The Occurrence and Seasonal Magnitude of the Periparturient Rise in Trichostronglyid Nematode Egg Output in Breeding Yankasa Ewes in a Sub Humid Climate

Abstract

Investigations were carried out on the occurrence of a periparturient rise in Trichostrongyle egg counts in breeding ewes grazing natural pastures. The first study using ewes in the last month of gestation and non-pregnant ewes as controls, showed that a significantly (p<0.05) greater increase in egg counts (EPG) occurred in the lambing ewes when compared with the non-pregnant ewes. Peak EPG was 357.1±94 four weeks after lambing while it was 190±162 in non pregnant ewes. A second study using ewes grazing a separate pasture showed an exponential increase in mean EPG from 187±124 pre lambing to 1589±429 two weeks post lambing. A third study investigated the effects of season on the magnitude of the periparturient rise. Ewes whose lambings were timed to coincide with four seasons (late dry, early wet, late wet and late dry seasons) were monitored from 4 weeks pre to 5 weeks post lambing. The periparturient rise occurred irrespective of season of lambing but the magnitude was influenced by the season. The highest periparturient rise occurred in the late wet season (peak of 4201±1813) four weeks post lambing while the lowest occurred when lambing coincided with the late dry season (peak of 1800±765). Packed cell volume values in lambing ewes declined with increased egg counts but total protein values did not show appreciable changes. The periparturient rise in helminth egg counts is an important epizootiologic consideration in the study area and tactical treatment in its elimination will reduce infection for lambs, lower mortality and increase productivity of ewes.