Deposition and clearance of monodisperse aerosols in the calf lung: effects of particle size and a mucolytic agent (bromhexine)

Mucociliary clearance and retention of monodisperse aerosols of radiolabelled polystyrene particles of both 3.3 microns and 5 microns diameter were investigated in four healthy calves and two sick calves. The effect of the mucolytic agent bromhexine was also assessed at two dosage levels. There were significant differences (P less than 0.05) in clearance rate constant between calves, but similar patterns of clearance for each calf. These characteristics of mechanical lung clearance did not vary over a two month period. Values of clearance rate constant and percentage retention varied significantly (P less than 0.001) between the two different particle sizes, 5 microns particles giving faster clearance and lower retention of particles than 3.3 microns particles. Bromhexine at the recommended dose of 1.6 mg/kg 0.75 caused a significant (P less than 0.05) increase in clearance rate in both healthy and sick calves, but affected percentage retention only in sick calves. This study illustrates the variation in mucociliary clearance rates shown by individuals and also underlines the importance of particle size in aerosols used for studies of pulmonary deposition and clearance. The work also indicates that bromhexine may be of use in the therapy of respiratory disease in calves.     

Immunological and feeding studies on antigens derived from the biting fly, Stomoxys calcitrans.

Pairs of rabbits were immunised with three antigenic preparations derived from Stomoxys calcitrans gut, abdominal section and whole flies. Immunoblotting studies demonstrated that a humoral response was mounted against eight antigens from the gut preparation and 12 each from the abdominal and whole fly preparations. In vitro feeding experiments showed higher mortality between Days 4 and 7 in the group of flies which had fed upon blood from rabbits inoculated with the gut derived antigen. This group also produced the lowest percentage of viable eggs (15.5%).     

Host range of A/Chicken/Pennsylvania/83 (H5N2) influenza virus

The highly pathogenic A/Chicken/Penn./1370/83 (H5N2) avian influenza virus, which caused 80% mortality in chickens in Pennsylvania, produced only mild transient illness in experimentally infected pheasants, little or no clinical signs in ring-billed gulls and pigs, and no clinical signs in pekin ducks. Virus could be recovered from only the upper respiratory tract of gulls and pigs for 1-2 days. Infection in ducks resulted in intestinal replication of virus in only 1 out of 12 ducks. By contrast, pheasants shed virus in feces (10(4.7) EID50) for at least 15 days. These studies reinforce wildlife surveillance findings indicating that gulls and ducks are unlikely to have transmitted virus between chicken farms during the 1983 outbreak. Although experimental data suggest that wild gallinaceous birds such as pheasants are potentially capable of virus transmission, there has been no evidence of this from wildlife surveillance in Pennsylvania. Experimental infection of chickens with H5N2 virus isolated from wild ducks one year before the Pennsylvania outbreak or a gull virus (H5N1) isolated in the quarantine area in 1983 resulted in asymptomatic infections and virus replication occurring only in the upper respiratory tract. These studies suggest that if the first H5N2 virus infecting chickens in Pennsylvania originated from waterbirds, changes in host specificity and pathogenicity for chickens and other gallinaceous birds probably occurred during emergence of the Chicken/Penn./83 virus. It is recommended that attention be given in the future to the isolation of domestic poultry from contact with wild aquatic birds.     

Haematology of veal calves reared in different husbandry systems and the assessment of iron deficiency

Calves were reared for veal and fed milk replacer either alone or with straw or dry feed of varied iron content. Measurements of haematology and iron biochemistry were made at the start of the rearing period and before slaughter at 16 to 20 weeks of age. When the total dietary iron intake rose to approximately 12,500 mg (an average of 112 mg/dl, approximately 60 mg/kg dry matter) haemoglobin concentration reached a mean value (+/- sd) of 12.4 +/- 1.1 g/dl, similar to control calves. There was no further increase in haemoglobin when more iron was fed, indicating that there was sufficient iron in the diet for normal erythropoiesis. The borderline of iron deficiency anaemia at 16 to 20 weeks of age was defined as a haemoglobin concentration of 9 g/dl and a saturation of total iron binding capacity of 10 per cent. There was evidence of diurnal variation in serum iron concentration in calves fed in a periodic manner. The feeding of straw to veal calves did not prevent iron deficient erythropoiesis.     

Comparison of the time required to administer three different fluke and worm combination products to commercial beef cattle at housing

Larger livestock units, a decline in the farm labor force, animal welfare concerns, and a trend toward more selective use of drugs have increased the focus on animal handling, time management, convenience, and compliance in administering veterinary therapeutics. This study was undertaken to quantify and compare the time needed to treat commercial beef cattle with three fluke and worm combination products with different administration profiles. Young beef cattle (n = 270) weighing approximately 400 kg were allocated to batches of five, which were randomly assigned to receive ivermectin + clorsulon injection, ivermectin + closantel injection, or levamisole + triclabendazole oral drench. The mean time needed to administer ivermectin + clorsulon (single injection) to five cattle was 31 seconds, which was significantly less than the 100 seconds needed for ivermectin + closantel (two injections) and the 126 seconds needed for levamisole + triclabendazole (P less than .001). Such quantitative data can allow for better planning and selection of parasiticide treatment approaches at the farm level.