Behavioural indices as means of assessing buffalo fly numbers on cattle

Buffalo flies (BF), Haematobia irritans exigua, cause more than $100 million annual loss to the Australian cattle industries in terms of losses in weight gain, milk production and skin value and management costs. In addition, irritation and annoyance due to biting of BF have significant welfare impacts. Current BF control measures are heavily reliant on chemical treatments, but resistance to chemicals is widespread. Breeding cattle resistant to BF could help reduce BF impacts and costs of production. Although there is well documented variation among cattle in susceptibility to BF, accurately phenotyping animals for BF resistance is difficult and practical methods of assessing resistance are needed for use in selection and breeding programs.

Infestations of BF cause a range of protective behavioural responses in cattle, including tail flicks, head tosses, ear flicks, leg stomps and skin twitching. Behavioural responses have been shown to be correlated with parasite numbers in a number of other host-ectoparasite systems and may provide a more practical and potentially more accurate method of estimating buffalo fly susceptibility in cattle than the use of direct BF counts.

This study assessed the relationship between BF numbers and BF avoidance behaviours with a view to the use of automated measurement of behaviours by methods such as accelerometer ear tags, as an indicator of BF resistance. Buffalo fly numbers on 34, 2-year-old Brangus steers were recorded by visual and photographic techniques on nine different dates during the BF season in 2020 and 2021. Average BF count across the nine dates was used as an estimate of BF susceptibility for each animal. In addition, the behaviours of individual steers were recorded visually by an observer in 2-min periods in the morning of each observation day. Animals were observed in groups of five in an open fenced area from a distance of 3–5 m.