Association between the skin thickness trait and susceptibility to tick Rhipicephalus microplus in Nelore cattle

• Grant number: 12/07623-0
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: November 01, 2012
• End date: October 31, 2013
• Field of knowledge: Agronomical Sciences - Animal Husbandry - Genetics and Improvement of Domestic Animals
• Principal Investigator: Josineudson Augusto Ii de Vasconcelos Silva
• Grantee: Ana Carolina Verdugo
• Host Institution: Faculdade de Medicina Veterinária e Zootecnia (FMVZ). Universidade Estadual Paulista (UNESP). Campus de Botucatu. Botucatu , SP, Brazil

Abstract

Methods commonly used to control the tick species Rhipicephalus microplus are based on acaricides, which have high costs in addition to presenting risks to cattle and often ineffective in control. The importance of using alternative methods offer economical approach to reduce losses caused by ticks. However, in literature, studies on mechanisms of resistance to cattle ticks are old, outdated methodologies of analysis, justifying the need for current studies. The objective of this study is to quantify the degree of diversity of the skin thickness for resistance to the tick species Rhipicephalus microplus in Nelore cattle and providing for breeders and technicians the ability to use the trait skin thickness as selection criteria. The project will be conducted with the use of 100 Nelore males, with ages around 450 days, from two farms located in the state of Sao Paulo. Two groups of animals per farm will be artificially infested by ticks, each group consisted of 25 cattle present skin thickness with values below two standard deviations from the mean population and 25 with values above two standard deviations. Larvae of female ticks collected on participating properties will be transported to the laboratory of EMBRAPA in São Carlos, SP, hatching, oviposition and egg division into portions containing about one gram (20,000 eggs) will be placed in 20 ml syringes. The contents of the syringes will be applied in the lumbar region of the animals in four infestations at intervals of 14 days. Five counts of engorged females will be held on the left side of each animal in the period between 19 and 23 days after each infestation. At the time of last count of ticks, the skin thickness will be measured in the posterior region of the animals the scapula through the caliper. The statistical package SAS will be used in assembling the database and conducting statistical analysis. The data count ticks and percentage return will be analyzed as repeated measures models that included the effect of group with respect to the skin thickness, infestation, their interactions and residue. Comparisons between groups will be evaluated by Tukey-Kramer test. (AU)