Associations between <i>Theileria orientalis</i> Ikeda type infection and the growth rates and haematocrit of suckled beef calves in the North Island of New Zealand
Creators: name: KE Lawrence
name: BL Lawrence
name: RE Hickson
name: CA Hewitt
name: KR Gedye
name: LM Fermin
name: WE Pomroy
Publisher: name: Taylor & Francis
Year: 2018
Subjects: subject: Microbiology
subject: FOS: Biological sciences
subject: FOS: Biological sciences
subject: Genetics
subject: 39999 Chemical Sciences not elsewhere classified
subject: FOS: Chemical sciences
subject: FOS: Chemical sciences
subject: Ecology
subject: Science Policy
subject: Immunology
subject: FOS: Clinical medicine
subject: FOS: Clinical medicine
subject: 69999 Biological Sciences not elsewhere classified
subject: 110309 Infectious Diseases
subject: FOS: Health sciences
subject: FOS: Health sciences
subject: 60506 Virology
subject: Computational Biology

description: AIMS: The principle aim of this study was to examine the association between infection with <i>Theileria orientalis</i> Ikeda type and growth rates of suckled beef calves on four beef farms. In addition, associations between calf sex, sampling time, and individual farm and <i>T. orientalis</i> Ikeda type infection intensity and haematocrit (HCT) were investigated. METHODS: The study was a prospective longitudinal study in which 240 calves from four purposively selected beef farms in the North Island of New Zealand were blood sampled and weighed in late spring, mid-summer and early autumn. Two farms were from high-risk (A and B) and two from low-risk (C and D) tick areas. Blood samples were analysed to determine HCT, and the number of <i>T. orientalis</i> Ikeda type organisms/µL of blood (infection intensity) using a quantitative PCR assay. A calf was defined as infected if &gt;415 organisms/µL were detected in a blood sample. Linear mixed models were used to examine associations between infection intensity, mean daily liveweight gain (MDG), HCT, calf sex and time of sampling on the four farms. RESULTS: On Farms A and B nearly all calves were infected at each sampling time, on Farm C &lt;30% were infected at any sampling and on Farm D infection prevalence increased from 32 to 79% between late spring and early autumn. On Farms C and D, from mid-summer to early autumn, mean MDG was 0.127 (95% CI=0.072–0.183) kg/day less for infected than uninfected calves (p&lt;0.001). On all farms MDG was negatively associated with infection intensity for mid-summer and early autumn sampling times (p=0.037). The relationship between time of sampling and infection intensity varied between farms (p&lt;0.001), and between male and female calves (p=0.018). Females had a higher infection intensity than males at the mid-summer and early autumn samplings. The association between HCT and infection intensity varied with sampling time and farm (p=0.018). There was a strong negative association between infection intensity and HCT at the late spring sampling, but in mid-summer there was no association, and in early autumn only a weak association. CONCLUSIONS AND CLINICAL RELEVANCE: This study has shown that beef farmers in the North Island of New Zealand should be concerned about the welfare effects and economic impacts of <i>T. orientalis</i> Ikeda type infection in suckled beef calves.