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.

A case-control study of the congenital hypothyroidism and dysmaturity syndrome of foals.

A case-control study was conducted to identify risk factors for the congenital hypothyroidism and dysmaturity syndrome of foals. A questionnaire was used during personal interviews of foal owners and farm managers to collect information on animal signalment, farm environment, and mare management. Information on 39 foals with the congenital hypothyroidism and dysmaturity syndrome were compared with 39 control foals. Foals with the syndrome had a significantly (P < 0.0001) longer gestation (357.6 d) than control foals (338.9 d). Pregnant mares that were fed greenfeed, did not receive any supplemental mineral, left their "home farm" during gestation, or grazed irrigated pasture had 13.1 (P = 0.0068), 5.6 (P = 0.0472), 4.3 (P = 0.0076), and approximately 15.3 (P = 0.0245), respectively, greater odds of producing an affected foal than mares not experiencing these events. Greenfeed often contains high levels of nitrate (NO3-), which is known to impair thyroid gland function. In light of this, forage samples from participating farms were analyzed for nitrate levels. The odds of one or more congenitally hypothyroid and dysmature foals being born on a farm feeding forage with at least a trace of nitrate was 8.0 times greater (P = 0.0873) than the odds of the disease occurring on a farm that fed forage free of nitrate. Further, the odds of a mare producing an affected foal when fed forage containing at least a trace of nitrate were 5.9 times greater (P = 0.0007) than those of a mare fed nitrate free forage. This study suggests that congenital hypothyroidism and dysmaturity syndrome in foals may be the result of diets that contain nitrate or that are low in iodine being fed to pregnant mares.

Congenital cleft vertebral centrum and intra- and extraspinal cyst in a foal.

A midsagittal centrum cleft of T5-6, malformation and fusion of T3-7, intra- and extraspinal cyst, and myelodysplasia were found in a 3-month-old female Arabian foal that had experienced posterior ataxia since birth. Based on studies in other species, ecto-endodermal adhesions early in embryogenesis leading to formation of an enterogenous cyst is the most probable pathogenesis.

Morphological effects of arthroscopic partial synovectomy in horses.

Gross and microscopic effects of arthroscopic partial synovectomy on synovium and articular cartilage of middle carpal joints were studied in 15 horses. A 7-mm diameter motorized synovial resector was inserted into each middle carpal joint and arthroscopic partial synovectomy and lavage or arthroscopic lavage alone was performed. Study periods were 0 (three horses), 16 (three horses), and 30 days (six horses). No gross evidence of degenerative joint disease was observed at day 16 or 30. At 30 days, resected areas lacked villi and there was deposition of fibrin on the synovial surface with varying amounts of newly formed fibrovascular tissue. Thirty days after arthroscopic synovectomy, normal synovium had not formed in equine middle carpal joints.

Hyperplasia of the thyroid gland and concurrent musculoskeletal deformities in western Canadian foals: reexamination of a previously described syndrome.

A syndrome of neonatal foals characterized by hyperplasia of the thyroid gland and concurrent musculoskeletal deformities (TH-MSD) has been described in western Canada and may be increasing in incidence. In an attempt to improve recognition and understanding of this syndrome, 2946 records of equine abortuses, stillborns, and dead neonatal foals were examined to determine the laboratory involved, the year and month of submission, the breed and sex of the fetus or foal, the type of perinatal loss, the length of gestation, and whether or not the submission had evidence of a lesion of the thyroid gland, the musculoskeletal system, or other abnormal clinical or postmortem findings. One hundred and fifty-four (5.2%) records indicated the presence of an abnormal thyroid gland. Of these, 79 (2.7%) had additional lesions consistent with the TH-MSD syndrome described in the 1980s, while 75 (2.5%) were without these additional lesions. Comparisons among these two groups and a third group of fetuses and foals without lesions of the thyroids glands are described. The results confirm that the TH-MSD syndrome is a specific and unique disease with no breed or sex predilection. It is argued that there may be an "exposure-related" cause, and based on a review of similar disease syndromes of the horse, it is suggested that an examination of the feed is indicated in outbreaks of the TH-MSD syndrome.

Synovial fluid and clinical changes after arthroscopic partial synovectomy of the equine middle carpal joint.

Changes in synovial fluid and clinical variables after arthroscopic partial synovectomy of the middle carpal joint were studied in 12 normal horses. A 7 mm motorized synovial resector was inserted into each middle carpal joint; one middle carpal joint of each horse was randomly selected to have arthroscopic synovectomy (treated) and the opposite joint was lavaged (control). Lameness examinations and synovial fluid analyses were performed before operation and at 8, 14, 21, and 28 days after operation. Lameness variables did not differ between treated and control legs. Middle carpal and carpometacarpal joint circumference measurements were increased for 4 weeks. Synovial fluid specific gravity, pH, total protein, albumin concentration, and alpha-1-, beta- and gamma-globulin concentrations, at 8 and 14 days were significantly higher than before operation in both treated and control middle carpal joints. No significant differences were found between treated and control middle carpal joints at any time for color, clarity, pH, mucin clot formation, total protein, albumin, and globulin fractions. Arthroscopic partial synovectomy and lavage did not cause significant lameness and resulted in a synovitis indistinguishable from synovitis related to arthroscopic lavage alone.

Congenital spinal stenosis and dam mortality associated with feeding moldy cereal straw.

We describe herein an epidemiological investigation of the cause of a syndrome of congenital spinal stenosis (CSS) in four beef herds in western Canada. Three of the herds were affected with the syndrome in 1987, the fourth was affected in 1990. The prevalence of CSS in affected groups of calves varied from 29% (16/55) to 100% (14/14). All affected calves had congenital posterior paralysis or paresis; some calves also had one or more of the following: shortened limbs, forelimb varus deformities, superior brachygnathia, and a dome-shaped cranium. Affected calves showed focal premature closure of axial and appendicular metaphyseal growth plates. At three of the four farms most of the pregnant cows were affected with alopecia with or without pruritus in January, and 25% of the cows in one herd died during the winter. The investigation indicated that CSS was associated with feeding moldy cereal straw to pregnant beef cows during the winter. At all four farms, the cereal straw bales were thoroughly soaked by rain prior to stacking, and obvious mold was present when they were broken open for feeding. Species of both Penicillium and Fusarium were abundant within the bales. The most likely cause of the disease was a fungal mycotoxicosis, although the mycotoxin responsible was not isolated.

Abnormal modelling of trabecular bone in calves.

Lesions due to abnormal modelling of trabecular bone were identified in the femurs of 26 of 55 prenatal and neonatal calves at postmortem examination. Abnormalities included growth retardation lines and lattices, focal retention of primary spongiosa and persistence of secondary spongiosa. The possible cause and pathogenesis of these lesions is discussed. The normal radiographic and histological appearance of the developing bovine femur, during the last four months of gestation, is also described.

Bovine herpesvirus-1-induced pharyngeal tonsil lesions in neonatal and weanling calves.

The potential involvement of the pharyngeal tonsil in the pathogenesis of bovine herpesvirus-1 (BHV-1) infection was examined in neonatal and weanling calves infected by intranasal aerosol. Calves were monitored from days 1 to 5, and on day 6 (neonates) or 8 (weanlings) and, in a second trial at day 4.5, by histology, electron microscopy, immunocytochemistry and virus isolation. Mucosal lesions of neonates were similar to, but less extensive than, those of weanling calves. Loss of microvilli and goblet cells, with minimal epithelial erosions as early as day 1, progressed to necrosis of epithelium and adjacent lymphoid tissue, and leucocyte exudation. Lesions and clinical disease were progressive up to and including day 6 in neonates, but resolving in weanlings on days 5 and 8. By transmission electron microscopy, the physical characteristics of the phagocytic cells appeared similar in both age groups, and viral replication was not identified in leucocytes. Virus was isolated from, or found by immunocytochemistry in, the pharyngeal tonsil of all calves examined, except for two weanlings on days 1 and 8. Virus as detected by immunocytochemistry was restricted to epithelium and superficial lymphoid tissue in neonates, but was found in deep lymphoid tissue around germinal centres in weanlings. The study showed that the pharyngeal tonsil is readily infected with BHV-1 and may be an important lymphoid tissue for early anti-viral responses. The delayed inflammatory response and reduced viral clearance may contribute to the increased susceptibility of neonatal calves to fatal BHV-1 infections.

Tolerance of growing pigs for dietary vitamin A, with special reference to bone integrity.

Weanling crossbred pigs (144) of 8 kg initial weight were fed to 90 kg on diets containing graded levels of vitamin A representing 0, 1, 5, 10, 50 and 100 times the NRC (1988) estimated requirement. No clinical signs of deficiency or toxicity were recorded although plasma and liver retinol levels were affected by treatment. Histopathological examination indicated a high incidence of lesions in the cartilage of the distal femur and ulna, but they were not related to treatment. There was some evidence that excessive vitamin A levels in the diet significantly reduced the uronic acid concentration in joint cartilage, indicating a reduced concentration of proteoglycans. However no relationship was established between dietary vitamin A level and the incidence of clinical osteochondrosis. The results suggest that the allowable range of vitamin A set out in the Canadian feeds regulations is appropriate for practical pig production.

Congenital spinal stenosis in beef calves in western Canada.

Nineteen calves with a clinical history of posterior weakness or ataxia were examined at necropsy. Dorsoventral narrowing of the vertebral canal and myelopathy were found in the thoracic and lumbar areas of the spinal cord; vertebral metaphyseal growth plates had focal areas of premature closure. Malformation of the cranial base and hydrocephalus were also observed. Shortening of long bones and malformation of long bone epiphyses were prominent findings and were associated with focal premature closure of metaphyseal growth plates. The cause of these lesions is unknown; possible causes, including a maternal deficiency of manganese, are discussed.

The effect of exercise on the healing of articular cartilage defects in the equine carpus.

Arthroscopic surgery was performed on 12 horses (2-4 years of age) to create a 7 x 14 mm full-thickness cartilage defect in one radial carpal bone and in the contralateral third carpal bone. Six horses remained confined to a small paddock and six horses underwent a program of increasing exercise consisting of walking, trotting, and cantering for 13 weeks. All lesions showed evidence of healing at week 6 that progressed to more complete healing at week 13. There was no difference in the amount of repair tissue covering the defect. Histologically, the lesions healed with a combination of fibrous tissue and fibrocartilage. The repair tissue was significantly thicker in the exercised horses but there was no difference in repair quality. It was concluded that radial carpal and third carpal lesions have an equal ability to heal and that early postoperative exercise is not detrimental to the repair tissue within these carpal cartilage defects.

Primary intraosseous fibrosarcoma in a cat.

A primary intraosseous fibrosarcoma was diagnosed in a 1.5-year-old cat. Clinical signs included nonweight-bearing lameness of the right forelimb and signs of pain on palpation of the right elbow. Radiography of the right elbow revealed a well-circumscribed osteolytic lesion of the olecranon. The right fore-limb was amputated, and histologic examination revealed tumor invasion into local veins and metastasis to the axillary lymph nodes. The cat had no signs of tumor redevelopment or pulmonary metastatic disease one year after amputation.

Tolerance of weanling pigs for dietary vitamin A and D.

Weanling cross-bred pigs (36 or 48) were caged individually and fed diets containing a supplement of vitamin A (Expt 1) or vitamin D3 (Expt 2) at levels representing 1, 5, 10, 25, 50 and 100 times the NRC (1988) estimated requirements, for 4 weeks. Growth rate, feed intake and feed/gain ratio were not influenced significantly. In Expt 1 the plasma retinol concentrations were at 4 weeks, respectively, 31.7, 39.4, 43.2, 42.9, 44.4, and 46.3 micrograms/dl (P less than 0.05). In Expt 2, the plasma 25(OH)D3 concentrations were at 2 weeks, respectively, 22.5, 29.5, 35.7, 46.2, 79.9, 135.3 ng/ml (P less than 0.001). Histological examination of lung, stomach, kidney, liver and heart indicated no abnormalities, but focal microscopic lesions consistent with osteochondrosis were found in pigs receiving vitamin A at levels over 10 times the requirement. The incidence of osteochondrosis at 2 weeks was, respectively, 0/8, 0/8, 0/8, 0/8, 0/8, and 1/8, and at 4 weeks was, respectively, 0/8, 0/8, 0/8, 2/8, 2/8 and 2/8. The NRC (1988) estimate of the requirement for vitamin D may be somewhat low since the concentration of plasma 25(OH)D was lower with 200 or 1,000 IU vitamin D/kg diet than at the start.

The developmental anatomy of the equine navicular bursa and associated structures.

The navicular bone, navicular bursa and their associated structures were collected from 20 horses ranging in age from 80 days gestation to 2 years post-gestation. The right front foot of every horse was sampled for light microscopy. The development of the navicular bursa and associated structures were studied. Study of the developmental anatomy of the equine navicular bursa established that the bursa is a distinct entity in both the fetus and the adult horse. Development of the bursal cavity in the fetus was found to be complete by 120 days of gestation. Synovial membrane of the navicular bursa was first evident at 100 days of fetal age. With increasing fetal maturation there was a concurrent development in the synovial membrane consisting of increased cellularity, vascularity and villi formation. Nerve fibers or nerve endings were not observed within the synovial membrane of the navicular bursa. However, nerve bundles were often observed within the associated connective tissue, bursal capsule and distal navicular ligament. Pacinian corpuscles were observed in the 200-day fetus in close proximity to the navicular bursa. The development of a fibrous bursal capsule was first evident at 160 days fetal age, thereafter increasing in both thickness and density. Ligaments of the navicular bone were found to develop early in fetal life. At 100 days the collateral sesamoidean ligaments were well developed; however earliest evidence of formation of the distal navicular ligament was at 120 days. In both the fetus and the adult the proximal blood supply to the navicular bone was found to course dorsally in close proximity to the collateral sesamoidean ligament to enter the proximal border of the navicular bone. Concurrent with weight bearing there was a dorsal palmar orientation of the bone trabeculae of the navicular bone. In the young postgestational horses a progressive roughening or fraying of the palmar surface of the navicular bone and the apposing surface of the deep digital flexor tendon was evident.

Dwarfism in a swine herd: suspected vitamin A toxicosis.

Dwarfism was observed in a group of 30 crossbred pigs. Affected pigs had short limbs and retarded growth. Reduced long-bone length as well as flattening and caudal rotation of the humeral head and the distal femoral condyles were seen at necropsy. Metaphyseal growth plates in vertebrae were narrow and, in long bones, were closed prematurely. There was a sparing of growth plates in traction epiphyses. Vitamin A toxicosis was considered as a possible cause.

Effects of lesion size and location on equine articular cartilage repair.

The mechanisms and completeness of equine articular cartilage repair were studied in ten horses over a nine month period. Large (15 mm square) and small (5 mm square) full-thickness lesions were made in weight bearing and nonweight bearing areas of the radiocarpal, middle carpal and femoropatellar joints. The horses were euthanized in groups of two 1, 2.5, 4, 5 and 9 months later. Gross pathology, microradiography, and histopathology were used to evaluate qualitative aspects of articular repair. Computer assisted microdensitometry of safranin-O stained cartilage sections was used to quantitate cartilage matrix proteoglycan levels. Structural repair had occurred in most small defects at the end of nine months by a combination of matrix flow and extrinsic repair mechanisms. Elaboration of matrix proteoglycans was not complete at this time. Statistically better healing occurred in small weight bearing lesions, compared to large or nonweight bearing lesions. Synovial and perichondrial pannus interfered with healing of osteochondral defects that were adjacent to the cranial rim of the third carpal bone. Clinical and experimental experience suggests that these lesions are unlikely to heal, whereas similar lesions in the radiocarpal and femoropatellar joints had satisfactory outcomes. Observations made in this study support the use of early postoperative ambulation, passive flexion of operated joints, and recuperative periods of up to a year for large cartilage defects.