Seasonal Changes in the Structure of Nematode Populations of Cattle in New South Wales in Relation to Inhibited Larval Development

Abstract

Pasture plots in 3 climatic regions were contaminated with worm eggs of Ostertagia ostertagi, Trichostrongylus axel, Haemonchus spp and Cooperia spp in the autumn, winter and spring. Successive pairs of parasite‐free calves were grazed on the plots for 7 to 10 days at 4‐week intervals and then killed for worm counts 14 days after their removal from pasture. On the Northern Tablelands of New South Wales, irrespective of the season of pasture contamination, the degree of inhibition of O. ostertagi was low in winter and highest in spring. T. axei showed similar trends while Cooperia spp showed negligible inhibition. On the North Coast of New South Wales, inhibited larvae accounted for a very small proportion of the O. ostertagi burdens, while in comparison T. axei showed a much greater degree of inhibition. Larval inhibition of Haemonchus spp occurred in autumn and early winter after which it did not occur. There was negligible inhibition in Cooperia spp. On the Central Coast of New South Wales, there was little inhibition of O. ostertagi and none in T. axel. For Haemonchus spp, inhibited larvae were found mainly in autumn and winter. The numbers of inhibited Cooperia larvae were also highest in autumn and winter and were associated with large worm burdens. The marked difference between the tablelands and coastal regions in the seasonal trends of inhibition of O. ostertagi was considered to be due to a difference in strains between the geographical regions. The possible effect of climatic factors on the inhibition‐proneness of infective larvae on pasture is discussed for Ostertagia and other nematodes. The roles of host resistance and density‐dependence are also discussed.

Pattern of Occurrence of Gastrointestinal Strongylosis in an Organized Caprine Farm of Wayanad district, Kerala, South India

“…It is well documented that gastrointestinal parasitism in grazing animals is directly related to the availability of larvae on pasture and seasonal pasture contamination (Smeal et al, 1980). The warm and humid climate favours the development and survival of preparasitic stages (Durie, 1961).…”

Inhibited development of Ostertagia ostertagi in Australia related to survival over summer in the host or on pasture

“…The production and management of tracer calves has been described by Smeal & Donald (1981). Worms were recovered and counted by the technique of Smeal et al (1980). Total 0. ostertagi counts in these tracers were subjected to a split-plot-in-time analysis of variance with ' sources of contamination' and ' sampling times' as the main effects, after transformation of counts according to the expression y = log (a;+ 25).…”

“…In Australia,, inhibition in 0. ostertagi occurs in late winter and spring (Smeal, Hotson, Mylrae, Jackson, Campbell & Kirton, 1977), and varies in degree between different naturally occurring ecotypes of the parasite (Smeal, Fraser & Robinson, 1980). This variation is genetically determined with a greater frequency of inhibited forms in beef than in dairy cattle production systems (Smeal & Donald, 1981, 1982a.…”

Seasonal fluctuations and hypobiosis of gastro-intestinal nematodes of Awassi lambs in Iraq

“…This difference was attributed to the host immune response, especially in view of the lymphoid cell infiltration noticed in the mucosa of the previously infected calves. Smeal, Fraser & Robinson (1980) reported a marked difference in the degree of hypobiosis in O. ostertagi larvae populations in calves between a warm coastal region (New South Wales) and the cold Northern Tablelands of Australia. According to them, this could be due to a genetic difference between geographically isolated populations or to the direct effect of climatic differences on the free-living stages on the pastures.…”