Developing a New Tool for Phenotyping Tick Resistance in Cattle

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.

The proposed research will be of direct and indirect benefit to several groups and end-users beyond the academic community. Currently, beef and dairy cattle production in tropical and sub-tropical environments is characterized by numerous types of stress from ectoparasites (ticks, flies, other haematophagous arthropods), endoparasites (gastro-intestinal helminths, flukes, protozoa), seasonally poor nutrition, high heat and humidity and diseases that are often caused by a wide range of pathogens (bacteria, fungi, viruses). Under the extensive production systems common in the tropics, it is generally not possible to control the stressors through management strategies alone, and even if intervention strategies were feasible, the treatments often cause their own problems. Acaricides and anti-tick vaccines do not offer a permanent solution to tick control. Acaricide treatments used to control ticks are losing efficacy due to the rapid development of resistance of the parasites to acaricides, and acaricide use generates concern about residues in meat and milk products. Attempts to develop new anti-tick vaccines are ongoing but new vaccines are highly unlikely to confer total protection against ticks. The best method of reducing the impacts of these stressors to improve productivity and animal welfare is to breed cattle that are well-adapted to the different types of stress, and work in concert with other management interventions.

By providing resources to facilitate characterisation of the volatile semiochemical-based mechanism of host resistance against economically important tick species affecting cattle production in Kenya, the primary beneficiary in this project will be Kenyan agriculture. An understanding of the semiochemical basis of host resistance to ticks will underpin development of a new low-cost tool for phenotyping tick resistance in cattle, and will influence and enable the selection of animals to breed cattle that are resistant to ticks. Farmers in LMICs in tropical and sub-tropical environments other than Kenya will benefit where ticks and tick-borne diseases are a major constraint to livestock production. The development of a low-cost phenotype tool for selection and breeding of host resistance to ticks will provide a model that will assist stakeholders in Kenya, in other affected LMICs and in the UK, for phenotyping cattle for resistance to other ectoparasites, endoparasites, diseases and environmental stress.

Another key beneficiary of our work will be agribusinesses that recognise the need for the development of novel tick management interventions that can be integrated with other management interventions eg acaricides and vaccines, such that the lifetime of the latter interventions can be prolonged. Furthermore, through CTLGH-led activities, the knowledge and outputs from this project will inform and influence government and inter-governmental agencies, particularly those involved with tick management, on the need for genetic improvement of cattle with enhanced tick resistance.

The project will impact considerably at the environmental level. Tick management has traditionally been through acaricide usage. In addition to acaricide resistance, such chemicals carry a high environmental and human health impact, with chemical residue concerns, and their usage should be minimized. This project will move towards providing a solution to substitute these chemicals by a more sustainable, environmentally friendly solution.

The project will impact on the general public through more efficient and productive ruminant livestock industries, as this will lead to a more sustainable supply of high quality dairy and beef products. The public will also take comfort knowledge that animals are being farmed in a more welfare-friendly way. The public will also benefit in the medium term from decreased chemical usage, and in the long term from the contributions to decreased environmental impact from cattle production.