Bovine genetic resistance effects on biological traits of Rhipicephalus (Boophilus) microplus

Abstract

This study aimed to verify the influence of bovine genetic resistance on biological traits of the Rhipicephalus (Boophilus) microplus tick. Genetic resistance or susceptibility was determined according to breeding values for tick counts, predicted using a dataset of 9007 Hereford and Braford (Hereford×Zebu) bovines naturally infested and raised under extensive production systems in southern Brazil. From a total of 974 Braford heifers born in 2008, 20 were classified as genetically tick-resistant and 20 classified as genetically tick-susceptible, and used to obtain the ticks samples used in this study. The 40 heifers were exposed to four subsequent artificial infestations with approximately 20,000 larvae at 14-day intervals. From the 19th to 23rd day of each infestation tick counts were performed on the left body side of the heifers. Engorged ticks were manually collected on the day of highest observed burden after each infestation. Tick counts on susceptible heifers were 5.5, 10.5, 11.1 and 6.9 times larger than on resistant heifers, respectively, after the first, second, third and fourth artificial infestations. In the third infestation, ticks from resistant heifers showed lower egg production index (P<0.0001) than ticks from susceptible heifers. In the fourth infestation, ticks from susceptible group showed higher egg mass weight (P<0.05) and nutrient index (P<0.0001) than ticks from resistant heifers. Tick initial weights showed a positive association with egg production index in susceptible heifers (P<0.05) and a negative association in the resistant group (P<0.05), suggesting a host defense mechanism that reduces the conversion efficiency of ingested blood to eggs in engorged ticks from resistant cattle. This shows that bovine genetic tick resistance, in addition to affecting the number of ticks carried by the animals, also affected the egg mass weight, egg production and nutrient indexes of ticks. The results of the present study imply that the selection of resistant animals could be used as a strategic tool for tick control in production systems, reducing infestation levels on cattle and environment.

Use of molecular markers to improve relationship information in the genetic evaluation of beef cattle tick resistance under pedigree‐based models

“…Thus, the identification of genotypes that are resistant to this ectoparasite should be considered a selection objective (Biegelmeyer et al . ), as well as its relationship with other traits of economic interest (Turner et al . ).…”

“…Ticks are responsible for losses in the production system by damaging the health of cattle. Thus, the identification of genotypes that are resistant to this ectoparasite should be considered a selection objective (Biegelmeyer et al 2015), as well as its relationship with other traits of economic interest (Turner et al 2010). The misidentification of relationships decreases the accuracy of the selection of superior genotypes, and so the importance of using SNP information to warrant correct genetic relationships becomes crucial during this process.…”

Tag SNP selection for prediction of tick resistance in Brazilian Braford and Hereford cattle breeds using Bayesian methods

“…In total, 10,673 tick counts were available for analyses. Variance components and breeding values were generated from log-transformed tick counts [3, 18] with the BLUPf90 family of programs [19] and estimated breeding values were used for GWAS analyses.…”

“…In Brazil, the Rhipicephalus ( Boophilus ) microplus tick is one of the main causes of economic losses in cattle production and affects negatively the performance of their hosts both directly by blood sucking and indirectly as a vector of viral, bacterial and protozoal diseases [2]. Resistance to ticks is known to be under genetic control and the utility of genetic evaluations to classify cattle as resistant or susceptible based on natural tick infestations has already been demonstrated [3]. In addition, it is now well established that several biological mechanisms control host genetic resistance within and among breeds [4, 5].…”

Immune recognition of salivary proteins from the cattle tick Rhipicephalus microplus differs according to the genotype of the bovine host

“…Breeds of Bos indicus (indicine) cattle are more resistant to R. microplus than those of B. taurus (taurine) cattle, possibly because the former were domesticated in Asia [9, 10], which is also believed to be the place of origin of the parasite [11]. Even after they undergo repeated infestations, taurine breeds still remain susceptible to levels of tick loads that are unacceptable in terms of animal productivity and health [7, 8, 12–16]. Knowledge about the mechanisms involved in the hosts’ resistance to ticks will point to the path of new strategies of tick control.…”