This study was carried out to verify the association between the performance and the parasitic load of 28 growing Nelore bulls (one year old) naturally infected with gastrointestinal nematodes. From November/1999 to June/2000, the animals were weighed fortnightly and in this period fecal and blood samples were collected for laboratory analyses. The data of the egg counts per gram of feces (EPG) fitted into a negative binomial distribution model, indicating that the nematodes exhibit aggregated distribution. There was no clear evidence of association between the weight gain and the EPG or between the EPG counts and the packed cell volume (PCV). Eight of the 10 correlation coefficients between weight gain and PCV were negative, but only two were significant (P<0.05). The estimates of repeatability of the EPG, LOG (EPG + 1) and PCV were of 0.26, 0.25 and 0.33, respectively. Cooperia punctata was the species more frequently found and in heavier load parasitizing the animals. Besides this species, the following nematodes were observed: Haemonchus placei, Haemonchus similis, Trichostrongylus axei, Bunostomum phlebotomum and Oesophagostomum radiatum. The parasitism by these gastrointestinal nematodes at such loads apparently did not interfere with the growth of young bulls of the Nelore breed.
Cattle; Cooperia; Haemonchus; weight gain; packed cell volume
