Suspensory ligaments (SL) from 32 Thoroughbreds and 32 Standardbreds were collected to evaluate the variation in muscle content with respect to age, breed, sex, limb, and use. Six transverse sections, each 3 to 5 mm thick, were obtained from each SL. Four sections were taken from the body of the SL and 1 from the midportion of each branch. Sections were stained with van Gieson picric acid-fuchsin solution, then photographed, and black-and-white slides were made from the processed negatives. The transverse-sectional area of the SL and the contained muscle were determined by use of a computer with a color monitor and a digitizing device with its associated software. The percentage of muscle was then calculated for each section, for the entire ligament, and for each horse. Results were analyzed by multiple-regression analysis and Duncan multiple-range test, using the General Linear Model of SAS. Standardbreds had 40% more muscle in their SL than did Thoroughbreds. There was no significant difference in the percentage of SL muscle among sex, age, use, individual limb, or forelimb vs hind limb. For Standardbred horses, females had significantly greater muscle area content than intact males. Also, hind limb muscle area content was significantly greater than forelimb muscle content. Thoroughbred horses between 2 and 10 years of age not in training had significantly more muscle content than horses of the same age not in training. The reasons for these differences remain unclear.

Recordings of visual-evoked potentials that were induced by flashes of white light were obtained from 13 Beagle pups to document the development of the response from age 7 to 100 days. Responses were recorded between needle electrodes placed on the nuchal crest and the interorbital line, with ground at the vertex. Five alternating positive (P) and negative (N) peaks were observed in most visual-evoked potentials: P1, N1, P2, N2, and P3. Responses were recorded from 2 pups prior to opening of the eyelids. Recordings were performed without sedation or dark adaptation. Peak latencies were essentially mature (equal to those of adult dogs) by day 11 for P1, and by day 38 for N1, and P2. The latencies to N2 and P3 did not reach adult values by day 100, but did reach plateau values by day 43. The P1-N1, amplitude measurements reached mature levels by day 14, whereas N1-P2 amplitudes were mature by day 32. The P2-N2 and N2-P3 amplitudes reached plateaus that greatly exceeded adult amplitudes by days 50 and 58, respectively. Maturation of visual-evoked potential responses paralleled reported morphologic development of the visual cortex. All of the measured latency and amplitude values had significant (P less than or equal to 0.004) linear regression lines of latency vs age or amplitude vs age.

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.

Ceruloplasmin (Cp) was isolated from fresh equine plasma by precipitation, cellulose chromatography, and improved ion-exchange chromatography. Purified equine Cp is a glycoprotein having a molecular weight of approximately 115,000. In electrophoresis, equine Cp migrated to the alpha 1-globulin region, its isoelectric point was about 4.15 and consisted of about 890 amino acid residues. Serum Cp concentration was measured by use of the single radial immunodiffusion method. In clinically normal horses, the mean (+/- SD) serum Cp concentration of newborn foals was 2.87 +/- 0.40 mg/ml and that of 3-month-old foals was 5.02 +/- 0.92 mg/ml, which was similar to the adult value. It reached a peak of 6.06 +/- 0.74 mg/ml in 2-year-old horses. The Cp concentration in mares was not statistically different for the perinatal period, but it decreased immediately before and after delivery. Concentration of Cp increased at 6 days after IM administration of turpentine oil, castration, or jejunojejunostomy in adult horses, and increased to peak values twice as high as baseline values at 7 to 14 days, returning to baseline values at 28 days after treatment. We concluded that equine serum Cp is an acute-phase reactive protein increased in the intermediary or later phase of acute inflammation.

Epidemiologic data were evaluated from all dogs admitted to the University of Minnesota, Veterinary Teaching Hospital (UMVTH) between June 1981 and November 1989. Of 69,890 admissions, 2,077 were Miniature Schnauzers. Uroliths were retrieved from 63 of the 2,077 Miniature Schnauzers admitted. In 20 of the 63 urolith episodes, calcium oxalate was the predominant mineral identified. By comparison, calcium oxalate uroliths were identified in only 56 of the remaining 67,813 non-Miniature Schnauzer canine admissions. The odds that uroliths from Miniature Schnauzers were composed of calcium oxalate was 11.8 times greater than for other canine breeds evaluated at the UMVTH (95% confidence interval = 6.8 to 20.1). Data also were evaluated from files of uroliths retrieved from dogs and submitted to the Minnesota Urolith Center for quantitative mineral analysis between June 1981 and November 1989. Of 3,930 uroliths analyzed, 615 (15.6%) uroliths were obtained from Miniature Schnauzers. Of the 615 uroliths, 175 (28.4%) were calcium oxalate. By comparison, only 550 (16.6%) of the remaining 3,315 from dogs of breeds other than Miniature Schnauzers were calcium oxalate. The odds that uroliths submitted for analysis were composed of calcium oxalate was 2 times greater for Miniature Schnauzers than for dogs of other breeds (95% confidence interval = 1.6 to 2.4). Calcium oxalate uroliths were retrieved more frequently in males than females. The risk for males developing calcium oxalate uroliths was > 3 times the risk for females in both groups of data evaluated. The mean age of all Miniature Schnauzers admitted to the UMVTH with calcium oxalate uroliths was 9 years. Calcium oxalate uroliths were not detected in Miniature Schnauzers younger than 1.7 years.

The third carpal bone (C3) was collected from both forelimbs of 27 Thoroughbreds. On the basis of age, training, and history, specimens were assigned to 1 of 5 groups: yearling, untrained horses (group 1, n = 4); 2- to 3-year-old, untrained horses (group 2, n = 7); trained 2-year-old horses (group 3, n = 6); trained 3-year-old horses (group 4, n = 6); and 3-year-old, trained horses with carpal pathologic features (group 5, n = 4). A transverse section of subchondral bone 5-mm thick was cut in a precise fashion 10 mm below the proximal articular surface of all specimens. After high-detail radiography was done, indentation testing was performed on the proximal surface of the section at points 5 mm apart. The stiffness of the subchondral cancellous bone was determined from the slope of the load vs displacement curve. Topographic plots of stiffness measurements were compared with radiographs of each specimen. Point determinations were averaged to derive measures for the radial and intermediate facets, and for regions 5, 10, 15, and 20 mm from the dorsal margin of C3. Area fraction (1-p; p = porosity) was measured for the radial and intermediate facets, using an automated image analysis system. Significant (P < 0.05) increases in stiffness and area fraction were found in the C3 from trained horses (groups 3 to 5), compared with untrained horses (groups 1 to 2). Stiffness and area fraction of the radial facet of pathologic C3 were significantly higher than the same variables measured in C. from any other group. A typical profile of regional subchondral stiffness was identified in C3 from normal horses, with maximal stiffness measured 10 mm from the dorsal articular margin. A different pattern was found in pathologic C3, with significantly greater stiffness 15 and 20 mm from the dorsal articular margin when compared with normal horses. A highly significant (P < 0.0001) direct linear correlation between stiffness and area fraction at the radial facet was found. Topographic and radiographic analysis demonstrated good correlation between stiffness and radiographic density of the bone sections. The observed patterns of normal and pathologic C3 were contrasted. In particular, a large gradient in sub-chondral stiffness was identified in pathologic C3 at the dorsomedial aspect of the bone.

The effect of age on the pharmacokinetics of chloramphenicol was determined after IV administration of chloramphenicol sodium succinate (25 mg/kg of body weight) to 6 foals at 1 day and 3, 7, 14, and 42 days of age. The disposition of chloramphenicol was best described, using a two-compartment open model in all foals at all ages evaluated. Significant age-related changes were observed in values for the major kinetic terms describing the disposition of chloramphenicol in foals; the greatest changes were observed between 1 day and 3 days of age. The mean +/- SD value for elimination rate constant (beta) for chloramphenicol in 1-day-old foals (0.131 +/- 0.06 h-1) was significantly (P < 0.005) lower than the value in 3-day-old foals (0.514 +/- 0.156 h-1), and both values were significantly (P < 0.005) lower than values for beta in 7-, 14-, and 42-day-old foals. With increasing age, the increase in the mean value for beta resulted in decrease in the harmonic mean elimination half-time (t1/2 beta) for chloramphenicol, from 5.29 hours in 1-day-old foals to: 1.35 hours in 3-day-old foals; 0.61 hour in 7-day-old foals; 0.51 hour in 14-day-old foals; and 0.34 hour in 42-day-old foals. At 1, 3, and 7 days of age, values for t1/2 beta of chloramphenicol in a premature foal born after parturition was induced with oxytocin, were considerably longer than comparable t1/2 beta values for term foals born naturally. The mean body clearance (ClB) of chloramphenicol in 1-day-old foals (2.25 +/- 0.67 ml/min.kg of body weight) was significantly lower than values in: 3-day-old (6.23 +/- 2.22 ml/min.kg; P < 0.05); 7-day-old (8.86 +/- 1.90 ml/min.kg; P < 0.0005); 14-day-old (9.63 +/- 1.63 ml/min.kg; P < 0.0005); and 42-day-old (9.68 +/- 2.76 ml/min.kg; P < 0.0001) foals. In foals of all ages, ClB of chloramphenicol in the parturition-induced premature foal was lower than the mean value for term foals born naturally. The volume of distribution (V'd[area]) of chloramphenicol decreased progressively with increasing age between day 1 and day 42, so that the mean value for 42-day-old foals (362 +/- 163 ml/kg) was less than a third the mean value for 1-day-old foals (1,101 +/- 284 ml/kg). The mean value for V'd(area) in 1-day-old foals was significantly greater than values for: 7-day-old (491 +/- 158 ml/kg; P < 0.01); 14-day-old (426 +/- 65 ml/kg; P < 0.005); and 42-day-old (362 +/- 162; P < 0.0005) foals, and the mean value for V'd(area) on day 3 was significantly (P < 0.05) greater than the mean value for V'd(area) on days 7, 14, and 42. Using dosage calculations based on mean values for the pharmacokinetic terms derived for each age group, it was predicted that to maintain plasma chloramphenicol concentration > 8 microgram/ml, chloramphenicol sodium succinate (25 mg/kg) would have to be administered at dose intervals of 10, 3, 1.5, 1.5, and 1 hours in clinically normal foals 1 day and 3, 7, 14, and 42 days, of age, respectively. It was concluded that the marked changes in the disposition of chloramphenicol detectable during the first few days of life, the variation between individuals, the potentially major effect of prematurity, and the potential for compromised liver function in septicemic foals indicate that use of drugs, such as chloramphenicol, which rely heavily on hepatic metabolic processes for elimination, should be avoided whenever possible during the early neonatal period, unless plasma concentration is monitored.

The growth hormone (GH) secretagogue activity of variable dosages of clonidine (16.5, 50, 150, and 450 microgram/kg of body weight), given orally mixed with the daily food ration, was evaluated in young and old dogs. Significant (P < 0.05) increase in plasma GH concentration was detected at all dosages tested in young dogs and in response to all but the lowest dose tested in the old dogs fed the clonidine-containing diet. Old dogs had plasma GH concentration that exceeded that of young dogs when higher doses of clonidine were used. A clonidine (100 microgram/kg)-supplemented diet was fed to middle-aged dogs twice daily for 30 days. Significant (P < 0.01) increase of plasma GH concentration was observed on the first day of the feeding trial, but was undetectable by day 30. After feeding the clonidine-enhanced diet for 30 days, the effects on thymic morphology were variable, and there was no effect on plasma thymulin titer. Clonidine-fed dogs had significantly increased lymphocyte blastogenic responsiveness to mitogens, compared with that of control dogs, when evaluated as stimulation index.

A case-control study was done to identify factors associated with the development of equine degenerative myeloencephalopathy (EDM). Questionnaires were mailed to the owners of 146 horses admitted to the New York State College of Veterinary Medicine between November 1978 and June 1987 and diagnosed as having EDM by histologic examination. Questionnaires also were sent to owners of 402 clinically normal horses admitted to the college during the same period. Data were compared between the EDM-affected and control groups (56 and 179 questionnaires returned, respectively). Risk factors identified included the use of insecticide applied to foals, exposure of foals to wood preservatives, and foals frequently spending time on dirt lots while outside. Foals spending time outside on green pastures was a protective factor. Foals from dams that had had an EDM-affected foal were at higher risk of developing EDM than were foals from other dams.

Hematologic and serum biochemical values were determined in blood samples from 217 donkeys (Equus asinus). Donkeys were classified on the basis of size, sex, age, and whether they were domestic or feral. Parametric (mean +/- 2 SD) and nonparametric (2.5th to 97.5th percentile) reference ranges were calculated for each analyte. For all donkeys, 26 of 46 analytes significantly departed from gaussian distribution. Serum lactate dehydrogenase activity in miniature donkeys was higher than that in other donkeys. Differential leukocyte counts in feral donkeys differed from those in other types in ways that suggested that the former had smaller parasite loads or experienced greater stress. Erythrocyte, lymphocyte, and platelet counts and fibrinogen, glucose, inorganic phosphorus, and potassium concentrations decreased with age. Eosinophil counts, mean corpuscular volume, and plasma protein, serum protein, and serum globulin concentrations increased with age. Female donkeys had significantly (P < 0.05) higher mean corpuscular hemoglobin concentration and leukocyte and neutrophil counts than did male donkeys. Mean corpuscular hemoglobin increased with age, and females had higher values than did males of all age groups. An interaction between age and sex was observed for alkaline phosphatase activity, with a trend for decreased activity with age.