Comparison of naturally acquired parasite burdens among Florida Native, Rambouillet and crossbreed ewes

The response to natural infection by gastrointestinal nematodes was evaluat ed in three groups of lambing mature ewes: 16 Florida Native; 21 Rambouille t; and 18 1/2 Florida Native x 1/2 Rambouillet (F1 generation). Fecal egg c ounts (FEC),packed cell volume (PCV) and plasma protein levels were determi ned periodically through a one-year period. The highest FEC was recorded in Rambouillet ewes, with most of the means higher than 1000 eggs per gram (E PG). Florida Native and Fl ewes showed similar trends in FEC, with most of the means below 500 EPG. The highest mean PCV values were recorded in Flori da Native ewes, followed in decreasing order by Fl and Rambouillet ewes. Fl ewes showed the lowest plasma protein levels and Florida Natives the highe st. Fecal cultures revealed the highest percentages of Haemonchus larvae in Rambouillet ewes (>64%) and the lowest percentages in Florida Native ewes. Florida Native and Fl ewes were more resistant to gastrointestinal nematod e infections than were Rambouillet ewes. High negative correlation coeffici ents between FEC x PCV and FEC x plasma protein levels coincided with peaks in mean FEC of Rambouillet (May and July), Florida Native and Fl ewes (Oct ober). This study showed that crossbreeding Rambouillet and Florida Native sheep resulted in the production of Fl ewes resistant against gastrointesti nal nematode infections. (C) 1999 Elsevier Science B.V. All rights reserved .