Clinical signs, laboratory changes and toxicokinetics of brodifacoum in the horse.

Six horses gavaged with a commercial brodifacoum (BDF)-containing bait (Talone) at a dosage of 0.125 mg of BDF/kg of body weight showed weight loss, severe hypocoagulability and hemogram alterations. Four of the horses became depressed and anorectic; one required vitamin K1 therapy. Increases in clotting times were observed at 24 h in the partial thromboplastin time (PTT) followed by the thrombotest (TBT) and one-stage prothrombin time (PT) at 48 h. Elevated mean PTT, PT and TBT were observed from days 4 to 8 (p less than 0.05) with levels returning to pretreatment levels by day 12. Maximum prolongation was a fourfold increase in PTT (day 4), a 2.5-fold increase in TBT (day 6) and a twofold increase in PT (day 6). Thrombin clotting times remained unchanged. In two horses prolongation in clotting time did not normalize until day 23. The mean hematocrit (0.38 +/- 0.01 L/L) was decreased (p less than 0.05) from day 8 (0.33 +/- 0.02 L/L) to day 14 (0.33 +/- 0.01 L/L). The hemoglobin concentration and erythrocyte numbers were decreased (p less than 0.05) from day 6 (20.1%, 17.6% respectively) to day 14 (22%, 20% respectively). Platelet counts decreased on day 6 (17.2%) to nine (14.6%). No other significant changes were observed in routine hematological and serum biochemical parameters. Peak plasma concentrations of BDF occurred 2 to 3 h after oral administration; two horses had detectable levels of BDF at nine days. Pharmacokinetic evaluation indicated that BDF has a half-life of 1.22 +/- 0.22 days, a body clearance of 1073.1 +/- 53.21 mL/kg/day, a volume of distribution of 1853.7 +/- 26.41 ng-day/mL and closely approximates a one-compartment model in the elimination phase.(ABSTRACT TRUNCATED AT 250 WORDS)     

Distribution and controls on gross N mineralization-immobilization-turnover in soil subjected to zero tillage

The aim of this investigation was to provide quantitative measures of gross nitrogen (N) mineralization‐immobilization‐turnover (MIT) in soil, and of the parameters controlling MIT. This is needed to predict adequately mineral N availability in agricultural land. Respiration, MIT, soil microbial biomass (SMB)‐C, soil organic matter (SOM)‐C and dissolved organic matter (DOM)‐C were determined in soil collected over three depths at three stages in a continuous crop rotation. MIT was strongly correlated to the size and activity of SMB‐C and the size of SOM‐C but was only marginally affected by the stage in the crop rotation. The strength of the correlation of mineralization, immobilization and respiration with SOM‐C increased when analysed by curvilinear regression compared with linear regression because SOM bioavailability varied with depth. It is argued that the limiting step in the decomposition was the breakdown of SOM into DOM. The major pathway for degradation of organic‐N in this soil system appeared to be the MIT route, while only a small amount of N was likely to be assimilated in the organic form (direct route). Our findings suggest that modellers of C and N turnover in zero tillage cropping systems need to incorporate a curvilinear relationship between SOM pool size and MIT into their computer model(s).     

HELICAL COMPUTED TOMOGRAPHIC PORTOGRAPHY IN TEN NORMAL DOGS AND TEN DOGS WITH A PORTOSYSTEMIC SHUNT

Contrast enhanced helical computed tomography (CT) of the liver and portal system is routinely performed in human patients. The purpose of this project is to develop a practical protocol for helical CT portography in the dog. Ten clinically normal dogs were initially evaluated to develop a protocol. Using this protocol, ten dogs with confirmed portosystemic shunts (PSS) were then evaluated. Each patient was anesthetized, and a test dose of sodium iothalamate (400 mg I/ml) at 0.55 ml/kg was injected. Serial images were acquired at the level of T12-13 or T13-L1. The time to maximum enhancement of the portal vein was determined. This time period was used as the period between the second injection (2.2 ml/kg) and the start of the helical examination of the cranial abdomen. Delay times for normal dogs ranged from 34.5 s-66.0 s (median: 43.5 s) or 1.41 s/kg-4.12 s/kg (median: 2.09 s/kg). For patients with a PSS, the delay times were 16.5-70.5 s (median: 34.5 s) or 1.47-19.17 s/kg (median: 3.39 s/kg). The aorta, caudal vena cava, portal vein, shunt vessels, and their respective branches were well visualized on the CT images. Clinical case results were surgically confirmed. The surgeons reported that the information gained from the CT portography resulted in a subjective decrease in surgical time and degree of dissection necessary compared with similar surgeries performed without angiographic information. We believe that helical CT portography in the dog will be a useful adjunct in the diagnosis of PSS. The use of helical CT portography may allow clinicians to give clients a more accurate prognosis prior to surgery and will allow patients with lesions that are not surgically correctable to avoid a costly and invasive procedure.     

Regulatory T cells in cattle and their potential role in bovine paratuberculosis

The intracellular bacterium Mycobacterium avium subspecies paratuberculosis (MAP) causes Johne's disease in wild and domestic ruminants. Johne's disease presents as a chronic enteritis with severe inflammation of intestinal tissues, characterized by widespread infiltration of macrophages, the target cell of MAP. Clinical signs of Johne's disease are typically accompanied by a loss of peripheral CD4+ T cell responses to MAP antigens and an increase in anti-MAP serum IgG levels. Recently, it was proposed that regulatory T cells might develop over the lengthy course of subclinical MAP infection. In the past five years, significant progress in defining bovine regulatory T cells has been made. These studies grew out of observations that IL-10 is produced by PBMCs in response to MAP antigen stimulation and that neutralization of this IL-10 could enhance IFN-γ production from MAP-antigen reactive effector T cells. Depletion studies revealed that MAP responsive cell populations producing IL-10 were largely CD4+ and CD25+, although monocytes have also been shown to produce IL-10 in response to MAP. In addition, evidence for a regulatory population of γδ T cells has also begun to accumulate. We summarize current thinking regarding regulatory T cells in MAP infection and provide data suggesting a potential link between regulatory T cells, bovine leukemia virus, and MAP.     

The isolation and characterization of Campylobacter jejuni bacteriophages from free range and indoor poultry

Six hundred and sixty one samples – primarily fresh chicken faeces – were processed to isolate wild type Campylobacter jejuni bacteriophages, via overlay agar methods using C. jejuni NCTC 12662. The aims of this study were to isolate and purify bacteriophages and then test for their ability to lyse field strains of C. jejuni in vitro. Of all samples processed, 130 were positive for bacteriophages. A distinct difference was observed between samples from different poultry enterprises. No bacteriophages could be isolated from indoor broilers. The majority of bacteriophages were isolated from free range poultry – both broilers and egg layers. Bacteriophages were purified and then selected for characterization based on their ability to produce clear lysis on plaque assay, as opposed to turbid plaques. Two hundred and forty one C. jejuni field isolates were tested for sensitivity to the bacteriophages. Lysis was graded subjectively and any minimal lysis was excluded. Using this system, 59.0% of the C. jejuni isolates showed significant sensitivity to at least one bacteriophage. The sensitivity to individual bacteriophages ranged from 10.0% to 32.5% of the C. jejuni isolates. Five bacteriophages were examined by electron microscopy and determined to belong to the Myoviridae family. The physical size, predicted genetic composition and genome size of the bacteriophages correlated well with other reported Campylobacter bacteriophages. The reasons for the observed difference between indoor broilers and free range poultry is unknown, but are postulated to be due to differences in the Campylobacter population in birds under different rearing conditions.     

Multifocal discrete osteolysis in a horse with silicate associated osteoporosis

Silicate associated osteoporosis (SAO) was diagnosed post-mortem in an adult horse with the shortest documented exposure to cytotoxic silicates of 2 years. The horse was evaluated for a 6-month history of progressive back tenderness and acute onset of lameness. The horse had a marked (4/5) (American Association of Equine Practitioners scale) left forelimb lameness, moderate (2/5) hindlimb ataxia and weakness, and cervical pain upon palpation. Physical examination did not reveal clinical skeletal deformities or respiratory compromise. Radiographs revealed widespread, discrete, sharply delineated, osteolytic lesions in the skull, vertebral column, ribs, scapulae and middle phalanx (P2) of the left forelimb and a diffuse bronchointerstitial lung pattern. The presumptive clinical diagnosis was widespread, metastatic osteolytic neoplasia. Due to the poor quality of life and grave prognosis, the horse was humanely euthanised. Post-mortem examination revealed pulmonary silicosis in the lungs and hilar lymph nodes and osteolytic lesions with numerous, large osteoclasts and disorganised bone remodelling both consistent with SAO. SAO should be included as a differential diagnosis for horses with widespread, multifocal, discrete osteolysis and history of exposure to endemic regions with possible cytotoxic silicate inhalation. Exposure time of 2 years is potentially sufficient to develop SAO.