Scapulohumeral arthrodesis in four Shetland ponies

Four Shetland ponies were presented with severe osteoarthritis of the scapulohumeral joint to the Faculty of Veterinary Medicine of Ghent University over a period of 4 years. Ponies were treated with internal fixation using locking compression plates (LCPs) applied cranially across the scapulohumeral joint. Although two ponies developed mild complications, all ponies were more comfortable in the limb within a few hours following arthrodesis.     

Scapulohumeral arthrodesis in miniature horses

OBJECTIVES: To describe surgical arthrodesis of the scapulohumeral joint and to evaluate its efficacy in reducing morbidity associated with severe shoulder dysfunction in miniature horses. STUDY DESIGN: Retrospective study. ANIMALS: Four miniature horses. METHODS: Medical records and radiographs were reviewed for history, physical examination findings, lameness evaluation, radiographic evaluation, surgical techniques, postoperative complications, and outcome. A 10- or 11-hole, 4.5-mm narrow dynamic compression plate and 4.5-mm cortical screws were applied to the cranial surface of the scapula and cranial surface of the humerus after osteotomy of the intermediate tubercle. In most horses, 1 or 2 screws were inserted in lag fashion across the joint, through holes in the plate. RESULTS: Scapulohumeral osteoarthritis was diagnosed radiographically in 4 horses, and 3 horses had concurrent shoulder luxation or subluxation. All horses had grade 3 or 4 lameness before surgery, and most improved by 1 to 2 grades after surgery. Despite complications of implant failure (2 horses), infection (2 horses), scapular fracture (1 horse), and atrophy of the shoulder muscles (1 horse), functional arthrodesis reduced morbidity in all horses. CONCLUSIONS: Scapulohumeral arthrodesis facilitates early return to weight bearing in miniature horses with severe scapulohumeral joint osteoarthrosis. Despite functional gait abnormality, the horses ambulated quite well after surgery. CLINICAL RELEVANCE: Scapulohumeral arthrodesis should be considered for debilitating conditions of the shoulder joint in miniature horses, especially when the intended outcome is breeding or pasture soundness.     

Risk factors for insect bite hypersensitivity in Friesian horses and Shetland ponies in The Netherlands

Insect bite hypersensitivity (IBH) is an equine skin allergy caused by bites of Culicoides spp. and impacts on the welfare of affected horses. The aim of this study was to identify and quantify risk factors for IBH. Data from 3453 Friesian horse mares and 7074 Shetland pony mares scored for IBH by inspectors during obligatory foal inspections were analysed using breed-specific multivariable logistic regression models. The combined effect of month and year of scoring, Province and inspector were significantly associated with IBH in both breeds. In Shetland pony mares, withers height and coat colour were also significantly associated with IBH, while body condition had a nearly significant effect. The outcomes from this study on risk factors might contribute to the development of more efficient measures to reduce the prevalence of IBH.     

Equine serum lipids: serum lipids and glucose in Morgan and Thoroughbred horses and Shetland ponies.

Concentrations of serum phospholipids, triglycerides, total cholesterol, nonesterified fatty acids, and glucose were determined for 9 months (September, 1972, to May, 1973) in 19 fasting horses and ponies (8 Morgan horses, 7 Thoroughbred horses, and 4 Shetland Ponies). Morgan horses had higher concentrations of total lipid than did Thoroughbreds, although the relative proportions of each type of lipid were similar in the 2 breeds. Shetland Ponies had higher nonesterified fatty acid and lower glucose concentrations than did either breed of horse. In both breeds of horses, concentrations of serum triglycerides in the cold months (December to March) were lower than those in the warm months. In the Shetland Pony, there was no seasonal variation in triglycerides, but a significant increase was seen in concentration of nonesterified fatty acids in the cold months. The significance of these findings is discussed.     

Ovarian, uterine and embryo dynamics in horses versus ponies

Characteristics of the internal genitalia were compared between horses and ponies contemporaneously in a single study by asingle operator. Diameter of the preovulatory follicle for 10 days before ovulation (Day 0) and cross-sectional area of the corpus luteum for 10 days after ovulation were measured in 12 horses and 12 ponies. Follicle growth rate and maximum diameter attained during growth and luteal tissue area were not different between mare types. However, ultrasonic echogenicity of luteal tissue was less on Day 0 (P<0.09) and Day 1 (P<0.01) in ponies than in horses, suggesting that under field conditions mare type should be considered when using the extent of luteal gland echogenicity for estimating the number of days postovulation and luteal function. Circulating concentrations of progesterone averaged over Days 3 to 10 were greater in ponies (10.3 ng/ml) than in horses (8.7 ng/ml) as suggested by a tendency (P<0.1) towards a type-by-day interaction.Luteal, uterine and embryonic characteristics during Days 0 to 40 of pregnancy were compared between 7 horses and 9 ponies. Luteal tissue area of the primary corpus luteum was not different between mare types during Days 0 to 30 and during luteal resurgence after Day 30. The interaction between mare type and day was significant for circulating progesterone concentrations; the interaction seemed to result primarily from higher progesterone levels in ponies during Days 6 to 12 and Days 34 to 40. Progesterone concentrations were about 25% higher in ponies on the approximate days that levels were at their highest in the two types of mares. These results indicate, a need for further studies on the effect of mare size or type on circulating concentrations of progesterone, and the consideration of size or type in clinically evaluating progesterone levels in pregnant mares. Apparent partial recovery of the corpus luteum of the previous estrous cycle occurred during early pregnancy in one pony.Increasing diameter of the embryonic vesicle and the extent of uterine tone were similar between horses and ponies. Although diameter of the uterine horns decreased in parallel for the two mare types during Days 0 to 40, the diameter was significantly less (2.2 mm difference averaged over all days) for ponies than horses. The temporal relationship between an expanding embryonic vesicle concurrently with decreasing uterine horn size and enhanced uterine turgidity is compatible with the postulated mechanism of embryo fixation. The smaller uterus in ponies with no difference in size of the conceptus between mare types could account for earlier fixation of the embryonic vesicle in ponies than in horses.     

Apneic oxygenation in anesthetized ponies and horses

Apneic oxygenation was studied in six ponies for 30 minutes, and six horses for 10 minutes. Arterial blood was sampled at regular intervals for measurement of oxygen and carbon dioxide tensions (PaO₂ and PaCO₂) and calculation of alveolar-arterial oxygen tension difference (PAO₂-PaO₂). In both groups of animals, PaO₂ decreased rapidly during the first 3 minutes of apnea, then more slowly. Although the mean value was above 100 mmHg at 10 minutes, there was considerable inter-animal variability. Before apnea, PAO₂-PaO₂ was slightly, but not significantly, larger in horses than in ponies and increased in both groups during the first 3 minutes of apnea, after which the increase was slower. There was no significant difference between ponies and horses up to 10 minutes, suggesting that PAO₂-PaO₂ is independent of body size. In ponies, the PAO₂-PaO₂ did not change significantly between 10 and 30 minutes. Final PaO₂ could not be correlated with initial PaO₂ or initial PAO₂-PaO₂. The rate of rise of PAO₂-PaO₂ could not be predicted from baseline values. The rate of rise of PaCO₂ was similar and fairly constant in ponies and horses, and did not contribute to the rapid initial decrease in PaO₂. It appears that apneic oxygenation should not be used in the equine species, since it is impossible to predict in which animals the technique is safe for more than a few minutes.     

Current concepts of hyperlipaemia in horses and ponies

Hyperlipaemia is an important condition in ponies, not just because of the seriousness of the clinical signs and biochemical changes involved, but because of the distress it causes owners and breeders that have had animals suffer from it. Hyperlipaemia occurs most commonly in fat ponies in late pregnancy and is rarely seen in larger horses. The syndrome has similarities with conditions in other species but the definitive aetiologies are not yet known. The condition in ponies is undoubtedly related to stress. The biochemical mechanisms involved in equine hyperlipaemia are considered and an hypothesis of possible pathogenesis is put forward. This hypothesis is tested by presenting the results of a preliminary study to evaluate glucose and lipid metabolism in horses and ponies. It appears that the pony is markedly insensitive to insulin compared to larger horses which means that triglycerides are more readily mobilised and the animal is therefore susceptible to hyperlipaemia in a situation of negative energy balance. The effect of stress is to increase cortisol levels which only exacerbates the insulin insensitivity and so creates a vicious circle. The importance of an innate insulin insensitivity may also be important in the pathogenesis of such conditions as laminitis.     

Radiological study to evaluate suspected scapulohumeral joint dysplasia in Shetland ponies

A radiological study was performed to test the hypothesis that osteoarthritis of the scapulohumeral joint in Shetland ponies is secondary to shoulder dysplasia. Animals were selected into 3 groups: Group 1: Shetland ponies with a radiological and clinical diagnosis of scapulohumeral osteoarthritis (n = 8); Group 2: Shetland ponies without forelimb lameness (n = 12); Group 3: Horses/ponies without a history or clinical signs of forelimb lameness (n = 22). Anatomical indices were measured from mediolateral radiographs of a scapulohumeral joint from each animal. There was a significant difference in the mean radius of curvature of the glenoid cavity of the scapula (RCG) between the 3 groups (MANOVA test, P = 0.003). The mean RCG of both Group 1 (P = 0.001) and Group 2 (P = 0.022) was significantly greater than that of Group 3. There was no significant effect of group on the radius of curvature of the humeral head or on the Conformity Index. There was a significant effect of group on the Glenoid Ratio (MANOVA test, P = 3 x 10(-6)). The mean Glenoid Ratio was significantly lower in both Group 1 (P = 2 x 10(-6)) and in Group 2 (P = 0.006) than in Group 3. These results indicate that the glenoid cavity of the scapula is 'flatter' and 'shallower' in Shetland ponies which we postulate to be a primary dysplasia in this breed.