The development of Anaplasma marginale was studied in Dermacentor andersoni nymphs after they had fed on a calf with ascending Anaplasma infection. Gut tissues were collected on day 4 of tick feeding, from newly replete (fed) nymphs and on postfeeding days (PFD) 5, 10, 15, 20, and were processed for light and electron microscopy to determine density of A marginale colonies. Homogenates of gut tissues were prepared from nymphs collected on the same days and inoculated into susceptible, splenectomized calves to test for infectivity. Anaplasma colonies were detected in gut cells on PFD 5, 10, 15, and 20. Although colony density appeared to be higher on PFD 10 and 15, differences were not significant. Nymphal type-1 colonies were detected in highest numbers on PFD 5 and 10, transitional colonies were seen in highest numbers at PFD 10 and 15, and nymphal type-2 colonies were observed only on PFD 20. Gut homogenates that were collected from ticks at 4 days of feeding, when newly replete, and on PFD 20 caused anaplasmosis when injected into susceptible calves, but homogenates made from ticks collected on PFD 5, 10, and 15 were not infective. The data indicate that of the colony types of A marginale that develop in replete nymphs, nymphal type-1 and transitional colonies may contain organisms that are not infective for cattle.

Brain stem auditory-evoked responses were recorded in 9 male and 11 female clinically normal mature dogs, weighing between 2 and 36 kg. Mean wave latency for the entire group of dogs, using 60-dB hearing level click stimuli at 11/s for waves I to VII was: 1.41, 2.21, 2.85, 3.31, 3.71, 5.12, and 6.46 ms, respectively. The mean interpeak latency for waves I and V (IPLIV) was 2.32 ms. Neither gender nor ear effect was detectable. Positive correlation was observed between cranium length, cranium width, nasion-external auditory meatus interval, and body weight for wave-V latency and IPLIV. Such correlation was not documented for wave I. The regression equations for their effects on IPLIV were: cranium length, y = 0.05x + 1.85; cranium width, y = 0.07x + 1.32; nasion-external auditory meatus interval, y = 0.05x + 1.79; and body weight, y =0.05x + 2.15. On the basis of any of the 3 variables of cranium size or body weight, the study population could be classified into groups of large and small dogs, with the large group having significantly (P < 0.05) longer latency for wave V and IPLIV. It is recommended that the effect of size variation in dogs on brain stem auditory-evoked responses should be compensated for by use of the regression equation based on cranium length.

Cartilage retention strengths of laryngoplasty prostheses were compared in larynges of 2-, 3-, and 4-year-old horses, using doubled polyester and expanded polytetrafluoroethylene prostheses. Bilateral laryngoplasties were performed on each of 15 (seven 2-year-old, two 3-year-old, and six 4-year-old) larynges, which were collected at an abbatoir. Prostheses were secured to a mechanical testing machine, and tension causing arytenoid cartilage abduction was applied, until total failure of the cartilage or prosthesis resulted. Tension caused cricoid cartilage failure in 1 specimen, and muscular process cartilage failure in the remainder. There was no significant effect of age, prosthetic material, or side of prosthesis placement on cartilage retention of the prostheses. Additionally, frequency of multiple load-displacement peaks, indicating partial muscular process failure, was not affected by age or prosthetic material variables.

A field strain (87-8363) of bovid herpesvirus-4 (BHV-4) isolated from an aborted bovine fetus was used to inoculate pregnant rabbits. Eleven rabbits in midgestation were alloted to 4 groups consisting of 3 infected groups and 1 control group. Rabbits were inoculated with BHV-4 or mock-infected cell culture preparations via IV, intravaginal, and intrauterine routes. Mild vulvovaginitis and endometritis were observed after intravaginal and IV inoculation of BHV-4, whereas intrauterine inoculation of BHV-4 resulted in abortion of hemorrhagic fetuses and nonsuppurative endometritis. Virus was successfully isolated from organ explants of fetal tissues. Rabbits seroconverted 1 week after infection as detected by results of an indirect immunofluorescence assay.

A study was designed to determine whether phenytoin (PHE) prevents the myocardial necrosis and subsequent fibrosis produced by isoproterenol (ISO). Seven groups of female rats of the Wistar strain were used. Rats in groups 1 and 5 served as controls. Rats in group 3 were injected SC with 85 mg of ISO/kg of body weight for 2 consecutive days. Rats in groups 2 and 6 received 100 mg of PHE/kg orally. Rats in groups 4 and 7 received both PHE and ISO. There were 6 to 9 rats/group. Effects of ISO and PHE were evaluated gravimetrically, histologically, and electrocardiographically. Heart weight/body weight ratios for each group receiving ISO, with or without PHE, were greater than for groups not receiving ISO (P < 0.05). Light microscopic examination of heart sections of rats given ISO alone or ISO + PHE revealed multiple and diffuse areas of fibrosis. Fibrosis in hearts from rats receiving PHE + ISO was less severe than that in hearts from rats receiving ISO alone, but the difference was not statistically significant. Electrocardiographic changes of statistical significance were not observed in rats receiving any compound (alone or in combination), when compared with the control groups of equal age.

Cardiopulmonary effects of IV administered butorphanol tartrate (BUT) were assessed in 7 yearling steers medicated with atropine and anesthetized with guaifenesin, thiamylal sodium, and isoflurane in O2 for surgical placement of duodenal cannulae. Heart rate, respiratory rate, arterial blood pressures, pHa, PaCO2, PaO2, arterial [HCO3-], esophageal temperature, and end-tidal isoflurane concentrations were measured before and after IV administration of BUT (10 mg). Mean respiratory rate increased significantly (P < 0.05) only at 45 and 60 minutes after BUT administration. Mean respiratory rate was 26 +/- 6.3 breaths/min before BUT administration and 46 +/- 12.1 breaths/min 60 minutes after BUT administration. Arterial blood pressures were increased significantly (P < 0.05) at all times, except 5 minutes after BUT administration. The mean value for mean arterial pressure was 76 +/- 9.6 mm of Hg before BUT injection and 117 +/- 12.6 mm of Hg 60 minutes after BUT injection. Mean values for pHa and arterial [HCO3-] were significantly (P < 0.05) higher at 60 minutes after BUT administration (baseline, pH = 7.25 +/- 0.04 and [HCO3-] = 29.9 +/- 3.5 mEq/L; 60 minutes after BUT, pH = 7.28 +/- 0.03 and [HCO3-] = 33.0 +/- 1.8 mEq/L). Although some statistically significant changes were recorded, IV administration of BUT to these steers did not have a marked effect on the cardiopulmonary variables measured.

The hepatobiliary dynamics of a 99mTc-labeled derivative of iminodiacetate were investigated in 29 healthy dogs. A 2-compartment model proved to be adequate to describe the hepatic time-activity curve. Model-derived variables for the hepatic accumulation and the biliary excretion and transport were used as a reference for evaluation of a number of commonly used measurements directly derived from hepatic and bilary time-activity curves (graphic variables). The difference between t50(ex) and t95(ex), representing the moments when 50 and 95%, respectively, of the maximal count rate during the hepatic excretory phase were measured, proved to be an adequate graphic variable to quantitate biliary excretion. The use of other graphic variables to quantitate hepatobiliary functions seemed unjustified.

Postnatal ossification of the atlas and axis was studied in Miniature Schnauzers by examining alizarin-stained bone clearings, cleaned dry bones, radiographs, histologic sections, and arterially perfused bone clearings. Sixty-two pups (1 day to 16 weeks old) and 4 adults were examined. In 1-day-old pups, the atlas consisted of 3 separate ossification centers: a left and right neural arch center and midventrally, the intercentrum 1, which formed the body of the atlas. The axis contained 4 separate ossification centers: a left and right neural arch center; centrum 2 in the main part of the axis body; and centrum 1, which formed the caudal part of the dens and the cranial part of the axis body. By 6 weeks of age, the epiphysis on the caudal end of the axis body had begun to ossify. At this time, the intercentrum 2, which developed as a cuboidal ossification center intercalated between centrum 1 and centrum 2 in the middle of the cranial half of the axis body, also began to ossify. The centrum of the proatlas, which formed the apex of the dens, was first seen ossified in a 9-week-old pup. These 10 ossification centers were seen as constant and separate elements. In all dogs, the dens developed from 2 separate ossification centers: the centrum of the proatlas formed the cranial one-quarter, and centrum 1 formed the caudal three-quarters. Dens dysplasia is unlikely to be a result of failure of development of one of the ossification centers for the dens. Seemingly, vascular-related ischemia may lead to postnatal resorption of at least the middle part of the dens and result in dens dysplasia, with subsequent atlantoaxial subluxation. This condition in dogs may be a suitable animal model for the study of the pathogenesis of odontoideum and related conditions in man.

Results of a prospective serologic and virologic study of ruminant livestock in Central America and the Caribbean islands revealed bluetongue virus (BTV) to be enzootic in the 9 countries participating in the study. Bluetongue virus serotypes 1, 3, 6, and 12 were isolated from sentinel animals. To the authors' knowledge, these are the first isolations of BTV from the region studied and the first isolations of these serotypes in the Western Hemisphere. Clinical disease attributable to BTV infection was not observed in sentinel animals. The incidence pattern, with respect to age and geographic location, was determined. The need to evaluate the epizootiologic features of arthropod-borne viruses (arboviruses) on a regional ecologic basis is stressed.

Six mature Holstein bulls were each given 10 mg of phenylbutazone (PBZ)/kg of body weight, PO. Of the 6 bulls, 3 were given 10 mg of PBZ/kg by rapid IV administration 4 weeks later. Plasma concentration-vs-time data were analyzed, using nonlinear regression modeling (sum of exponential functions). The harmonic mean of the biologic half-life of PBZ was 62.6 +/- 12.9 hours after oral administration and 61.6 +/- 7.2 hours after IV administration. The mean residence time was 94.61 +/- 8.44 hours and 90.49 +/- 8.93 hours for oral and IV administration, respectively. The mean total body clearance was 0.0015 +/- 0.0003 L/h/kg, with the mean apparent volume of distribution 0.134 +/- 0.021 L/kg. Mean bioavailability was 73 +/- 2% after oral administration. Phenylbutazone was adequately absorbed from the gastrointestinal tract in bulls. The apparent volume of distribution was small, indicating that PBZ distributed mainly into plasma and extracellular fluid. The total body clearance was also small, which accounted for the long half-life of PBZ in bulls.