Embrapa Pecuária Sudeste, Rodovia Washington Luiz, km 234, Caixa Postal 339, CEP 13560-970 São Carlos, SP, Brazil.
Vet Parasitol. 2013 Oct 18;197(1-2):168-75. doi: 10.1016/j.vetpar.2013.06.021. Epub 2013 Jul 4.
The resistance to infestations by ectoparasites and infections by gastrointestinal nematodes was studied in 45 animals (males and females) of two genetic groups: purebred Nelore (NI, n=28) and Three-Cross (1/2 Angus+1/4 Canchim+1/4 Nelore - TC, n=17). The animals were monitored for 24 months, during which they were left to graze in tropical pastures without receiving treatment for parasites. Each month the animals were examined for infestations by external parasites, to count the numbers of cattle ticks Rhipicephalus microplus with diameter greater than 4.5mm present on the left side, horn flies (Haematobia irritans) present in the lumbar region and botfly larvae (Dermatobia hominis) present on the entire body. The H. irritans counts were performed with the aid of digital photographs. At the time of examination, fecal samples were collected to count the eggs per gram (EPG) and to perform coprocultures, and peripheral blood samples were drawn to determine the packed cell volume (PCV) and to count the eosinophils. For statistical analysis, the count data were transformed into log₁₀ (n+1), where n is the number of parasites. For PCV, significant effects (P<0.05) were found for collection month (CO), genetic group (GG) and gender (SX), with means and respective standard errors of 41.5 ± 0.65% for the NI animals, 39.3 ± 0.83% for the TC, 41.5 ± 0.72% for the females and 39.3 ± 0.77% for the males. Regarding the eosinophil counts, only the effect of sex was significant (P<0.01), with means and respective standard errors of 926.0 ± 46.2/μL, for males and 1088.0 ± 43.8/μL of blood, for females. The NI animals presented lower mean counts for all the external parasites compared to the TC animals (P<0.01). For ticks, the transformed means followed by standard errors for the NI and TC animals were 0.06 ± 0.01 and 0.34 ± 0.02, while for horn flies these were 0.92 ± 0.05 and 1.36 ± 0.06 and for botfly larvae they were 0.05 ± 0.03 and 0.45 ± 0.05, respectively. The average EPG values were only influenced by CO (P<0.01). The coprocultures revealed the presence of the following endoparasites: Haemonchus spp., Cooperia spp., Oesophagostomum spp. and Trichostrongylus spp., the last in smaller proportion. There were no significant differences between the genetic groups for the endoparasite loads, except for Cooperia spp., which were present in greater number (P<0.05) in the NI group. The results obtained in this experiment confirm previous findings of greater susceptibility of the Nelore breed to Cooperia spp. and high resistance to ectoparasites.
本研究旨在调查两种遗传群体的 45 头（公母各半）动物对体外寄生虫侵袭和胃肠道线虫感染的抵抗力：纯种内罗尔牛（NI，n=28）和三杂交牛（1/2 安格斯牛+1/4 金马毛牛+1/4 内罗尔牛 - TC，n=17）。这些动物被监测了 24 个月，在此期间，它们在没有接受寄生虫治疗的情况下被留在热带牧场上自由放牧。每个月都会对动物进行外部寄生虫感染检查，以统计左侧直径大于 4.5mm 的牛蜱（Rhipicephalus microplus）、腰椎区的虻（Haematobia irritans）和全身的蝇蛆（Dermatobia hominis）的数量。虻的数量是通过数字照片来统计的。在检查时，收集粪便样本进行每克粪便虫卵数（EPG）计数和粪便培养，并抽取外周血样以测定红细胞压积（PCV）和嗜酸性粒细胞计数。为了进行统计分析，将计数数据转换为 log₁₀（n+1），其中 n 是寄生虫的数量。对于 PCV，发现收集月份（CO）、遗传群体（GG）和性别（SX）有显著影响（P<0.05），NI 动物的平均红细胞压积（PCV）为 41.5 ± 0.65%，TC 动物为 39.3 ± 0.83%，雌性动物为 41.5 ± 0.72%，雄性动物为 39.3 ± 0.77%。关于嗜酸性粒细胞计数，只有性别效应有显著差异（P<0.01），雄性动物的平均嗜酸性粒细胞计数为 926.0 ± 46.2/μL，雌性动物为 1088.0 ± 43.8/μL。与 TC 动物相比，NI 动物所有体外寄生虫的平均计数均较低（P<0.01）。对于蜱虫，NI 和 TC 动物的转换后平均值分别为 0.06 ± 0.01 和 0.34 ± 0.02，而虻的平均值分别为 0.92 ± 0.05 和 1.36 ± 0.06，蝇蛆的平均值分别为 0.05 ± 0.03 和 0.45 ± 0.05。平均 EPG 值仅受 CO 影响（P<0.01）。粪便培养发现存在以下内寄生虫：血矛线虫、类圆线虫、食道口线虫和毛圆线虫，后者的比例较小。遗传群体对内寄生虫负荷没有显著差异，除了类圆线虫，NI 组的数量更多（P<0.05）。本实验的结果证实了内罗尔牛品种对类圆线虫的易感性较高和对外寄生虫的高度抵抗力的先前发现。
