Gross, histological and histomorphometric features of the navicular bone and related structures in the horse

Forelimb navicular bones and associated soft tissues were collected from 3 groups of horses and subjected to pathological examinations. The groups consisted of 38 horses with clinical navicular disease (ND) and 2 control groups, with no history of forelimb lameness, consisting of 25 age-matched mature horses (A-MC) and 9 immature horses (IC). Histological and histomorphometric studies were performed on tissue samples from 10 ND, 10 A-MC and 5 IC horses. Gross changes seen only in ND horses included: full thickness defects in the palmar surface fibrocartilage, palmar cortex erosion, medullary lysis, flexor digitorum profundus tendon (FDPT) surface fibrillation, FDPT core lesions and adhesions between the FDPT and navicular bone. Palmar surface partial thickness fibrocartilage loss and distal border fragmentation were seen with a significantly greater incidence in ND than in A-MC and not observed in IC. Remodelling of the proximal border, FDPT surface colouration, palmar surface fibrocartilage colouration and proximal border entheseous bone were identified in ND and A-MC but not in IC. Mid-ridge synovial fossae and horizontal depressions in the palmar surface were identified in all groups. Histologically palmar fibrocartilage thinning and loss were associated with reduced palmar fibrocartilage cell density and chondrocyte cluster formation. Palmar fibrocartilage fibrillation, palmar cortical bone defects, fibromyxoid stromal change in the medulla, medullary pseudocyst formation and entheseous new bone formation were all seen in ND. The adjacent FDPT showed fibrillation, tag formation and degeneration of the dorsal surface. Necrotic foci were also present within the body of the tendon. Although not always present, medullary bone pseudocysts, separate mineralised foci and most changes on the dorsal surface of the FDPT were specific to ND. Bone histomorphometric parameters were compared among groups. Cross-sectional area reduced from the sagittal ridge to the medial and lateral margins of each navicular bone. IC navicular bones had a smaller subchondral area, subchondral bone volume and a greater osteoid volume than in the AC, indicating that these differences were age-related. In ND the medullary area was decreased but the trabecular bone volume increased. The palmar subchondral area was increased but contained bone with an increased porosity and osteoid volume. Changes occurred from the medial to the lateral margins of the bone in horses with ND indicating remodelling of the bony elements throughout the bone in ND. The histological and histomorphometric changes in the navicular bone and palmar fibrocartilage were considered similar of those found in articular hyaline cartilage and subchondral bone in osteoarthritis.

Tapeworm infection is a significant risk factor for spasmodic colic and ileal impaction colic in the horse

The association between the equine intestinal tapeworm Anoplocephala perfoliata and specific types of intestinal disease was investigated by matched case-control study using coprological and serological diagnosis. We have previously shown that the host IgG(T) response to 12/13 kDa antigens of A. perfoliata correlates well with infection intensity, therefore this antibody response was used to investigate the risk of colic at different levels of parasite infection intensity. One hundred and three spasmodic colic cases with an equal number of controls matched for age, breed and gender, and 20 ileal impaction cases each with 2 similarly matched controls were obtained. Cases of spasmodic colic were much more likely (odds ratio = 8.0) to be associated with A. perfoliata infection detected coprologically than controls. Serological diagnosis revealed an increasing risk of spasmodic colic with increasing infection intensity. Calculation of an aetiological fraction suggests that 22% of spasmodic colic cases in this study were tapeworm associated. No significant association was found between colic and strongyle egg count. Conditional logistic regression analysis demonstrated that the relationship between colic and A. perfoliata infection intensity was not confounded by strongyle egg count and there was a linear relationship between infection intensity and the log-odds of spasmodic colic. For cases of ileal impaction, a strong association was found between colic and A. perfoliata as diagnosed by coprological means (odds ratio of 34.0). Serological diagnosis also revealed a strong association that increased with higher levels of infection intensity (odds ratio = 26.0). The aetiological fraction for the ileal impaction data suggests that 81% of the ileal impaction cases in this study were tapeworm associated. This study concludes that A. perfoliata is a significant risk factor for spasmodic colic and ileal impaction colic in the horse; and that the risk of spasmodic colic increases with infection intensity.

Thermoregulation. Base mechanisms and hyperthermia

Metabolic HP is extremely high during exercise in horses. Thermoregulation in horses is primarily dependent on evaporative heat loss from sweating in particular. Under thermoneutral conditions, these mechanisms are sufficient to allow horses to perform high-intensity exercise for long periods. Under thermally stressful conditions, particularly in high ambient humidity, the efficiency of evaporative heat loss mechanisms is compromised and may result in horses developing hyperthermia. Early recognition and vigorous treatment are essential to limit the consequences of heat stress in horses. Meticulous planning and management of equestrian events that are held under thermally stressful conditions are essential to ensure the welfare of competing horses and their riders. The conditioning program of horses expected to compete under thermally stressful conditions must also make adequate provision for acclimatization to the hot, humid conditions.

Variations in systemic and pulmonary endothelin-1 in horses with recurrent airway obstruction (heaves)

Recurrent airway obstruction (RAO) is an asthma-like condition of the horse that represents a major cause of morbidity and loss of performance. The exact pathogenesis of asthma in man is unclear but the role of endothelin (ET) is currently under investigation, thus sparking interest in the bronchoconstrictive and vasoconstrictive properties of endothelin in the equine-specific disease entity. In this study, we investigated the levels of ET-1 in systemic blood, as well as in bronchoalveolar lavage (BAL) from horses with RAO. We also studied how these values might correlate with those of lung function tests and pulmonary artery pressure. Five horses with RAO were evaluated both in remission and in crisis and compared to five control horses. RAO horses had significantly (P<0.05) higher systemic ET-1 levels than control horses. They also had a negative arteriovenous ET-1 difference that may correspond to a net uptake of ET-1 in the lung. RAO horses in crisis had increased amounts of immunoreactive ET in BAL fluid compared to normal control subjects. Additionally, the reduction in lung function seen in RAO horses in crisis was significantly correlated with lower epithelial lining fluid ET-1 levels. Our results demonstrate that endothelin may contribute to the pathogenesis of asthma.

Treatments affecting fluid and electrolyte status during exercise

A number of feeding and management practices, dietary electrolyte supplements, and medications may affect fluid and electrolyte status in resting and exercising horses. The contents of the gastrointestinal tract of the equine athlete, unlike its human counterpart, are responsible for more than 10% of body weight. Although ingesta traditionally has been considered dead weight for the sprinting horse, it is a valuable reservoir of fluid and electrolytes that may be used during endurance exercise. Numerous strategies for hyperhydration of the equine athlete and for replacement of fluid and electrolytes lost via sweating were developed in preparation for competing in the hot and humid climate of the 1996 Olympic Games in Atlanta. These strategies have implications for all equine athletes. Medications, including sodium bicarbonate, furosemide, and acetazolamide commonly are used to enhance performance by either buffering alterations in fluid and electrolyte homeostasis or by ameliorating the effects of other conditions that may limit performance.

Sperm transport and survival in the mare

Following the deposition of semen in the mares uterus, spermatozoa must be transported to the site of fertilization, be maintained in the female tract until ovulation occurs, and be prepared to fertilize the released ovum. Sperm motility, myometrial contractions, and a spontaneous post-mating uterine inflammation are important factors for the transport and survival of spermatozoa in the mares reproductive tract. Fertilizable sperm are present in the oviduct within 4 hours after insemination. At this time, the uterus is the site of a hostile inflammatory environment. Our data suggest that spermatozoa trigger an influx of polymorphonuclear neutrophils (PMNs) into the uterine lumen via activation of complement. Furthermore, seminal plasma appears to have a modulatory effect on the post-mating inflammation through its suppressive effect on PMN chemotaxis and migration. Spermatozoa that safely have reached the oviduct can be stored in a functional state for several days, but prolonged sperm storage in the female tract is not required for capacitation and fertilization in the horse. The caudal isthmus has been proposed as a sperm reservoir in the mare. The pattern of sperm transport and survival of spermatozoa in the mares reproductive tract are different between fertile and subfertile stallions, between fertile and some infertile mares, and between fresh and frozen-thawed semen. Possible explanations for these differences include a selective phagocytosis of damaged or dead spermatozoa, impaired myometrial activity in subfertile mares, bio-physiological changes of spermatozoa during cryopreservation, and the removal of seminal plasma during cryopreservation of equine semen.

Atrial fibrillation associated with central nervous symptoms and colic in a horse: a case of equine cardiomyopathy

A 18-year-old Dutch Warmblood mare was referred for colic. Upon arrival, lethargy, blindness, head pressing, ataxia, and circling were the main clinical signs. On rectal examination a hard mass and oedema around the cranial mesenteric artery were palpated. Plasma liver enzyme activities and the ammonia level were elevated. Atrial fibrillation with a pulse frequency of 36-52 beats per minute was noticed. On both sides a holosystolic murmer with the maximum intensity on the right side could be auscultated. Postmortem examination revealed eccentric hypertrophy of the right atrium and a pale spotted myocardium, most prominently of the right ventricle, with secondary venous congestion of the azygos and mesenteric veins. The liver changes were indicative of chronic congestion. Despite the normal pulse rate, it appeared that congestive heart failure due to cardiomyopathy, was responsible for the presenting symptoms of this patient.

Stress responses of horses during a long period of transport in a commercial truck

OBJECTIVES

To characterize progressive patterns of dehydration, stress responses, and water consumption in horses transported long distances in hot weather and to evaluate various measurements in detecting dehydration and stress in transported horses.

DESIGN

Prospective study.

ANIMALS

30 mature, healthy horses.

PROCEDURE

The following 4 treatment groups were studied: horses that were penned and offered water every 5 hours (n = 5), horses that were penned and not offered water (5), horses that were transported in a truck and offered water every 5 hours (10), and horses that were transported and not offered water (10). The study commenced after 6 hours of water deprivation. Every 4 hours, the truck returned to the pen area and body weights were measured, physical examinations were performed, and blood samples were obtained. During this 1-hour period, water was offered to some horses, depending on treatment group.

RESULTS

After 24 hours of transport, 3 horses were judged unable to continue and the study was terminated. Horses that were penned and offered water drank a mean of 38.2 L and horses that were transported and offered water drank 20.9 L, but some of the latter horses did not drink until after 19 or 24 hours of transport. In horses that were transported or penned and not offered water, serum electrolyte concentrations were greater than reference range values by 19 hours. Most horses that were transported and offered water consumed adequate water to postpone severe dehydration beyond 24 hours.

CLINICAL IMPLICATIONS

Tame horses in good condition and initially deprived of access of water for approximately 6 hours can be transported in groups in open trailers during hot, humid conditions for up to 24 hours before dehydration and fatigue become severe. Rectal temperature and appearance of the horses were the most useful measures for determining crisis situations.

Effects of inhaled beclomethasone dipropionate on respiratory function in horses with chronic obstructive pulmonary disease (COPD)

The effects of beclomethasone dipropionate on pulmonary function and arterial blood gas values were investigated in horses with chronic obstructive pulmonary disease (COPD). Six mature mares, diagnosed as having COPD based on clinical signs, cytological examination of bronchoalveolar lavage and pulmonary function testing, were used. Beclomethasone dipropionate (3750 microg) was administered b.i.d. for a 2 week period with a metered dose inhaler using a mask. Pulmonary function tests and arterial blood gas analyses were performed at weekly intervals, starting before beclomethasone administration and for 4 weeks thereafter. Upper airway endoscopy and nasopharyngeal fungal cultures were performed before and after treatment. Maximal variations in transpulmonary pressure (deltaPL) were elevated in all horses at baseline. Beclomethasone administration resulted in a significant decrease in deltaPL in 5 horses, and deltaPL fell to within the normal range in 4 horses. Two weeks after the end of treatment, deltaPL was at or above baseline values in all horses. Total pulmonary resistance and elastance decreased significantly during treatment and returned to or above baseline values after the administration of beclomethasone was discontinued. At baseline, PaO2 range was 53-90 mmHg. In 4 horses with pronounced laboured breathing, PaO2 increased with treatment. One horse became reluctant to inhale the beclomethasone after one week, and only a transient improvement in respiratory function was noted in this animal. One horse developed a mild lower airway infection 24 h after the beginning of treatment, but no other possible side effects were noticed. Pharyngeal fungal cultures were negative before and after treatment. It can be concluded from the results of this study that inhaled beclomethasone dipropionate causes a marked improvement of respiratory function in horses with COPD.

Scintigraphic and clinical findings in the Standardbred metatarsophalangeal joint: 114 cases (1993-1995)

To correlate scintigraphic and clinical findings of the metatarsophalangeal joint (MTPJ) in Standardbreds, radiographic findings in horses with confirmed MTPJ lameness, and determine if stress reaction and more advanced bone remodelling occurred in the MTPJ, medical records of 114 Standardbreds admitted between September 1993 and April 1995 in which bone scintigraphy included standing lateral and plantar views of the metatarsophalangeal joint (MTPJ) were reviewed. Images obtained using a large field of view gamma camera were evaluated visually for location, definition and intensity of increased radioisotope uptake (IRU), which was graded as mild, moderate, or intense. Clinical history and lameness examination findings were recorded and, in horses with documented MTPJ lameness, radiographic examination included the 30 degree (down-angled) dorsolateral 45 degree plantaromedial view thought to be useful in evaluation of the plantarolateral condyle of the third metatarsal bone (MtIII). The most common abnormality, IRU of the plantarolateral aspect of MtIII, was seen in 67 horses, and horses were further classified according to scintigraphic and clinical findings. In 43 horses in which lameness was not localised to the MTPJ, mild (32 horses), moderate (10 horses), and intense (one horse) IRU of MtHII was found. In 24 horses with lameness localised to the MTPJ, moderate (18 horses) and intense (6 horses) IRU was found. Of 18 horses with moderate IRU of MtIII, 9 had radiographic evidence of abnormal bony remodelling of MtIII, whereas 5 of 6 horses with intense IRU had radiographic changes. In 12 horses with MTPJ lameness and radiographic evidence of bony remodelling without fracture, radiographic changes consisted of plantarolateral subchondral radiolucency and sclerosis (7 horses), radiolucency and osteochondrosis (one horse), and plantar MtIII sclerosis without radiolucency (4 horses). In 2 horses with moderate IRU and MTPJ lameness, radiographic evidence of radiolucency and MtIII fracture was found. Of 19 starters with MTPJ lameness and IRU of MtIII, 18 horses raced after diagnosis, but only 13 remained at the same racing class or improved. The results of this study suggest the most common scintigraphic abnormality of the MTPJ, IRU of the plantarolateral aspect of MtIII, may precede other stress-related changes, and in some horses is associated with a continuum of stress-related subchondral bone remodelling which results in lameness and later radiographic changes. Since 24 of 35 horses with moderate or intense IRU of MtIII had MTPJ lameness, and 5 of 7 horses with intense IRU of MtIII had lameness and radiographic evidence of abnormal remodelling, it was concluded that horses with advanced, scintigraphic findings are more likely to have lameness and radiographic evidence of subchondral bone damage.

Environmental control to maintain stabled COPD horses in clinical remission: effects on pulmonary function

The objective of this study was to test the hypothesis that stabled COPD horses can be maintained in clinical remission by replacing hay by grass silage and bedding made of wood shavings (Period B) and of wheat straw (Period C) during 6 weeks, respectively. At the end of these different periods, the pulmonary function of the horses was assessed by mechanics of breathing and arterial blood analyses. These results were compared to those measured in clinical remission obtained after 2 months in pasture (Period A). No significant difference was observed between these 3 periods neither to values obtained for healthy horses placed during 6 weeks in a hay environment. For all that, COPD horses placed in contact with hay in the same barn developed within mean +/- s.d. 8+/-3 days clinical signs of heaves and significant alterations of pulmonary function parameters.

Does an acute COPD crisis modify the cardiorespiratory and ventilatory adjustments to exercise in horses?

The present study was conducted to understand better the mechanisms leading to the decrease in exercise capacity observed in horses suffering from chronic obstructive pulmonary disease (COPD). Five COPD horses were submitted to a standardized submaximal treadmill exercise test while they were in clinical remission or in acute crisis. Respiratory airflow, O2 and CO2 fractions in the respired gas, pleural pressure changes and heart rate were recorded, and arterial and mixed venous blood were analyzed for gas tensions, hemoglobin, and plasma lactate concentrations. O2 consumption, CO2 production, expired minute ventilation, tidal volume, alveolar ventilation, cardiac output, total pulmonary resistance, and mechanical work of breathing were calculated. The results showed that, when submaximally exercised, COPD horses in crisis were significantly more hypoxemic and hypercapnic and that their total pulmonary resistance and mechanical work of breathing were significantly higher and their expired minute ventilation significantly lower than when they were in remission. However, their O2 consumption remained unchanged, which was probably due to the occurrence of compensatory mechanisms, i.e., higher heart rate, cardiac output, and hemoglobin concentration. Last, their net anaerobic metabolism seemed to be more important.

Long-term prospects for horses with grass sickness (dysautonomia)

Responses to questionnaires were received from 31 owners of horses or ponies treated for chronic grass sickness (dysautonomia). Contrary to previous opinions the respondents indicated that the majority of the animals were capable of strenuous work, had regained the weight they had lost and, apart from a few residual problems such as difficulty in coping with dry fibrous food, had returned to a normal life. They had recovered slowly and had involved the owners in considerable extra work, but all the owners indicated that they considered the effort to have been worthwhile.

[The spontaneous reduction of a twin pregnancy in two mares]

Twin pregnancies are a serious problem in stud medicine as they terminate in most cases in abortion, stillbirth or the delivery of dead or weak and deformed foals. In recent years, the introduction of sonography has greatly improved the management of mares with twin conceptuses, in particular monitoring the phenomenon of spontaneous embryo reduction to a single vesicle. This allows supervision of pregnancy with relatively little expenditure and loss of time. We document the spontaneous reduction to single vesicles of unilateral twin pregnancies in a draught- and a warmblood-mare. In both mares diagnosis of twins was made 17 days after covering; they probably resulted from synchronous double-ovulations. After another 5 days, distinct signs of the loss of one conceptus were recognized and, subsequently, only single pregnancies existed. No interventions were necessary.

Ultrasound spirometry in the horse: a preliminary report on the method and the effects of xylazine and lobeline hydrochloride medication

A new computerised ultrasound-based spirometry system according to Buess et al. (1995) modified by a double flow measurement facility was used to study pulmonary function in healthy horses and horses affected with subclinical and manifest chronic bronchiolitis (CB). The horses were first evaluated at rest without any medication. On another occasion all horses were tested following i.v. administration of xylazine (0.4 mg/kg) and following i.v. administration of lobeline hydrochloride (l.hy.; 0.2 mg/kg) to evaluate the effect of xylazine and l.hy. on different spirometric variables. Ultrasound-based spirometry proved to be an easily applicable method for lung function testing, even in difficult horses. However, there existed a pronounced physiological variation for all measured lung function parameters and no significant differences between healthy horses and horses with chronic bronchiolitis could be found except for the expiratory tidal volume (VTE p < 0.05). Individually, a marked decrease of variability from breath to breath following either xylazine and l.hy. administration could be observed for all parameters, except the flow-time-ratio (Tpef./ Texp.) and the flow-volume-ratio (Vpef./Vexp).

Subchondral bone failure in an equine model of overload arthrosis

Gross examination of metacarpo-/metatarsophalangeal (fetlock) joints from racehorses revealed defects on the condylar surface that ranged from cartilage fibrillation and erosion to focal cartilage indentations and cavitation in subchondral bone characteristic of traumatic osteochondrosis. Because these lesions represented a spectrum of mechanically induced arthrosis in which microdamage is thought to play a role, a histologic study of sagittal sections was made to study the morphogenesis. Subchondral bone failure developed beneath a flattened section of the condyle where the margin of the sesamoid bone produces compression as well as shear on impact of the foot with the ground. Milder lesions had thickening of subchondral bone and underlying trabeculae. With advancing sclerosis an increased amount of osteocyte necrosis was present. Occasional vascular channels with plugs of matrix debris and cells were present just beneath the cartilage. There was increased prominence of subchondral vessels, and osteoclastic remodeling was seen in and around the sclerotic zone. Apparent fragmentation lines in the subchondral bone suggested increased matrix fragility. Irregular trabecular microfractures developed at a depth of a few millimeters. Increased vascularity with hemorrhage, fibrin, and fibroplasia could be seen in enlarged marrow spaces at this more advanced stage. The overlying articular cartilage was variably indented but remained largely viable with degeneration and erosion limited to the superficial layers. Focally, breaks in the calcified layer appeared to lead to collapse and cartilage infolding. In metacarpal condyles from experimental horses run on a treadmill, there were milder changes at the site. The subchondral bone was increased in volume and there was increased diffuse staining with basic fuchsin, but no increase in the number of microcracks was seen. The findings in the racehorses indicate that the equine fetlock condyle is a consistent site of overload arthrosis in which microfracture and failure in subchondral bone may occur. Controlled exercise in treadmill horses may provide a model in which to study the pathogenesis.

Videoendoscopic assessment of dynamic laryngeal function during exercise in horses with grade-III left laryngeal hemiparesis at rest: 26 cases (1992-1995)

OBJECTIVE

To evaluate laryngeal function by means of videoendoscopy during high-speed treadmill exercise in racehorses with grade-III left laryngeal hemiparesis at rest and to determine outcome of treatment.

DESIGN

Retrospective study.

ANIMALS

26 racehorses.

PROCEDURE

Videoendoscopy of the larynx was performed while horses were at rest and exercising on a treadmill. Horses were classified as having grade-IIIA, -IIIB, or -IIIC laryngeal hemiparesis on the basis of the degree of arytenoid cartilage abduction maintained during exercise. Postoperative racing performance was determined by evaluating race records and conducting telephone surveys.

RESULTS

20 (77%) horses had grade-IIIC laryngeal hemiparesis (i.e., severe dynamic laryngeal collapse during exercise). Eighteen underwent surgery, and racing performance was improved in 9. Five (19%) horses had grade-IIIB laryngeal hemiparesis (i.e., left arytenoid cartilage and vocal fold were maintained in an incompletely abducted position during exercise). Four underwent surgery, and racing performance was improved in 1. One (4%) horse had grade-IIIA laryngeal hemiparesis (i.e., full abduction of arytenoid cartilage during exercise); surgery was not performed.

CLINICAL IMPLICATIONS

Videoendoscopy is useful in determining dynamic laryngeal function in racehorses with grade-III laryngeal hemiparesis at rest.

Pericarditis in horses: 18 cases (1986-1995)

OBJECTIVE

To determine clinical signs of pericarditis in horses and to determine whether there were any relationships among clinical signs, echocardiographic findings, treatment, and outcome.

DESIGN

Retrospective study.

ANIMALS

18 horses.

RESULTS

Physical examination was performed on 16 horses. Cardiovascular abnormalities included tachycardia (n = 16), pericardial friction rub (10), venous distention (7), murmur (7), muffled heart sounds (6), weak arterial pulse (6), jugular pulse (6), and edema (5). Twelve horses also had respiratory abnormalities; the most common was dull lung sounds, ventrally, suggestive of pleural effusion (10). Echocardiography was the most important tool for diagnosis of pericarditis. Detection of clinical signs of right-sided heart failure was significantly associated with severe accumulation of pericardial effusion and with detection of cardiac compromise. Severe accumulation of pericardial effusion was also significantly associated with echocardiographic detection of cardiac compromise. Pericarditis was idiopathic in 6 horses, and bacterial in 5. Five horses had nonseptic pericarditis associated with bacterial respiratory disease, and 2 had nonseptic pericarditis associated with viral respiratory disease. Fourteen of the 18 horses were treated specifically for pericarditis; 10 received antimicrobials and 6 with suspected immune-mediated pericarditis received corticosteroids. Pericardial drainage and lavage were performed on 6 horses in which pericardial effusion or fibrin accumulation was compromising cardiac function. Pericarditis resolved in all 14 horses that were treated, and all 14 returned to their prior intended use.

CLINICAL IMPLICATIONS

With early detection of disease and aggressive treatment, the prognosis for horses with pericarditis is good.

The effects of partial thyroidectomy on the development of the equine fetus

A syndrome of congenital hypothyroidism and dysmaturity has been an important cause of reproductive loss and foal mortality in western Canada. The cause and pathogenesis of this syndrome is under investigation. One issue to be addressed is whether all the anomalies present in affected foals are produced concurrently by the same agent, or if affected foals are primarily hypothyroid in utero which induces the associated lesions. This study was designed to document the effects of fetal thyroidectomy, at about 215 days of gestation, on the growth and development of the equine fetus and to compare the anomalies present to those reported in the spontaneously occurring syndrome of foals in western Canada. Two sham-operated controls and 4 partially thyroidectomised foals were carried to term following surgery. Sham-operated control foals were normally developed. Partially thyroidectomised foals were hypothyroid; had hyperplastic thyroid gland remnants; abnormal behaviour and locomotor skills; and numerous, marked deficiencies in their skeletal development. The anomalies present in partially thyroidectomised foals were comparable to those reported in congenitally hypothyroid neonates of other species, including human infants, and were similar to those described in congenitally hypothyroid and dysmature foals reported in western Canada.

Relationship between hind limb lameness and radiographic signs of bone spavin in Icelandic horses in Sweden

A field study was designed to estimate the prevalence of hind limb lameness in a population of Icelandic horses in Sweden. All available Icelandic horses at 11 different farms within 150 km from Uppsala were examined once during a study period of 13 months. The relationship between hind limb lameness and radiographic signs of bone spavin (RSBS) was investigated. The rate of agreement between the outcome after palpation, motion evaluation and flexion test and radiographic examination was established. A total of 379 horses including 238 geldings, 125 mares and 16 stallions, with mean age 8.1 years (range 1-19 years) were examined by palpation of the medial aspect of the tarsal joints, motion evaluation and flexion test of the hind limbs. One dorsolateral-plantaromedial oblique radiographic view was recorded from each tarsus. Palpable abnormalities were found in 118 horses (31%). Forty-three horses (12%) were lame at presentation, 94 horses (25%) were positive on flexion test and 88 horses (23%) had RSBS. There was a significant relationship between palpable abnormalities, lameness, positive flexion test and RSBS. The proportion of joints with RSBS increased with increasing severity of physical findings. The proportion of lame limbs increased with increasing radiographic changes. The presence of palpable findings or positive flexion test was not influenced by the grading of radiographic changes. Using palpation, motion evaluation, and flexion test 75% of the horses with RSBS were identified. The rate of agreement between the clinical examination and the radiographic examination was 73%.

Effect of platelet-activating factor antagonist L-691,880 on low-flow ischemia-reperfusion injury of the large colon in horses

OBJECTIVE

To determine the effect of platelet-activating factor (PAF) antagonist L-691,880 on low-flow ischemia and reperfusion (I-R) of the large colon in horses.

ANIMALS

12 adult horses.

EXPERIMENTAL DESIGN

Horses were anesthetized, and the large colon was exteriorized through a ventral median celiotomy and instrumented. Colonic arterial blood flow was reduced to 20% of baseline (BL) and maintained for 3 hours; flow was then restored, and the colon was reperfused for 3 hours. One of two solutions was administered intravenously 30 minutes before reperfusion: group 1, 10 mL/kg 0.9% NaCl; and group 2, 5 mg/kg PAF antagonist L-691,880 in 0.9% NaCl. Hemodynamic variables were monitored and recorded at 30-minute intervals. Systemic arterial and colonic venous blood were collected for measurement of blood gas tensions, oximetry analyses, packed cell volume, and total plasma protein concentrations. Colonic venous blood was collected for determination of lactate, 6-keto prostaglandin F1 alpha (6-kPG), prostaglandin E2 (PGE2), and thromboxane B2 (TXB2) concentrations. Full-thickness biopsy specimens were harvested from the left ventral colon for histological evaluation.

RESULTS

There were no significant differences between the two groups for any hemodynamic or metabolic variables. Colonic venous pH decreased, and carbon dioxide tension and lactate concentration increased during ischemia but returned to BL values during reperfusion. Colonic venous 6-kPG concentration was significantly increased above BL value at 2 hours and remained increased through 6 hours in horses of both groups. Colonic venous PGE2 concentration was significantly greater in group 2 compared with group 1 throughout the study. Colonic venous PGE2 concentration was increased above BL value from 3 to 6 hours in horses of both groups. Colonic venous TXB2 concentration was not different between groups but was significantly increased above the BL value for the first hour of reperfusion. Low-flow I-R of the large colon caused significant mucosal necrosis, hemorrhage, edema, and neutrophil infiltration; however, there were no differences in histological variables between vehicle-control and PAF antagonist-treated horses.

CONCLUSION

No protective effects of PAF antagonist L-691,880 were observed on colonic mucosa associated with low-flow I-R. Additionally, deleterious drug-induced effects on hemodynamic and metabolic variables and colonic mucosal injury were not observed.

Post exercise changes in compartmental body temperature accompanying intermittent cold water cooling in the hyperthermic horse

Whereas the efficacy of cold water cooling of horses has been demonstrated by several studies, the dynamics of temperature changes within and between compartments (primarily muscle, blood [core], skin and deep core [rectal]) have not been investigated. Changes in body temperature associated with cold water cooling were investigated in the hyperthermic horse. Muscle (TMU), pulmonary artery (TPA), rectal (TREC), tail-skin (TTSK) and coat surface (TCOAT) temperatures, were monitored continuously in 5 Thoroughbred horses during and after exercise in hot humid (30 degrees C and 80% RH) conditions on a treadmill. Horses were cooled in the hot humid environment with cold water (approximately 6 degrees C) for 6 30 s periods. Between each 30 s cooling period the horses stood for 30 s. A total of 180 l of cold water was applied. Horses were monitored for a further 4 min following the final cooling period. From the end of exercise to the end of the final cooling (6.5 min), mean (+/- s.e.) rates of decrease for TTSK and TPA were similar (0.8 +/- 0.1 and 0.8 +/- 0.1 degrees C/min, respectively). The effects on TMU and TREC were less marked, with average rates of 0.2 +/- 0.1 and 0.0 +/- 0.1 degrees C/min, respectively. During the first 4 min of cooling, TPA fell during the 30 s period of water application and rose during each 30 s period of standing. When TPA fell below approximately 36.5 degrees C, these variations were suppressed and TPA rose steadily, despite continued applications; TREC and TMU continued to fall, although less rapidly than before. These observations are consistent with the onset of skin vasoconstriction at low TPA. The mechanism is mediated through a cooling of circulating blood volume providing a greater capacity for heat transfer between muscle and circulation. Intermittent application of cold water (approximately 6 degrees C) improves heat removal without apparent deleterious effects and is well tolerated. Even when hypothermia develops (based on TPA), muscle and rectal temperatures continue to fall.