PHYSIOLOGY OF THE RESPIRATORY SYSTEM, SIGNIFICANT SPECIES DIFFERENCES, MEASUREMENTS OF PULMONARY FUNCTION, NORMAL VALUES AND SIGNIFICANCE OF VARIATIONS FROM NORMAL

The respiratory system of animals can be divided for evaluation into pulmonary system and circulatory system. The pulmonary system is involved in external respiration whereas the circulatory system is involved in internal respiration. External respiration is the exchange of oxygen (O₂) and carbon dioxide (CO₂) between the environment and circulating blood by way of the lungs and internal respiration is the transport of O₂ and CO₂ between the lungs and the metabolic machinery of the body cells.     

Response of pigs to recent isolates of Coxsackievirus B5

Coxsackievirus B5 (CB5) was serially passaged five times in pigs in an attempt to establish clinical disease. No clinical signs were seen although some pigs had a transient rise in rectal temperature. Viremia was not detected although virus was isolated from nasal swabs and fecal samples. No CB5 specific fluorescence or virus was detected in any tissues of five passages by immunofluorescent test and tissue culture methods, respectively.

Brain lesions were noted in all passages; extensiveness of lesions increased slightly up to the third passage although no evidence of increasing viral replication was found. No increase in brain lesions was found in the fourth and fifth passages. The development and progress of brain lesions were similar to but less extensive than those caused by swine vesicular disease virus (SVDV) in most pigs examined. Contact pigs also showed more brain lesions than inoculated pigs. In some passages, microscopic changes also were found in the heart. All pigs exposed to CB5 had positive neutralizing antibody titres against CB5 and SVDV but became ill after challenge with SVDV. There was an anamnestic response to both viruses following challenge.     

Efficiency of feeding Duddingtonia flagrans chlamydospores to grazing ewes on reducing availability of parasitic nematode larvae on pasture

Gastrointestinal nematodes are of concern in sheep production because of production and economic losses. Control of these nematodes is primarily based on the use of anthelmintic treatment and pasture management. The almost exclusive use of anthelmintic treatment has resulted in development of anthelmintic resistance which has led to the need for other parasite control options to be explored. The blood sucking abomasal parasitic nematode Haemonchus contortus causes severe losses in small ruminant production in the warm, humid sub-tropic and tropics. This study evaluated the effectiveness of a nematode trapping fungus, Duddingtonia flagrans, in reducing availability of parasitic nematode larvae, specifically H. contortus, on pasture. Chlamydospores of D. flagrans were mixed with a supplement feed which was fed daily to a group of crossbred ewes for the duration of the summer grazing season. A control group was fed the same supplement feed without chlamydospores. A reduction in infective larval numbers was observed in fecal cultures of the fungus-fed group. Herbage samples from the pasture grazed by the fungus-fed group also showed a reduction in infective larvae. There were no significant (P > 0.05) differences in overall fecal egg count, packed cell volume or animal weight between fungus-fed and control groups. Tracer animals were placed on the study pastures at the end of the study to assess pasture infectivity. Although tracer animals were only two per group, those that grazed with the fungus-fed group had substantially reduced (96.8%) nematode burdens as compared to those from the control group pasture. Results demonstrated that the fungus did have activity against nematode larvae in the feces which reduced pasture infectivity and subsequently nematode burdens in tracer animals. This study showed that D. flagrans, fed daily to grazing ewes, was an effective biological control agent in reducing a predominantly H. contortus larval population on pasture.     

Infection of pigs by Aujeszky's disease virus via the breath of intranasally inoculated pigs

Aujeszky's disease is a worldwide problem in the pig industry. In this experiment, four pigs chosen to act as shedder pigs were intranasally infected with Aujeszky's disease virus. Next, on three consecutive days, eight recipient pigs were exposed to the breath of a pair of shedder pigs via a mask-to-mask module. Except for the virtual absence of CNS signs, shedder pigs expressed clinical signs that were similar to pigs infected naturally or experimentally. Only mild respiratory signs occurred in recipient pigs, but all were infected by aerosols of Aujeszky's disease virus as evidenced by seroconversion. The pig is a much more sensitive indicator of airborne virions than our aerosol collection methods. We conclude that the mild respiratory disease acquired by the aerogenous route in recipient pigs is an easily managed model for studying the transmission of airborne respiratory infections and the immune responses to this type of infection.     

Comparison of minirhizotron and soil core methods for quantifying root biomass in a temperate alley cropping system

A study was carried out in southern Indiana, USA with the objective of comparing soil core sampling and the minirhizotron technique in quantifying fine root biomass and root distribution patterns in an alley cropping system with black walnut (Juglans nigra L.), northern red oak (Quercus rubra L.) and maize (Zea mays L.). Spatial variation in tree rooting pattern was investigated prior to planting maize. Tree fine root biomass was quantified at distances of 0, 1.1, 2.3, 3.5, and 4.3 m where 0 m represents the tree row and 4.3 m represents the middle of the alley. Root samples were collected to a depth of 90 cm using a hydraulic auger. Maize rooting pattern was determined 65 days after planting to the same depth. Using plexiglass access tubes installed near the actual soil core locations and a minirhizotron camera root images were recorded on a VHS tape. These images were later analyzed using a raster based GIS software (ERDAS-IMAGINE). Regression analysis revealed significant relationships between root surface area measurements from minirhizotron observations and fine root biomass data from soil coring for all species. Predicted fine root biomass data were also in close agreement with actual fine root biomass for all species examined. Maize root biomass was slightly, but not significantly, underestimated by the minirhizotron technique in the top 30 cm soil layer. No significant underestimation or overestimation of root biomass in surface or deeper soil layers was observed for the tree species. The results indicate that minirhizotron can be used in quantifying fine root biomass if site and species specific predictive models can be developed. This revised version was published online in June 2006 with corrections to the Cover Date.