The objective of this study was to evaluate two different gastrointestinal nematode treatment regimens. Fecal egg counts (FECs), proportion of nematode genera, weight gain, body condition score and reproductive indices (estrous cyclicity, conception and pregnancy rates) were evaluated in yearling heifers after imposing two treatment regimens for gastrointestinal nematodes: T1 = 306 calves treated in May and November with 3.5 % doramectin (700 μg/kg) and August (Aug) with saline solution; and T2 = 307 calves treated in May with 3.5 % doramectin (700 μg/kg), in August with 1% moxidectin (200 μg/kg) and in November with 3.5 % doramectin (700 μg/kg). The animals were weighed, and feces were collected for conducting FECs and coproculture. There was imposing of three fixed-time artificial inseminations (TAIs), and estrous cyclic and pregnancy statuses were determined. Cooperia was the most frequent genus detected in both groups. Heifers of the T2, as compared to those in the T1 group, had fewer FECs in November (P ≤ 0.05) and greater weight gain and average daily weight gain (P ≤ 0.05) from August to November. There tended to be more heifers of the T2 than T1 group estrous cycling (P = 0.07) at the beginning of the breeding season as well as greater pregnancy rates (P = 0.03) and conception rates (P = 0.03) as a result of the second FTAI. The results indicate there is greater reproduction outcomes as a result of strategic control of gastrointestinal nematodes in yearling Nellore heifers using the T1 as compared with T2 treatment regimen.
Keywords: Beef cattle; Body condition score; Fixed-time artificial insemination; Helminth burden; Pregnancy rate.
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