Quarter Horse Foals Research Articles

Correlative study of defective cartilage and bone growth in foals fed a low‐copper diet

SummaryA blind randomised study using two groups of age‐ and sex‐matched Quarter Horse foals was conducted by feeding a low copper diet containing 8 ppm of copper (Cu) and a control diet containing 25 ppm. Foals in the low‐Cu group had declining liver Cu values and developed osteochondritis (OCD), epiphysitis and limb deformities over a 6‐month period. Erosion and separation of cartilage from the subchondral bone in the dorsal facets of the cervical spine were the most consistent post‐mortem lesions. Foals fed the high‐Cu diet had no significant musculoskeletal lesions. Scoring of standing lateral cervical radiographs was a moderately sensitive (0.68) and specific (0.70) test and had moderate agreement with post‐mortem findings (κ = 0.35). Technetium scintigraphy of the limbs and cervical spine failed to detect occult or known lesions in the limbs and cervical spine. Microscopic examination of growth plates and metaphyseal bone from affected foals showed that fractures disrupted or displaced the normal growth plate architecture and interfered with orderly bone growth, similar to Cu deficiency in cattle. Bone morphometry indicated there was less subchondral bone volume in the distal cannon bone (P<0.005). Similarly, there were fewer newly formed trabeculae in the primary spongiosa (P<0.02) and metaphysis (P<0.07) of the distal tibia in the Cu‐deficient foals. Biochemical studies were limited to 4 control and 6 low‐Cu foals. Of the 6 low‐Cu foals, 4 were severely affected with multiple lesions. These assays showed significantly reduced collagen cross‐linking in the cartilage and bone articular cartilage of severely affected foals. The control group foals had articular and growth plate cartilage explants in tissue culture released increased amounts of gelatinase and proteoglycanase, reflecting increased matrix remodelling. Traditional concepts of osteochondritis have implicated a non‐specific defect in endochondral ossification. This study proposes a relationship between low copper intakes in fast‐growing horses, inferior collagen quality, biomechanically weak cartilage and OCD lesions. While all foals in the low‐Cu group were affected, only 5 of the 9 developed clinically significant lesions. This indicates that factors other than nutrition, such as individual variation in growth rate or genetic potential, still influence the expression of this syndrome.

Respiratory stridor associated with polymyopathy suspected to be hyperkalemic periodic paralysis in four Quarter Horse foals

Respiratory stridor associated with polymyopathy suspected to be hyperkalemic periodic paralysis in four Quarter Horse foals

Use of orthopedic markers for quantitative determination of proximal radial and ulnar growth in foals

Summary Cortical bone screws were implanted into the proximal portion of the right and left radius and ulna of 6 newborn Quarter Horse foals as radiographic markers for measurement of growth. Distance between markers on a lateral radiographic view was measured. Radiographs were taken at 2-week intervals until the horses were 8 weeks old, at 4-week intervals until they were 48 weeks old, and at 12-week intervals until they were 72 weeks old. The proximal radius and ulna grew at similar rates during the 72-week period of evaluation, and growth continued throughout 72 weeks. The proximal radius grew 3.5 cm, and the ulna grew 3.4 cm. Although the rates of growth were similar, growth from the ulnar physis contributed only to the length of the olecranon; growth was not transmitted to the ulnar diaphysis distal to the cubital joint. The proximal radius slid distally in relation to the ulna as growth occurred at the proximal radial physis. These findings suggest that transfixing the ulna to the radius while growth is occurring at the proximal radial physis impedes the natural shifting process, and subluxation of the elbow can result. Severity of subluxation would be inversely related to the age of the horse at the time of transfixation.

Hematologic development in foals receiving intravenous iron supplementation

Seventeen healthy Thoroughbred and Quarter Horse foals were divided into control (n=8) and treated (n=9) groups and studied from birth until 4 months of age. Foals in the treated group were intravenously injected with an experimental drug containing 0.4 g of iron in the form of a polynuclear complex of carbohydrate and ferric hydroxide on days 7, 14, 21 and 28, for a total dosage of 1.6 g of iron. Foals had access to Bermuda grass hay and Bahia pasture. A creep feed formulated with no trace mineral supplement was provided after two months of age. Hemoglobin concentration, hematecrit, erythrocyte counts, mean cell volume, microcyte numbers, plasma protein, fibrinogen, total leucocyte count, serum iron, total iron binding capacity and serum ferritin values were determined at 8 different ages. On the basis of analysis of variance at P<0.05, no significant differences were found between groups for any of these parameters, however, there were changes in parameters over time in both groups. A discussion of results and possible interpretations follows.

A XERORADIOGRAPHIC STUDY OF OSTEOCHONDROSIS IN THE METACARPOPHALANGEAL REGION OF TWO FOALS

Using xeroradiographic techniques, both metacarpophalangeal regions of six quarter horse foals were radiographed at 1 day of age and at 2-week intervals until they were 6 weeks old, and then at 4-week intervals until they were 12 months old. Lateromedial and dorsopalmar xeroradiographs of each metacarpophalangeal region were made per examination; dorsomedial-palmarolateral projections of the left metacarpophalangeal joint of foal 6 were also made. The foals were weighed and measured at the withers immediately prior to each examination. Representative xeroradiographs were selected to demonstrate progression of the osteochondrosis (OCH) lesions in two of these foals. Radiographic evidence of osteochondrosis in the metacarpophalangeal region was first detected at 10 weeks and followed through 12 months of age. In one foal the lesions were bilaterally symmetric and involved the dorsoproximal aspect of the sagittal ridge of metacarpal 3; in the other, the left medial proximal sesamoid bone was affected. One of the sagittal ridge lesions progressed to osteochondritis dissecans by 26 weeks; the other sagittal ridge lesion and that of the sesamoid bone healed spontaneously, but residual radiographic evidence of the disease persisted throughout the study in both foals.

A XERORADIOGRAPHIC STUDY OF THE DEVELOPING QUARTERHORSE FOREDIGIT AND METACARPOPHALANGEAL REGION FROM SIX TO TWELVE MONTHS OF AGE

The purpose of the project was to provide a reference for radiographic anatomy of the developing equine foredigit and metacarpophalangeal region. Using xeroradiographic techniques, both foredigits and metacarpophalangeal regions of six Quarter Horse foals were radiographed at 1 day of age and then at 2‐week intervals until the foals were 6 weeks old. The foals were then radiographed at 4‐week intervals until they were 12 months old. The period from birth to 6 months has been described in a previous report. This paper deals with the period from 6 to 12 months of age. Lateromedial and dorsopalmar xeroradiographs of each foredigit and metacarpophalangeal region and a dorsal 65° proximal‐palmarodistal oblique view of the distal part of the digit were made at each examination. Foals were weighed and were measured at the withers immediately prior to each examination. Representative xeroradiographs were selected and appropriately labeled to demonstrate normal radiographic anatomy of these regions. Earliest radiographic visualization of distal epiphyseal ossification in metacarpal 2 and metacarpal 4 was extremely variable and ranged from 4 to 38 weeks. It was not possible to determine accurately the ages at which distal physes of the small metacarpal bones closed. In one foal, three of four of these physes were closed at 26 weeks, while in another foal, none had closed when last radiographed at 54 weeks. Radiographic closure of the proximal physis of the middle phalanx ranged from 18 to 30 weeks (mean = 26 weeks). Radiographic closure of the proximal physis of the proximal phalanx ranged from 22 to 38 weeks (mean = 30 weeks). Radiographic closure of the distal physis of metacarpal 3 ranged from 18 to 38 weeks (mean = 29 weeks).

SCINTIGRAPHIC CHARACTERIZATION OF THE EQUINE FOREDIGIT AND METACARPOPHALANGEAL REGION FROM BIRTH TO SIX MONTHS OF AGE

Both foredigits and metacarpophalangeal joints of six Quarter Horse foals were scanned serially to six months of age using 99Tc‐methylene diphosphonate. Dorsal scans were made on day 1 and at two, four, six, ten, 14, 18, 22 and 26 weeks of age. Scans were assessed visually for distal third metacarpal, proximal phalangeal, and middle phalangeal physeal appearance and closure. Scans were also evaluated by computer region‐of‐interest (ROI) and line‐profile analysis to characterize the physes quantitatively. Physeal region radioactivity relative to a disphyseal reference region was greatest at four weeks for all physes. Scintigraphic physeal closure of all physes occurred at approximately six months of age with a range of four and one half to greater than six months. The study was conducted to allow better assessment of diffuse and focal physeal disease by determining developmental times at which normal physeal region radioactivity has decreased enough to not obscure abnormal radioactivity and by quantifying scintigraphic physeal appearance which enables computer analysis to detect visually indeterminate physeal abnormalities.

A XERORADIOGRAPHIC STUDY OF THE DEVELOPING EQUINE FOREDIGIT AND METACARPOPHALANGEAL REGION FROM BIRTH TO SIX MONTHS OF AGE

The purpose of the project was to provide a reference for radiographic anatomy of the developing equine foredigit and metacarpophalangeal region. Using xeroradiographic techniques, both foredigits and meta‐carpophalangeal regions of six Quarter Horse foals were radiographed at one day of age and at two‐week intervals until the foals were six weeks old. The foals were then radiographed at four‐week intervals until they were 12 months old. This report deals specifically with the first six months of postnatal development. Lateromedial and dorsopalmar xeroradiographs of each foredigit and metacarpophalangeal region and a dorsal 65° proximal‐palmarodistal oblique view of the distal part of the digit were made for each examination. The foals were weighed and measured at the withers immediately prior to each examination. Representative xeroradiographs were selected and appropriately labeled to demonstrate normal radio‐graphic anatomy of these regions. First radiographic appearance of distal epiphyseal ossification in metacarpal 2 and metacarpal 4 was extremely variable and ranged from four to 38 weeks. Radiographic closure of the proximal physis of the middle phalanx ranged from 18 to 30 weeks (mean = 26 weeks). Radiographic closure of the proximal physis of the proximal phalanx ranged from 22 to 38 weeks (mean = 30 weeks). Radiographic closure of the distal physis of metacarpal 3 ranged from 18 to 38 weeks (mean = 29 weeks). When xeroradiographic physeal closure times were compared with scintigraphic closure times from a companion study, results correlated very well. A crena marginis solearis was observed in ten of 12 forelimbs (83.3%); its first radiographic appearance ranged from four to 22 weeks (mean = 11–12 weeks). A consistent groove in the hoof wall, which formed near the time of birth and moved distally at about 3 mm per week, was noted. The groove's distance from the proximal hoof border may be useful in age estimation of foals less than 18–20 weeks old.

The effects of fixation of the ulna to the radius in young foals.

The effects of radioulnar fixation were studied in 21 Quarter horse foals by applying a bone plate to the caudal aspect of the proximal part of the ulna, with screws engaging both the radius and the ulna. The plates were applied at 1 month of age in six foals (group I), 5 months of age in six foals (group II), and 7 months of age in three foals (group III). Six foals underwent sham operations at 1 month of age to serve as controls (group IV). Ulnar dysplasia and elbow subluxation developed in all treated foals. The magnitude of ulnar dysplasia was inversely related to the patient's age at fixation and was accompanied by degenerative joint disease and lameness in foals undergoing fixation at 1 and 5 months of age. Removal of the fixation appliances 16 weeks after implantation in three foals from each of groups I and II failed to reverse the degree of ulnar dysplasia. Although foals undergoing fixation at 7 months of age (group III) were not lame, radiographic evidence of subluxation and subtle degenerative changes in the articular cartilage of the treated elbow did develop. Recommendations for avoidance of radioulnar fixation were developed from these observations.

Umbilical blood flow and the effects of premature severance in the neonatal horse

Thirteen randomly assigned Quarter Horse foals were used in a study to determine the presence of umbilical blood flow immediately post partum and to determine if premature severance of the umbilical cord would alter significantly the hematology of the horse neonate. Packed cell volume (PCV), mean corpuscular volume (MCV), mean corpuscular hemoglobin concentration (MCHC), hemoglobin concentration (Hgb), red blood cell count (RBC), plasma protein (PP), and heart and respiratory rates were determined every 30 min for the first 6 h of life for both control and treated foals. Control foals had their umbilical cords measured for the presence of umbilical blood flow. Treated foals had their umbilical cords separated after birth and any free flow of blood collected and a volume measure determined. The umbilicus was separated within 10 sec post partum. No blood flow was detected in the control group of foals within 2 min post partum. The blood obtained from the separated umbilicus of the treatment group measured less than 125 cc. PCV, MCV, MCHC, Hgb, RBC, and PP were not significantly different between the two groups (P > 0.05). Except for MCHC and PP, all parameters studied decreased over the first 6 h of life. Heart rate and respiration rates did not significantly differ from each other (P > 0.05) and decreased over the first 6 h of life.

The effect of artificial rearing on the growth of foals.

Fourteen Quarter Horse foals were used to evaluate the effects of artificial rearing on growth. Seven foals were removed from their dams at 3 d of age and fed a reconstituted 26% crude protein (CP) milk replacer free choice for 1 mo, at which time ad libitum solid feeding began. Controls were weaned from their dams at 2 mo of age and fed a 21% CP concentrate ad libitum until the end of the trial. Variables measured during the 26-wk trial were live body weight, height at the withers and length of body from point of shoulder to point of hip. No significant differences were found between the two groups, except during wk 8 where 2-mo weaned foals were slightly heavier (P less than .10). Average daily gains for artificially reared and 2-mo weaned foals were .95 and .98 kg, respectively.

Haematology of foals up to one year old

Packed cell volume, haemoglobin concentration, erythrocyte counts, erythrocyte indices, serum iron, iron binding capacities, total and differential leucocyte counts, platelet counts, total plasma protein, fibrinogen, haptoglobin and icterus index values were determined at 14 different ages in eight Thoroughbred and 14 Quarterhorse foals during the first year of life. Absolute neutrophil numbers in blood decreased and lymphocyte numbers increased during the first months. Absolute eosinophil numbers tended to increase until three months old. Haemoglobin concentration and packed cell volume decreased significantly during the first two weeks and generally stayed in the lower portion of adult horse normal ranges during the remainder of the first year. Mean cell volume decreased to minimum values at approximately four months and then gradually increased. Serum iron was high at birth and decreased rapidly to a minimum at three days old. Total iron-binding capacity increased to a maximum at one month. Serum haptoglobin was generally within the adult normal range at birth. A moderate, but significant, decrease occurred at one week old. Fibrinogen concentration increased to a maximum at five months. Icterus index values decreased rapidly during the first two weeks of life. Minor changes occurred in other parameters measured. Possible causes for the various changes in haematological parameters are discussed.

Bilateral multiple congenital ocular defects in Quarterhorse foals

Bilateral multiple congenital ocular defects in Quarterhorse foals

Congenital internal hydrocephalus in a quarter horse foal

Since the normal absorption of CSF occurs in the cerebral veins and venous sinuses, any obstruction to the normal flow and absorption of CSF will result in accumulation of CSF central to the site of obstruction. Such accumulation within the cranium is defined as hydrocephalus. A foal was presented with an enlarged and an abnormally-shaped skull, but with normal behavior. The filly's condition deteriorated. Radiographs showed a domeshaped cranial vault with compression of the frontal sinus region. Massive hydrocephalus with little normal cerebral tissue left was diagnosed with ultrasound. Surgery was attempted to relieve the pressure. Eventually the foal was euthanized. Post-mortem confirmed the radiographic and ultrasound diagnosis. Since there was a lack of demonstrable obstruction, the authors suspected the foal had suffered from the Arnold-Chiari syndrome.

Naturally-occurring Tyzzer's disease (Bacillus piliformis infection) in horse foals.

Spontaneous Tyzzer's disease is described in quarter horse foals which died suddenly with no clinical history of apparent illness. Significant gross findings included icterus, focal paletan areas in the liver and catarrhal entercolitis. Focal dark red lesions were present in the small intestine of one foal, and the mesenteric lymph nodes of another were enlarged and hyperemic. Histopathologically, the liver showed multiple discrete and confluent foci of necrosis, fatty change, sinusoid congestion and haemorrhage. Bundles of intracytoplasmic bacilli were demonstrated in hepatocytes at the margin of liver lesions using special stains. Infiltration of the portal triads with inflammatory cells and biliary duct hyperplasia and degeneration were also observed. Lesions in the intestine were characterised by mucosal necrosis with inflammatory cell infiltration, increased mucus production, submucosal lymphoid hyperplasia and, in one foal, submucosal haemorrhage. Necrosis of lymph follicles, congestion and haemorrhage were also present in the spleen and mesenteric lymph nodes.

Experimental Infection of Strongyloides westeri in Parasite-Free Ponies

The prepatent period of Strongyloides westeri experimental infection in ponies was 6 to 10 days in pony foals and 11 to 13 days in pony yearlings. The infection stimulated moderate inflammation in the anterior one-third of the small intestine in pony foals. Pony yearlings and Quarter Horse foals lost the infection and were resistant to reinfection. The loss of infection was associated with a neutrophilia in Quarter Horse foals and an increase in p-globulin in pony yearlings. Strongyloides westeri is a parasite of the young foal. Poynter (1970) reported that eggs may first appear in the feces of foals from 1 to 22 weeks of age but the actual prepatent period has not been determined. There is general agreement that the infection is limited, and that the host becomes resistant to reinfection (Poynter, 1970; Russell, 1948; Salisbury et al., 1940; Todd et al., 1950). This parasite is the reported cause of diarrhea (Fried et al., 1956; Salisbury et al., 1940), emaciation (Galliard, 1967), and death (Davidson, 1943). These observations on the pathogenesis of S. westeri were made on naturally infected animals. The first reported experimental infection with S. westeri (Bello et al., 1973) was accomplished by cutaneous exposure. Lyons et al. (1973) have also experimentally infected foals by administering larvae through a stomach tube or by cutaneous ex-