6/8 cases, and squamous epithelial cells in one case. Histopathology in all cases demonstrated an epithelium‐lined cyst with no smooth muscle or thyroid tissue. Two cases was subjected to euthanasia; one due to concurrent laryngeal anomalies and one due to financial constraints. The remaining 5 cases were treated via surgical excision. Post operatively, right laryngeal hemiplegia was observed in 4/5 cases. All previous reports of BRC in the horse have described juvenile individuals. Brachial remnant cyst should be considered a differential diagnosis for mature horses with masses of the throatlatch area and can be definitively diagnosed by the presence of squamous epithelium in aspirated fluid or by histopathology of the excised mass. Right recurrent laryngeal nerve damage is a common complication of surgery.     

Respiratory responses of mature horses to intravenous lobeline bolus

The respiratory stimulant lobeline has been used in equine clinical practice to increase inspiratory and expiratory airflow rates at rest in order to facilitate investigation of both lower and upper airway function. Some of the responses to lobeline in the pony have been reported, but the detailed time course, effect of dose, possible side effects and reproducibility associated with lobeline administration have not been described in the horse. Respiratory airflow rates and oesophageal pressure were measured with a Fleisch No. 5 pneumotachometer and lightweight facemask and a microtip pressure transducer catheter, respectively. The output of the Fleisch pneumotachometer was calibrated for flow rates up to +/- 70 l/s. Seven mature horses with no clinical signs of respiratory disease were studied. Investigations were conducted to determine: (1) the responses to different doses of lobeline (0.15, 0.20, 0.25 and 0.30 mg/kg bwt) as a rapid i.v. bolus (6 horses); (2) arterial blood gases during and after lobeline administration (0.20 mg/kg bwt; 3 horses); and (3) the reproducibility of lobeline-stimulated hyperpnoea (5 horses; 2 doses of 0.20 mg/kg bwt lobeline, 15 min apart). All horses tolerated the lobeline-stimulated hyperpnoea well, although one always coughed or snorted at the onset. Mild tremor was noted following the highest dose in several horses. Apnoea of approximately 40 s was common after the hyperpnoea. Both tidal volume (VT) and frequency (fR) increased with lobeline dose. During peak hyperpnoea at a dose of 0.30 mg/kg bwt, peak inspired flow rate (PIF), peak expired flow rate (PEF) and minute ventilation (VE) were mean +/- s.e. 41+/-5 l/s, 61+/-10 l/s and 920+/-99 l/min, respectively. The hyperpnoea also caused marked changes in arterial PaO2, PaCO2 and pHa at 90 s after lobeline (0.20 mg/kg bwt) administration (mean +/- s.e. 146.0+/-6.9 mmHg, 20.6+/-0.8 mmHg and 7.707+/-0.020, respectively) compared to at rest (mean +/- s.e. 104.0+/-4.0 mmHg, 50.6+/-2.8 mmHg and 7.432+/-0.012). Dynamic lung compliance (Cdyn) was unaltered by lobeline administration. The lobeline-induced hyperpnoea was highly reproducible, with no significant difference in any of the parameters during 2 stimulations 15 min apart. Lobeline induced highly reproducible responses without any apparent adverse effects and may be useful in the investigation of pulmonary function in healthy horses and those with airway disease.     

Thyroid function in mature horses ingesting endophyte-infected fescue seed

OBJECTIVE: To determine whether ingestion of fescue seed infected with the endophyte Neotyphodium coenophialum would alter thyroid function in adult horses. DESIGN: Original study. ANIMALS: 4 adult mares that were not pregnant and 6 adult geldings. PROCEDURE: Thyrotropin releasing hormone stimulation tests were performed while horses received a standard diet and after infected seed (2.3 kg/d [5 lb/d]) had been fed for 1 and 2 months. Serum prolactin concentrations were measured to verify endophyte absorption. RESULTS: Serum prolactin concentrations indicated that at least 8 of 10 horses absorbed the endophyte. Baseline concentrations of thyroid stimulating hormone, total and free triiodothyronine, and total and free thyroxine and the change in hormone concentrations in response to administration of thyrotropin releasing hormone (1 mg, i.v.) were not altered by ingestion of endophyte-infected fescue seed. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that ingestion of fescue seed infected with the endophytic fungus N. coenophialum for 2 months has little effect on thyroid function in adult horses that are not pregnant.     

Nitrogen metabolism in mature horses at varying levels of work

Nitrogen metabolism was measured in five mature geldings performing varying levels of work that simulated race training. Following an initial maintenance period without forced exercise, workload was increased in succeeding 18-d periods by doubling the distance the horses were galloped in each period from period 2 through 4. A 4-d N balance experiment was conducted at the end of each 18-d period. The maximum distance galloped daily, which was in period 4, was repeated in period 5. Then, workloads were decreased through period 7. Nitrogen balance was determined in two additional periods, 8 and 9, while the geldings were at maintenance with no forced exercise. Geldings were fed diets containing similar protein-to-calorie ratios in all periods. Nitrogen retention increased (P less than .05) as workload increased from period 1 to period 3 and remained elevated throughout the rest of the experiment. Nitrogen retention did not (P greater than .05) decrease from highest values, observed at maximum workload during periods 4 and 5, until period 9, which was 34 d postexercise during a maintenance period. Nitrogen retention was higher (P less than .05) following training than before training.