Abstract
In India, disease of cattle caused by tick-borne pathogens (TBP) constrains the rearing of high yielding Bos taurus dairy breeds that often develop clinical, fatal disease. Bos indicus and bufflao show resistance to TBP infection, and this has led to a policy of rearing crossbred indicus-taurus cattle. On dairy farms, co-grazing more resistant animals alongside crossbreeds could contribute positively (by removing potentially infective ticks) or negatively (by acting as a reservoir for infection). We investigated epidemiological factors that contribute to the prevalence of five tick-borne pathogens with links to milk-yield in co-grazed host types in dairy farms of two regions of Tamil Nadu, India; a region of high dairy production importance. A high prevalence of T. annulata and Anaplasma spp. was detected, but with lower prevalence in the Cauvery Delta than in the Northwestern zone. A strict host-type association with prevalence was observed: buffaloes had lower prevalence of TBP than cattle; and native breeds had a lower prevalence of Anaplasma spp. than crossbreeds. The results indicate that while susceptibility to becoming a carrier animal for TBP depends on exposure to ticks; aspects of resistance are determined by host type independent of tick exposure. There was no clear evidence that co-grazing, with more resistant host types, will provide a positive contribution (protective effect) to crossbreeds with greater milk productivity.
Highlights
Tropical bovine theileriosis is a tick-borne disease (TBD) caused by Theileria annulata belonging to the phylum Apicomplexa
Results of the PCR assay for T. annulata were initially correlated with location and host type: 76.2%, 68.0% and 26.4% of crossbred cattle, native cattle and buffaloes, respectively from the North Western region were infected, and 67.1%, 54.5% and 4.0% in crossbred cattle, native cattle and buffaloes
We found a significant impact of sex on prevalence of Anaplasma, this result should be treated with caution: male crossbreed cows and buffalos are not kept on farms, as they are considered uneconomic, while male native breeds are kept for labour purposes
Summary
Tropical bovine theileriosis is a tick-borne disease (TBD) caused by Theileria annulata belonging to the phylum Apicomplexa. In India, the dairy industry is important (estimated 160 million metric tonnes in 2017), but the prevalence of cattle infected with tick-borne pathogens (TBP) can be high and constrains the rearing of high-yielding Bos taurus breeds. A recent survey carried out in Maharashtra state, India showed that the fitness cost to apparently healthy animals with subclinical infection of tick-borne haemoparasites (Theileria and Babesia) were more pronounced in crossbreed than in native breed cattle [6]. Such losses are of importance in India, where a growing population relies on dairy products as a primary source of protein [1]
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