Relationship between the excretion of protostrongylid larvae in sheep in north-west Spain and climatic conditions.

The relationship between different climatic factors (temperature, relative humidity and rainfall) and the pattern of lungworm larval excretion was studied in sheep under a continuous grazing pattern in North-west Spain, where the climate is intermediate between sub-humid Mediterranean with an Atlantic tendency and European Atlantic. Over a period of one year, 44 animals were sampled once a month at random from a flock of 80 Galician breed sheep, all over 4 years old. Faeces were taken directly from the rectum and the number of first stage larvae per gram of faeces was determined for each animal, and the species of Protostrongylidae (Nematoda) identified. Larval excretion was irregular during the study. The prevalence and intensity of infection were greater in the colder months (40.9%; x = 12.3 +/- 40.4) and less in the warmer months (21.9%; mean = 0.7 +/- 2.7). The species of Protostrongylidae identified and prevalences (%) were Neostrongylus linearis (71.5), Muellerius capillaris (18.8) and Cystocaulus ocreatus (9.7). Between November and March, with low temperatures, the prevalence and intensity of parasitism with N. linearis and M. capillaris were greater than in the months with high temperatures (May to September). Multiple linear regression analysis showed statistical correlation between temperature, relative humidity and rainfall considered together and the number of N. linearis larvae per gram of faeces. Linear regression showed a correlation between the temperature and the percentage of sheep that passed M. capillaris. In general, the prevalence and intensity of infection of the sheep with N. linearis, M. capillaris and C. ocreatus larvae decrease when the temperature increases and increase when the relative humidity and rainfall increases.