Seasonal Fluctuation in the Number of Eggs of Trichostrongylid Worms in the Faeces of Ewes

Abstract

An account recently appeared in this journal of some work carried out by Zawadowsky and Zvjaguintzev (I933) on the seasonal fluctuations in the number of eggs of Nematodirus helvetianus in the faeces of a llama. As the observations of these investigators compare very closely with some which have been made at this experimental station on the fluctuations in the numbers of eggs of trichostrongylid worms disseminated in the faeces of ewes, it seems to be worth while recording the data, which although of no great value in themselves, give confirmation to some of the observations of Zawadowsky and Zvjaguintzev but suggest an alternative interpretation of their results. The inquiry into the amount of infective material disseminated by the ewes throughout the year was originally undertaken in order to obtain some idea of the relative importance of adult sheep as a reservoir of infection for the lambs. Ewes almost invariably carry a few trichostrongylid worms and outbreaks of disease with heavy losses amongst the adult sheep are by no means unknown. The possibility of their playing a part of major importance in producing heavy infection in the lambs, therefore, appeared to be worth a little investigation. Twelve average ewes were chosen for this purpose from the experimental station flock and samples of their faeces collected on the same day of each of sixteen consecutive months. An average egg count was made by thoroughly mixing equal weights of faeces taken from each of the twelve samples and estimating the number of eggs per gram of the mixture by a standard dilution technique. The laboratory flock grazes along with the cattle on 30 acres of good grass land. During the two seasons in which these observations were made, the lambs were born in February and March and for those two months the ewes were kept in the buildings and received hay and a little concentrated food but no grass or green food of any kind. For the remainder of the year they received no concentrated food at all but subsisted entirely upon the grass from the 30 acres of pasture. The twelve ewes were infected with species of Trichostrongylus, Ostertagia, Haemonchus, Cooperia, and Bunostomum, and although the multiple infestation detracts in part from the value of the results obtained, the similarity in the fluctuations in the egg count with those