Developing a New Tool for Phenotyping Tick Resistance in Cattle

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In Kenya, cattle production on large commercial farms and smallholder farms provides an important source of protein, carbohydrates, fat, vitamins and minerals in the diet. Unfortunately, as with cattle reared in similar tropical and sub-tropical environments elsewhere in the world, many ticks attack cattle, causing severe losses from tick feeding damage and the spread of diseases. Although cattle can be protected from ticks by pesticides and even some alternative pest management tools eg anti-tick vaccines, most of the tools do not offer a permanent solution to tick management as they are neither completely effective nor sustainable. It is vital that new strategies to defend cattle production against ticks are developed.Cattle host resistance has been identified as the single most important factor affecting the economics of tick management, as it can be inherited and is low-cost requiring no extra labour or resources. However, improvements to host resistance in cattle are largely neglected because of difficulty and expense of identifying individual variation in resistance to ticks. A simpler, cost-effective method of identifying individual variation in resistance to ticks is urgently needed. One possible biological mechanism that could be used to identify such variation in resistance in ticks consists of cattle odour, which is used by ticks to locate a suitable host animal. Ticks use their sense of smell to detect and locate suitable host animals for blood-feeding prior to egg production. The odour of host animals comprises of attractive and repellent volatile compounds, and it has been shown that animals that are more resistant to ticks produce higher levels of repellent odours, compared to those animals that are less resistant. This ecological interaction can be exploited in livestock protection by using repellent odours to push ticks away from animals and using attractive odours to pull ticks into traps, or even using both sets of odours at the same time as part of a push-pull strategy.The use of synthetic repellent and attractive odours in pest management has been extensively explored, but this technology is not sustainable for extensive cattle production systems because protection is short-lived. A further development of the use of repellent odours is that they can be delivered by the animals themselves, with tick-resistant animals being selected to breed and create livestock that produce repellent odours. This approach to the delivery of repellents via hosts has been adopted with outstanding success in Africa for moth pest management on cereal crops, with more than 100,000 smallholder farms adopting it to date. Experiments under natural ie. farm conditions in Brazil using breeds of cattle called Nelore (tick-resistant), Holstein-Friesian (tick-susceptible) and Girolando (varying in its level of susceptibility to ticks) showed that tick resistance correlated with increasing levels of repellent odours eg. 6-methyl-5-hepten-2-one. If we can identify a similar correlation between tick resistance in Kenyan breeds of cattle with levels of repellent odours, then we have an opportunity to develop a new way of identifying tick resistance in cattle that is more cost-effective than current methods, and which can be used to select tick-resistant animals for breeding tick resistance based on repellent odours.We will screen, under controlled conditions, Kenyan cattle to ascertain their resistance to ticks; screen, in the field, Kenyan cattle for their resistance to natural tick populations; screen, under these controlled and natural conditions, the production of repellent odours and demonstrate a correlation between tick resistance and repellent odour production; explain, to farmers, cattle breeders and other relevant parties, our new approach to the selection of tick-resistant animals for breeding tick resistance, based on repellent odour production.