Drug-metabolizing enzyme activities were measured in livers from calves fed commercial milk replacer (nonfunctioning rumen [veal]), and those fed milk replacer supplemented with whole grain and hay from the first week of age (functioning rumen [ruminating calves]). After birth, cytochrome P450 and its NADPH-dependent reductase activities remained unchanged in veal calves; in ruminating calves they increased almost 50%. Cytochrome P450-mediated reactions, such as aniline hydroxylase activity, tripled in ruminating calves, but remained unchanged in veal calves. In both groups of calves, coumarin hydroxylase and 7-ethoxycoumarin 0-deethylase activities increased after birth, but maturation rates and activity values in ruminating calves were considerably greater than those of veal calves. The aminopyrine N-demethylase activity for veal calves was equal to that of calves with functioning rumen. Uridine diphosphoglucuronic acid glucuronyl transferase and glutathione-S-transferase activities also were higher in calves with functioning rumen than in veal calves. This increased activity in calves with functioning rumen probably represents a response to environmental exposure to xenobiotics. Compared with rumen-functional calves, bob veal (0 to 3 weeks old) and fancy veal (15 to 19 weeks old) calves fed commercial milk replacer have a significantly (P = 0.05) diminished capacity for metabolizing drugs and other xenobiotics. From a regulatory perspective, the variance in drug-metabolizing enzyme activities within these different market classes of calves suggests that specific studies designed to determine drug residue-depletion times in veal calves may be needed.

Although it is known that the QT interval is dependent on the preceding RR interval, QT interval does not vary during respiratory sinus arrhythmia, despite a wide variation in heart rate. To assess the rate of change of the QT interval following an abrupt increase or decrease in heart rate, QT intervals were measured from ECG of healthy, anesthetized, thoracotomized dogs in which a junctional rhythm had been induced by destroying the sinoatrial node. Atria were paced at 800- or 600-millisecond cycle durations until a steady state was reached, and then the cycle duration was changed suddenly to a new cycle duration (600 or 800 milliseconds, respectively). The time and number of heart beats required until the QT interval achieved a value of 63% (1 time constant) of the new steady state were calculated. Time constants for change in QT interval vs the number of beats following the change were 2.8 (SD = 1.3 s) seconds when heart rate was accelerated and 4.7 (SD = 2.1 s) seconds when heart rate was slowed. Differences were not statistically significant. The time constants for change in QT interval duration vs duration after the sudden change in heart rate were 1.7 (SD = 0.8 s) seconds when heart rate was accelerated and 3.7 (SD = 1.7 s) seconds when heart rate was slowed. These time constants differed significantly (P < 0.01). Response of QT interval, therefore, depended on the number of heart beats following sudden change in heart rate, but not time, except as time determined the number of heart beats. The QT interval did not change until 3 to 5 beats after the heart rate was suddenly changed. This number of beats would be more than that which would occur in 1 respiratory cycle in dogs; therefore, QT interval memory would prohibit changes in QT intervals that occur during respiratory sinus arrhythmia.

Fiberoptic bronchoscopy was performed in pigs to assess bacterial contamination of bronchoalveolar lavage fluids (BALF) obtained by use of the method and to determine the aerobic bacterial species in bronchoalveolar airways of healthy pigs. Bacterial contamination of BALF caused by insertion of the bronchoscope was evaluated, using a chromogenic bacterial tracer strain, and was found to be 0.22% of total colony-forming units (CFU), with range between 0 and 1.6%. A total of 164 pulmonary-healthy pigs from 6 closed herds were selected. The BALF obtained from these pigs were examined bacteriologically. Bacteria could not be isolated from 10.4% of all BALF; 5.5% of the BALF samples yielded pure cultures; and 84.1% yielded mixed aerobic bacterial growth. In BALF from 29.2% of the pigs, less than or equal to 5 X 10(2) CFU of bacteria/ml were isolated. The total number of bacteria in BALF from 50% of the pigs varied between 5 X 10(2) and 10(3) CFU/ml; 10.4% of BALF samples contained between 10(3) CFU/ml and 5 X 103 CFU/ml. More than 1 bacterial species were isolated from a single lung lavage of 84.1% of the pigs. Up to 6 species were isolated from a single BALF sample. A total of 443 bacterial isolates were differentiated into 25 bacterial genera and species. Samples of BALF yielded staphylococci (67.6%: Staphylococcus hyicus from 13.4% of the samples and S aureus from 2.4%), alpha-hemolytic streptococci (49.4%), Escherichia coli (42.1%), non-hemolytic streptococci (26.2%), Klebsiella spp (18.3%), micrococci (12.8%), and Coryneformes (11.0%). Other bacterial species were found, but less frequently. In our study, BALF from all pigs yielded < 5 X 103 CFU/ ml. Thus, low numbers of bacteria known to be facultative pathogens were isolated from BALF without causing detectable pneumonia.

Poly(methacrylic acid) hydrogels were tested for oral delivery of a vaccine against Pasteurella haemolytica infection in cattle. Culture supernatants of P haemolytica, the most common bacterium associated with pneumonia in cattle, were used as the antigens in the vaccine. Hydrogels containing culture supernatants were administered orally to calves. Calves were then challenge-exposed with virulent P haemolytica. Calves were euthanatized 3 days after challenge exposure. The lungs of each calf were scored for severity and size of pneumonic lesions. Results indicated that vaccinated calves had smaller, less severe pneumonic lesions and lived longer than nonvaccinated calves. These results indicated that hydrogels can be used to deliver vaccines orally to calves to enhance resistance to pneumonia caused by P haemolytica.

Holding power was determined for various orthopedic screws in bones of calves. Holding power was defined as maximal tensile force required to remove a screw divided by thickness of bone engaged by the screw (kN/mm). Comparative pull-out tests were performed, using pairs of large metacarpal or metatarsal bones from calves aged 3 to 14 days. Comparisons were made of the holding power of 6.5-mm fully threaded cancellous screws and 5.5-mm cortical screws in the proximal and distal metaphyses, and of 4.5-mm and 5.5-mm cortical screws in the diaphysis. Sixteen repetitions of each comparative trial were performed. There was no statistically significant difference in the holding power of 4.5- and 5.5-mm cortical screws in the diaphysis. There was no significant difference in the holding power of 5.5-mm cortical and 6.5-mm fully threaded cancellous screws in the proximal metaphysis. In the distal metaphysis, 6.5-nu-n fully threaded cancellous screws had significantly (P < 0.001) greater holding power than did 5.5-mm cortical screws. There was no significant difference between the mean holding power of 5.5-mm cortical screws in the proximal metaphysis and 5.5-mm cortical screws in the distal metaphysis. There was significantly (P < 0.01) greater mean holding power of 6.5-mm cortical, fully threaded cancellous screws in the distal metaphysis, compared with the proximal metaphysis.

The hypothesis that equine laminitis is caused by thrombosis of vessels in the laminar corium (dermis) was investigated. Hemostatic alterations were evaluated by determining platelet count, platelet survival, platelet adhesiveness to vascular subendothelium, activated clotting time, and whole blood recalcification time. Thrombosis of vessels in the hoof wall was evaluated by scintigraphic studies of the hoof wall after administration of indium-111 ((111)In)- labeled platelets, contrast arteriography, and histologic examination. Platelet count remained constant before and at the onset of lameness; however, survival of (111)In-labeled platelets was shortened. Scintigraphy of affected feet revealed accumulation of (111)In-labeled platelets distal to the coronary band. Arteriography of disarticulated saline-perfused feet revealed marked reduction in blood supply to affected hooves. Histologic examination of the laminar dermis disclosed variable numbers of microthrombi in dermal veins of affected feet from 3 of 4 ponies with laminitis. Whole blood recalcification time was shortened at 8 hours after administration of carbohydrate and was prolonged at the onset of laminitis. Activated clotting time was prolonged at 32 hours after carbohydrate administration and at the onset of lameness. Plasma endotoxin-like activity was detected in 1 of 4 affected ponies. These data confirm that microvascular thrombosis existed at the onset of lameness in ponies with carbohydrate-induced laminitis and indicate that systemic coagulopathy may have preceded development of thrombosis.

A solid-phase ELISA to detect antibodies bound to the surface of canine platelets (platelet-bound antibodies) is described. Using this assay, the effect of anticoagulant and storage time of anticoagulant blood on the concentration of antibodies bound to the surface of platelets from clinically normal dogs was investigated. Blood from 3 clinically normal dogs was anticoagulated with acid citrate dextrose, Na3 citrate, and aqueous K3 EDTA and stored on ice for up to 48 hours. Platelet-bound antibody concentration was measured on platelets isolated from anticoagulated blood immediately after venipuncture and subsequent to storage of blood for 24 and 48 hours. Differences in platelet-bound antibody concentrations were investigated among dogs, anticoagulants, and storage times by ANOVA and Bonferroni pair-wise comparison of means. There was no effect of dog on platelet-bound antibody concentration. The effect of time was significant (P < 0.0001), with higher concentration of platelet-bound antibodies detected with increasing storage time. Effect of anticoagulant on platelet-bound antibody concentration was not statistically significant; however, there was a trend to increasing concentration of antibodies bound to platelets isolated from Na3 citrate- and K3 EDTA-anticoagulated blood. Moreover, there was significant (P = 0.02) interaction between anticoagulant and time. Platelet-bound antibody concentration increased with storage of anticoagulated blood prior to platelet isolation and with use of Na3 citrate and K3 EDTA anticoagulants. The preferred anticoagulant for platelet-bound antibody measurement is acid citrate dextrose. Platelet-bound antibody concentration should be determined not longer than 24 hours after blood collection.

The usefulness of tidal breathing flow-volume loops (TBFVL) to evaluate pulmonary function was investigated in 6 Standardbreds during treadmill exercise. Tidal breathing flow-volume loops are a graphic representation of airflow rate vs tidal volume for each individual breath. These TBFVL were obtained from horses exercising it speeds corresponding to 75 and 100% of maximum heart rate. Measurements were recorded in each horse before and after ovalbumininduced allergic lung disease. Moderate obstructive lung disease, characterized by a significant increase in pulmonary resistance, was observed while the horses were at rest. We found that in horses with airway obstruction exercising at 75 or 100% of maximum heart rate, the quantitative indices describing TBFVL shape and size were not markedly different from those in clinically normal horses exercising at similar speeds.

Efficacy of abamectin against gastrointestinal tract nematodes and lungworms of cattle was determined in 4 experiments. The first 2 experiments were controlled trials in which efficacy was determined at necropsy in calves with either experimentally induced (n = 14) or naturally acquired (n = 16) infections. Half the calves in each experiment were treated with abamectin (200 micrograms/kg of body weight, sc), and half were left untreated as controls. Efficacy was > 99% against adult stages of Dictyocaulus viviparus, Haemonchus placei, Ostertagia ostertagi, Trichostrongylus axei, Cooperia punctata, Trichuris discolor, and C oncophora, and was 92.4% against Nematodirus helvetianus. The second 2 experiments were clinical trials in which efficacy was determined by fecal egg count reduction in naturally infected yearling heifers (n = 75) or 2-year-old heifers (n = 75). Within replicates of 5, 4 heifers were assigned at random to treatment with 200 Kg of abamectin/kg and 1 was left untreated as a control. Abamectin was 100% effective in eliminating strongylate nematode eggs from the feces of these heifers. In all experiments, adverse reactions were limited to small, clinically unimportant injection site swellings in 29% of abamectin-treated calves. Abamectin was judged to be safe and effective in these trials.

The safety of moxidectin 1% injectable anthelmintic (0.6 mg/kg of body weight, 3 times the recommended dose) was evaluated in 145 reproductively sound, beef cows undergoing estrous cycle. Five treatment groups received moxidectin 1% injectable at specific times relative to a synchronized estrus (day 0): preovulatory treatment (day -2, treatment group 1), treatment at ovulation (day 0, group 2), and treatment after ovulation (days 7, 14, and 28, group 3, 4, and 5, respectively). Two groups of control cows received an injection of vehicle only at times corresponding to treatment in the other groups (6 at days -2, 7, and 28; 7 at days 0, 7, and 14). A final control group (8) received neither product or vehicle. Adverse clinical reactions were not observed in moxidectin- or vehicle-treated cows. Cows were bred by artificial insemination between days -2 and 25 and, subsequently, by breeding-sound bulls through day 65 of the study. Treatment and control groups did not differ in pregnancy rate or time to conception. Moxidectin (at 3 times the therapeutic dose) did not have deleterious effects on cow reproductive performance as examined (eg, at folliculogenesis, ovulation, and the early embryonic phase of development).