RESISTENCIA A PARÁSITOS GASTROINTESTINALES EN OVINOS FLORIDA, PELIBUEY Y SUS CRUZAS EN EL TRÓPICO MEXICANO RESISTANCE TO GASTROINTESTINAL PARASITES IN FLORIDA, PELIBUEY AND CROSSBRED SHEEP IN THE MEXICAN TROPICS

Gastrointestinal parasites cause considerable losses in sheep production, and Florida Native sheep show a certain resistance to these parasites. An experiment was conducted in Tepetates, Veracruz, in which 32 six-to-eight-month-old lambs (15 ewe lambs and 17 ram lambs) were utilized including 6 Florida Natives (F), 6 Pelibuey (P), 8 FxP, 6 PxF and 6 more as a control group, based on lambs of all of these genotypes. The lambs received two parasite infestations (Phase 1 and Phase 2) while grazing in a sward of Andropogon gayanus Kunth. The experiment lasted 16 weeks. After each infestation, the elimination of parasite eggs (PEF) in feces, level of hemoglobin (Hb) and body weight of the lamb were measured. A design with repeated measurements was utilized with phase of infestation (P), lamb genotype (G) and sex of lamb (S) as discrete variables, plus week of sampling as a time factor. The results indicated that P, S, the interaction PxS, week of sampling (WS) and the interaction WS x P affected (p<0.01) both PEF and Hb. Ram lambs in Phase 2 showed higher PEF levels than ewe lambs (3631 vs 45 eggs per gram of feces). The means for Hb in Phase 2 were higher in ewe lambs than in ram lambs (11.6 vs 9.0 g). Haemonchus contortus was the most important parasite, with 40 larvae kg-1 of green matter in Phase 1 and 20 larvae kg -1 in Phase 2. The body weight was affected by the sex of the lamb (p<0.01), the interaction sex x genotype (p<0.05), WS (p<0.01) and the interaction WS x P (p<0.05). There were genotype differences in body weight among ewe lambs, but not among ram lambs; F x P ewe lambs were the heaviest group (26.3 kg) and the control group the lightest (19.9 kg). Lambs lost body weight from Phase 1 to Phase 2. It was concluded that the use of Florida sheep, both in purebreeding as in crossbreeding with Pelibuey, did not introduce resistance to gastrointestinal parasites.