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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.

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Understanding the immunological basis of resistance to gastrointestinal nematode infections in livestock is important in order to develop novel methods of parasite control such as vaccination or genetic selection for parasite resistance. The present study aimed to investigate differences in immune response between parasite resistant Santa Ines and susceptible Ile de France sheep breeds to natural Haemonchus contortus infection. Parasitological parameters, humoral immunity, local and circulating cellular immune responses were evaluated in 19 Santa Ines and 19 Ile de France lambs undergoing different anthelmintic treatments regimens: suppressive treatments (SUP) or targeted selective treatments (TST) over a 5-month grazing period. Santa Ines lambs had significantly lower Haemonchus faecal egg count and worm burden compared to Ile de France regardless of treatment regime. In addition, circulating blood eosinophils count and parasite-specific IgG levels were significantly higher and more rapidly induced in Santa Ines lambs. Abomasal immune responses were generally greater in the resistant breed, which had significantly higher levels of parasite-specific IgA in mucus, and elevated number of globule leukocytes and CD3+ T cells within the abomasal mucosal. Furthermore, numbers of POU2F3+ epithelial cells, a tuft-cell specific transcription factor, were also elevated in the Santa Ines breed, suggesting that this breed is better able to initiate T-helper type 2 immune responses within the abomasum. In conclusion, the differential immunological responses detailed here are relevant to understanding resistance to gastrointestinal nematodes in other host breeds, as well as to resistance breeding as a sustainable control approach for parasitic infections.

This study aimed to evaluate the effects of supplementation with sunflower seeds and vitamin E for fattening lambs, on the chemical composition, cholesterol, vitamin E level, fatty acid profile and lipid oxidation of meat from sheep. Four treatments were evaluated, as follows: SC – basal diet consisting of sugarcane + concentrate; SCS – basal diet supplemented with sunflower seed; SCE – basal diet supplemented with 1000 mg vitamin E; SCSE – basal diet supplemented with sunflower seed and 1000 mg vitamin E. The Longissimus lumborum muscle of 32 Ile de France lambs, which were slaughtered when their bodyweight reached 32 kg, was used. The chemical composition of the lamb meat was not significantly different (P > 0.05) between the treatments. Sunflower seed supplementation increased (P < 0.05) the levels of linoleic acid, vaccenic acid and conjugated linoleic acid. Inclusion of vitamin E in the diet increased (P < 0.05) the concentration of vitamin E in the meat while decreasing lipid oxidation. Considering the current demand for healthy foods, inclusion of sunflower seeds and vitamin E in the diet of sheep is a viable possibility.

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Lamb performance was evaluated in four integrated crop-livestock (ICL) systems. The ICL areas were previously planted with maize and marandu palisade grass in December 2013. ICL systems 1 and 2 were also seeded with pigeon pea. After harvesting in April 2014, black oats were sown in rows (ICL 1 and 3) or by broadcast seeding (ICL 2 and 4). Each ICL area was divided into 12 paddocks of 225 m 2 to be grazed by young sheep from July 23 to September 30, 2014. To determine if the pasture remained contaminated by free-living stages of sheep gastrointestinal nematodes (GIN) after approximately ten months without animals in the area, 12 worm-free "tracer" lambs (n = 3/ ICL system) grazed each ICL pasture for 14 consecutive days in July 2015 and were later housed in pens, where they remained for another 14 days. The tracer lambs acquired no worm infections, demonstrating that the area was cleared after 300 days without animals. To evaluate GIN infection and uncastrated male lamb performance, we used 60 (n = 15/ system) Poll Dorset x Corriedale (crossbred) sheep with mean body weights of 24.4 ± 3.4 kg from July to September 2015 and 48 (n = 12/ system) Texel x Corriedale sheep with body weights of 26.4 ± 3.5 kg from June to September 2016. Lambs were allocated to the following groups: Group 1 rotated on the 12 ICL1 paddocks; Group 2 rotated on the 12 ICL2 paddocks; Group 3 rotated on the 12 ICL3 paddocks; and Group 4 rotated on the 12 ICL4 paddocks. Each paddock was grazed by sheep twice for three days, with a 33-day interval between grazing. At the end of the day the lambs were supplemented with concentrate plus silage. Groups 1 and 2 received mixed silage made of maize, marandu palisade grass and pigeon pea and groups 3 and 4 received mixed silage made of maize and marandu palisade grass. Faecal and blood samples were taken from all the animals every two weeks, and body weight was recorded on the same occasion. Nematode faecal egg counts (FEC), packed cell volume and total plasma protein means did not differ (P > 0.05) between the four lamb groups. In 2015, throughout the experimental period, the FEC decreased in all animals, with 6733 and 1407 eggs per gram (EPG) on average at the beginning and end of the trial, respectively. At the beginning of the trial in 2016, the animals had mild GIN infections (1077 EPG on average), and the individual faecal egg counts did not exceed 10,000 EPG during the trial. In decreasing order, Haemonchus spp., Trichostrongylus spp. and Cooperia spp. third stage larvae were found in the faecal cultures in both years. The performance of lambs were similar in the four ICL systems (P > 0.05), in the first and second years, the daily weight gains were 0.192 ± 0.05 kg and 0.221 ± 0.06 kg, respectively. In conclusion, a period of withdrawal of contaminated sheep results in plots free of infective larvae. The use of clean pastures during the dry season, in the different ICL systems, associated with a good nutrition plan, resulted in progressively declining degrees of GIN infections and satisfactory ...

The aim of this study was to evaluate the effect of two nutritional statuses on the productive performance of Dorper lambs naturally infected with gastrointestinal nematodes. Thirty-two lambs, grazing together on the same pasture, were allocated into four experimental groups: (G1) infected-supplemented diet, (G2) control-supplemented diet, (G3) infected-basal diet, and (G4) control-basal diet. Control animals received suppressive treatment with monepantel every two weeks, while precautionary anthelmintic treatments were given to all lambs of the infected groups with packed cell volume (PCV) <23%. There was reduction in the PCV means of all groups, which was more pronounced in the infected lambs that also presented reduction in total plasma protein values in comparison with the controls. Weight gain was affected by diet and infection status (P < 0.05). Daily body weight gain was 0.170 kg in the G1, 0.205 kg in the G2, 0.085 kg in the G3, and 0.116 kg in the G4. The cold carcass weight was 4.1% and 13.7% higher in controls in comparison with infected lambs, respectively, in the supplemented and basal diets. The infected groups, despite receiving precautionary anthelmintic treatments to prevent deaths due to haemonchosis, presented reduction in the production parameters in comparison with the controls.