Epidemiological observations and heterosis analysis of gastrointestinal nematode parasitism in Suffolk, Gulf Coast Native, and crossbred lambs

A crossbreeding program was conducted to evaluate the resistant status to gastrointestinal nematode parasite infection in crossbred (F-1) lambs and their Suffolk and Gulf Coast Native (Native) breed counterparts. A total of 253 lambs were included in the study over 2 years. Fecal egg count (FEC) and blood packed cell volume (PCV) of 18-20 monitor lambs of each breed group in each year were collected every other week from birth to 24-30 weeks of age. The FEC and PCV of all lambs were determined at weaning (11-12 weeks of age) and at three subsequent times when anthelmintic treatment was administered. Nematode counts of wether lambs were obtained at 30 weeks of age in the first year. The epidemiological patterns of FEC and PCV of each breed group were similar in both years. The Suffolk group consistently showed the highest FEC and the lowest PCV, Conversely, the Native group had the lowest FEC and highest PCV, For the most part, all parameters for the Fl group fell intermediate to the Native and Suffolk groups. Nematode count followed the same pattern. Heterosis analysis showed that FEC, PCV, nematode count and weight gain of the Fl group favored the Native group. These results suggested that crossbreeding Suffolk to Native sheep may be a suitable way to produce lambs with improved resistance to gastrointestinal nematode infection, but production may be compromised. (C) 2001 Elsevier Science B,V. All rights reserved.