Thymic hyperplasia causing right ventricular outflow tract compression following treatment for oesophageal rupture in an Arabian colt

True thymic hyperplasia has been reported sporadically in the human literature as an immunological rebound phenomenon following immunosuppressive treatment or disease. There are limited accounts in domestic species, mainly following vaccination, and thymic hyperplasia has not been a recognised condition in the horse to date. This report details a case of true thymic hyperplasia in a 10-week-old Arabian colt diagnosed by histopathology of core biopsy samples. The colt developed pulmonary stenosis caused by compression due to a space occupying lesion in the cranial mediastinum following a 3-month history of hospitalisation for treatment of traumatic oesophageal rupture with perioesophageal abscess formation. Diagnostic imaging of the cranial mediastinum was indicative of a thymic mass, and histopathology confirmed the mass was normal (hyperplastic) thymic tissue. The colt was treated with a tapering dose of corticosteroids, which led to involution of the hyperplastic tissue and resolution of pulmonary artery compression. Thymic hyperplasia may be an unrecognised sequela to chronic inflammation in horses and was only identified in this case when the size was sufficient to compress right cardiac outflow.     

Development of the B- and T-cell compartments in porcine lymphoid organs from birth to adult life: an immunohistological approach.

Using immunohistological techniques, we studied the development over time of B- and T-cell compartments in the lymphoid organs of specific-pathogen-free pigs. Tissue samples were collected at various time-points, starting 2 days before the pigs were born until the pigs were 10 months old. The samples were collected from the spleen, thymus, peripheral lymph node, mesenteric lymph node, duodenum, jejunum, ileum, jejunal Peyer's patch and ileal Peyer's patch. Monoclonal antibodies specific to B- and T-cells were used to identify where the following cells were localized: IgM-B cells (cells positive to surface immunoglobulin), IgM-, IgG- and IgA-containing cells (cells positive to cytoplasmic immunoglobulin), and CD2-, CD4- and CD8-positive cells. The development of the B- and T-cell subpopulations in each organ was analysed. Two days before birth, most organs contained quantities of IgM-B cells. The spleen, lymph nodes, Peyer's patches and, notably, the thymus, contained some immunoglobulin-containing cells (Ig-CC); this finding indicates that pigs have cells that secrete immunoglobulins before birth. Just after birth, the incidence of Ig-CC increased in most organs; first IgM-CC increased, then either IgG- or IgA-CC increased, depending on the organ. T-cell development was observed clearly in spleen and in the lamina propria of the small intestine, in contrast to other organs, in which the T-cell compartments containing various T-cell subpopulations were well developed before birth. Comparison of the incidence of CD4+ and CD8+ cells showed that the CD4:CD8 ratio of these cells in the spleen, lymph nodes, Peyer's patches and small intestine is low, especially in adult pigs, compared with the CD4:CD8 ratio in other species. Weaning had little influence on the incidence of B- and T-cells in lymphoid organs. This study is the first immunohistological survey to describe the development of the major B- and T-cell subpopulations in various lymphoid organs of pigs, and it should be useful for future immunopathological and comparative immunological studies in pigs.     

Responses of calves to treadmill exercise during beta-adrenergic agonist administration.

Calves perorally administered the beta-adrenergic agonist (beta-A) clenbuterol for 28 d were studied before, during, and after a 12-min treadmill exercise. During exercise on d 1 of clenbuterol administration, respiratory rate, respiratory minute volume, and heart rate and blood glucose, lactate, and insulin concentrations increased more in beta-A-treated calves than in controls. Oxygen extraction rate and growth hormone concentrations were lower in clenbuterol-treated calves, whereas oxygen consumption, carbon dioxide production, and blood cortisol concentration increased similarly in the absence and presence of the beta-A. After 2 wk of daily clenbuterol administration, respiratory rate and respiratory minute volume during exercise were still higher and oxygen extraction was still lower, whereas all other measures were similar to those in controls. The increased heart rate in response to isoproterenol after 3 wk of clenbuterol administration was reduced markedly in resting but only slightly in exercising animals, whereas heart rate reduction by propranolol during exercise was similar to that in controls. Seven days after withdrawal of clenbuterol, newly administered clenbuterol evoked the same effects as on d 1. In conclusion, there were marked reactions to the first clenbuterol treatment that were in part enhanced during treadmill exercise. After 2 wk of beta-A administration, animals responded much less to the beta-A and changes were not different from those in controls. Resensitization to the beta-A was observed 7 d after its withdrawal.     

Effects of phenothiazine and thiabendazole on bovine dorsal pedal vein contractility induced by ergonovine and serotonin; Potential for alleviation of fescue toxicity

Phenothiazine and thiabendazole were studied for their ability to antagonize venoconstriction induced by ergonovine, and the biogenic amine serotonin, in the isolated dorsal pedal vein of cattle. The two compounds are commercially available, approved for usage in cattle and have been reported to reverse some of the toxic effects associated with the intake of Acremonium coenophialum-infested fescue forage by cattle. Neither compound had any antagonistic activity against venoconstriction induced by ergonovine. However, thiabendazole did have some activity against venoconstriction induced by serotonin. Ergot alkaloids are known to cause venoconstriction through effects on biogenic amine receptors, including serotonergic receptors, and since thiabendazole has anti-serotonin activity, part of the reported beneficial effects of thiabendazole in alleviating fescue toxicity may be due to the anti-serotonin activity of the drug. Further work is needed to determine if phenothiazine and thiabendazole have any effect on other types of alkaloids that are present in A. coenophialum-infested fescue.     

Reactivity of lichen lectins with blood typed canine erythrocytes

Extracts from 69 species of lichens were tested for their ability to agglutinate untreated and enzyme-modified erythrocytes from a panel of blood typed dogs. Forty-three lichen species reacted positively with either untreated or enzyme-modified cells. Many extracts exhibited differential agglutination among red cells tested. The patterns of differential agglutination observed with the lichen extracts did not correspond to known canine blood groups present on the test red cell panel.     

Causes of mortality and parasites and incidental lesions in dolphins and whales from British waters.

Detailed post mortem examinations were carried out on 18 dolphins and whales found dead on the coast of the United Kingdom. The commonest causes of death were pneumonia and entanglement in fishing gear. Of the non-fatal conditions, parasitoses of various organs were common and there was a wide variety of other conditions. In total 124 diseases and other lesions were found, giving an average of 6.9 conditions per animal.     

Bovine spongiform encephalopathy: aspects of the clinical picture and analyses of possible changes 1986-1990.

A standard questionnaire was used to record the presence of specific clinical signs reported for histopathologically confirmed cases of bovine spongiform encephalopathy observed before June 30, 1990, and the frequencies of these signs were analysed. The signs most frequently recorded were apprehension, hyperaesthesia and ataxia, and there were variations in the frequency with which some signs were recorded in animals observed at different times during the epidemic. These variations were considered to be the result of differences between observers and differences in the duration of the illness, rather than a change in the clinical picture, which could possibly have occurred with a change in the nature of the agent to which the cattle had been exposed, or to a change in their response to the agent.     

The effect of ticlopidine on canine platelets, fibrinogen, and antithrombin III activity

The effect of ticlopidine on platelet function, platelet number, mean platelet volume, antithrombin III activity, and fibrinogen was evaluated in 10 laboratory beagles. Ticlopidine (62 mg/kg) significantly inhibited ADP- and collagen-induced platelet aggregation within 2 days of the beginning of oral administration. Collagen-induced platelet 14C-serotonin release was not inhibited by day 9 of medication but was inhibited by day 20 in two of three beagles given medication for 32 days. Significant increases in mean platelet number were observed on days 2 and 5. The trend toward increased platelet number continued until day 16, at which time platelet number began to decrease toward baseline in three of three dogs treated for 32 days. Mean platelet volume (MPV) was significantly decreased compared to baseline on days 5 and 9. In three dogs treated for 32 days, the lowest MPV was observed on day 9 in two dogs and on day 12 in one dog. Significant changes were not observed in antithrombin III activity or fibrinogen with ticlopidine treatment.     

Thromboxane and prostacyclin production in ponies with colonic volvulus.

Effects of 1 hour of colonic volvulus and 3 hours of reperfusion on concentrations of thromboxane (TXB2) and prostacyclin (6-keto-PGF1 alpha) in portal, pulmonary arterial, and jugular blood were determined by radioimmunoassay to assess the site of production and clearance of these eicosanoids from the circulation in 5 anesthetized ponies. Colonic volvulus had no significant effect on mean arterial pressure or TXB2 concentrations, but significantly (P less than 0.05) increased 6-keto-PGF1 alpha concentrations in all blood samples. Immediately after colonic reperfusion, all eicosanoid concentrations were significantly (P less than 0.05) increased. Then, TXB2 returned to baseline values, whereas 6-keto-PGF1 alpha concentrations remained significantly (P less than 0.05) high for the remainder of the study. Eicosanoid concentrations were significantly (P less than 0.05) greater in portal blood than in pulmonary arterial and jugular blood samples at all periods. This suggests that the splanchnic circulation is the primary site of eicosanoid production during and after colonic volvulus and the liver appears to provide most of the circulatory clearance of thromboxane and prostacyclin.     

Methodology for assessing zinc bioavailability: efficacy estimates for zinc-methionine, zinc sulfate, and zinc oxide.

The bioavailability of zinc-methionine (ZnMET) was compared to that of feed-grade ZnSO4.H2O using three different diets: purified (crystalline amino acid [AA]), semipurified (soy isolate), and complex (corn-soybean [C-SBM]) diet. With the Zn-deficient purified or semipurified diet, weight gain and tibia Zn responded linearly to both ZnSO4.H2O and ZnMET supplementation. Common-intercept, multiple linear regression indicated differences in Zn bioavailability between ZnMET and ZnSO4.H2O for both diets as indicated by bone Zn. With the ZnSO4.H2O standard set at 100%, bioavailability of Zn from ZnMET was 117% (P less than .05) in the AA diet and 177% (P less than .01) in the soy isolate diet. The ZnMET was also compared to ZnSO4.H2O in a C-SBM diet containing 117 mg of Zn/kg. When high levels of Zn were added to this diet (0, 250, 500, and 750 mg/kg of supplemental Zn), consistent tissue Zn responses did not occur beyond the first increment. Addition of lower levels of supplemental Zn (0, 5, 10, 20, 30, 40 and 50 mg/kg) to a Zn-unsupplemented C-SBM basal diet (45 mg/kg of Zn), however, resulted in a broken-line, two-slope response in tibia Zn for both ZnMET and ZnSO4.H2O. Inflection points occurred at 60 and 54 mg of Zn/kg of diet for ZnSO4.H2O and ZnMET, respectively. The ratio of slopes (ZnMET:ZnSO4.H2O) below the inflection points was 206% (P less than .01), indicating that Zn was considerably more bioavailable in ZnMET than in ZnSO4.H2O for chicks consuming C-SBM diets. When feed-grade ZnO was compared to feed-grade ZnSO4.H2O in chicks consuming C-SBM diets, bone Zn slopes below the respective inflection points indicated that Zn was 61% bioavailable in ZnO relative to ZnSO4.H2O.