The epidemiology of parasitic gastro-enteritis of cattle

Abstract

Observations on parasitic gastro-enteritis of cattle are recorded with particular reference to its epidemiology under conditions existing in Queensland. The most important species of nematodes associated with this disease are Haemonchus contortus, Bunostomum phlebotomum, Cooperia punctata, C. pectinata, and Bosicola radiatus. All of these are serious among dairy cattle, but only H. contortus, Bosicola radiatus, and rarely Bunostomum phlebotomum among beef cattle. Ostertagia ostertagi and Trichostrongylus urei are common, but occur in pathogenic numbers only occasionally. Strongyloides papillosus and Moniezia sp., probably M. benedeni, are also discussed. The incidence and prevalence of these parasites are recorded and also the age of the calf when infestation was first detected. Pathogenic infestations are for the most part confined to young cattle 3 to 24 months of age. In dairy cattle, the most susceptible age is from 4 to 12 months; in beef cattle, the majority of outbreaks occur a few months after weaning. Outbreaks are usually seen during the winter and early spring, although on occasion, losses may commence in the autumn and occur also in early summer. Seasonal fluctuations in the populations of these helminths were followed by means of regular faecal egg counts. It was usual for the egg count of each species to increase to a peak, then to decline fairly rapidly, and to remain on a low level during the remainder of the period the animals were under observation, i.e. up to 18 months of age. The ages at which these peaks occurred are recorded and their relationship to the season of birth of the host is discussed. The influence of temperature and rainfall on the prevalence of these helminths has been studied and some preliminary observations are recorded on the development and behaviour of their preparasitic stages in the dung pad. Evidence is brought forward to show that cattle develop a strong resistance to infestation during the first 18 months or so of life. In young animals this reaction depends on exposure to infestation and is somewhat specific in nature in so far as it may be manifested against one species, but populations of other species may continue to increase. Thus, most animals became resistant to infestation with Cooperia spp. at about five months of age, but not to H. contortus and the other species until several months later. This resistance is considered mainly responsible for the light infestations usual among adult cattle. It appears strongest against B. phlebotomum and weakest against H. contortus, which is the most common and prevalent species among adult animals. Outbreaks of parasitic gastro-enteritis are considered to occur under conditions of high larval prevalence and poor nutrition, when resistance against infestation fails to be effective.