A study of pathogenic factors in experimental bovine oesophagostomosis. I. An assessment of the importance of anorexia

Abstract

Pathogenetic factors in bovine oesophagostomosis have been investigated by comparing, in calves of the same breed subject to equalized feeding in pairs, the state of health and thriftiness of infected and control groups. Infection was produced by the administration of 7000 Oesophngosfomum rutiintum larvae. The resulting disease varied from mild to moderately severe in its effects, and was of comparatively brief duration. First signs were seen at 3-5 weeks, improvement began at 10 weeks, and the animals were recovering well at 14 weeks. Infected calves developed an anorexia which was first made evident by a rapid reduction in the mean daily feed intake during the fourth week following infection, succeeded by a slow return to the pre-infection level of' intake about 14 weeks later. In control calves, the same reduction in food intake was imposed over the same period by withholding some of the ration. In control calves the only definite departure from normal was a reduction in the rate of gain in body weight that would be expected in similar calves fed ad libitum, and some retardation in growth. Infected calves on the same feed intake as control animals showed a much greater departure from normal in respect of rate of gain in weight, and their growth was more severely retarded. The mean feed utilization of these calves was 0.039 lb per pound of feed, as compared with 0.095 lb per pound of feed for the worm-free controls. Furthermore there was observed, only in the infected animals, diarrhoea, a normochromic normocytic anaemia, and a hypoproteinaemia. The most severe pathological changes in the hosts occurred when the helminths were in the early fifth stage of development. It is concluded that anorexia is a factor which, through reduction of food intake, contributed considerably to pathogenesis. Other factors together exercised an effect almost as great. These other factors have yet to be investigated and defined.