Parasitism in Angus x Nellore heifers in a silvopastoral system.

The influence of shade in the silvopastoral system on the performance and degree of parasitism by endo- and ectoparasites in Angus x Nellore heifers was assessed. The experiment was conducted with 72 heifers, with an initial mean weight of 276 ± 5.67 kg and 9 months of age, in a total area of 25 ha, divided into 12 paddocks, with three treatments and four replicates. The experimental design was a randomized complete block design, to evaluate the conventional grazing system (CGS) without shade and silvopastoral systems with simple line (SPS1) or triple lines (SPS3) of eucalyptus. The evaluations were carried out every 28 days, from June 2017 to April 2018. During the trial, the number of eggs per gram of feces (EPG) presented a gradual increase in the three systems. Differences (P < 0.05) in the variables analyzed were recorded only in two occasions: the CGS group EPG mean ± standard error (1269 ± 105) was higher than the SPS1 group mean (402 ± 129 EPG) in March, and tick average of the CGS group (13 ± 2.7) was lower than the SPS3 (32 ± 5.3) in October. There were no significant differences (P ≥ 0.05) between groups in relation to horn fly counts, the numbers of infective nematode larvae on pasture, hematological variables, and weight gain. It was concluded that in comparison with the CGS system, the shading in the SPS1 and SPS3 systems did not have any major influence on the degree of parasitism or in the performance of the heifers.

Development of Haemonchus contortus resistance in sheep under suppressive or targeted selective treatment with monepantel.

This study examined the development of resistance to anthelmintics in Haemonchus contortus in lambs under suppressive or selective treatment regimens that included monepantel. Twenty Ile de France and 20 Santa Ines lambs were allocated to two anthelmintic treatment regimens, based on body weight and nematode faecal egg counts (FEC): targeted selective treatment (TST) or suppressive treatment, both with monepantel. Lambs of the TST group were treated individually when they presented with a packed cell volume (PCV) ≤20%. On 7 October 2016, the lambs were allocated to clean pastures, where they grazed in separated paddocks by group until late February 2017. The experimental area was contaminated with nematodes that were introduced with the experimental Ile de France and Santa Ines lambs, naturally infected with gastrointestinal nematodes. To maintain the grazing lambs in the suppressive treatment group and their pasture as free of worms as possible, these lambs were treated with anthelmintics before being allocated to their paddock and then were periodically treated with monepantel. However, the use of a suppressive treatment regimen that included monepantel over a period of 3 months resulted in the emergence of a population of resistant H. contortus. In the TST group, there was a rapid and progressive reduction in the efficacy of monepantel, which at the end of the experiment was only 76%. The Ile de France lambs were all treated one or more times during the experiment, whereas only two Santa Ines lambs in the TST required treatment. In conclusion, a population of H. contortus resistant to monepantel emerged quickly during the rainy season, even when sheep were submitted to selective treatment.

Efficiency of partial treatment of cattle infested with horn fly using 40% diazinon.

The aim of this investigation was to evaluate the efficiency of partial treatment of animals infested with horn flies. Forty-five Guzerat cows between 4 and 7 years of age were divided into three groups (15 cows per group). The treatments were as follows: in groups G33 and G100, 33.3 and 100% of the cows were treated with one insecticide-impregnated ear tag/animal (40% diazinon), respectively, while in the group GC, the cows were not treated (control). The flies on the cervico-dorsal-lumbar region of the cows, in all three groups, were counted every 14 days. The experiment lasted from September 2006 to September 2009. Over this period, six four-month ear tag treatments, with intervals of one to two months, were conducted on both treated groups. The animals of group G33 had a higher infection than those of group G100, and the number of flies ranged from 12 to 27 (group G33) and from 3 to 11 (group G100). However, groups G33 and G100 had lower infection levels than group GC, which presented from 45 to 87 flies. Partial treatment of cattle infested with horn flies using 40% diazinon insecticide is an efficient alternative for controlling this ectoparasite.