Hide ‘n seek: individual behavioural responses of cattle excreting different amounts of nematode eggs—potential threshold for pasture contamination assessment

Abstract

The aim of this study was to investigate how the activity of cattle under natural grazing conditions is related to their individual parasite contribution (IPC). Potentially, the individuals contributing the most to the contamination of the pasture with gastrointestinal nematodes (GIN) could then be identified and selectively treated based on sensor data thresholds. A total of 58 steers of the dairy breeds Swedish Red (SR, n = 19) and Swedish Holstein (SH, n = 39) were used for sensor-based data collection that lasted for a total of 10 weeks from 4 May to 13 July 2022. All steers were inoculated with a priming dose of nematode larvae and weighed in conjunction with the pasture release. The animals were then divided into four experimental groups and treated with ivermectin (IVM PO, Boehringer Ingelheim, 0.5 mg/kg BW) at different intervals to obtain an exposure contrast (Group A was left untreated, Group B/IVM PO-4w was treated after 4 weeks, Group C/IVM PO-8w was treated after 8 weeks, and Group D/IVM PO-4&8w was treated after 4 weeks and then after 8 weeks). The steers were weighed on four further occasions, during which faecal samples were also taken for parasite testing. Activity data were collected using leg-mounted IceQube sensors and body weight data and faecal samples were collected bi-weekly. The new threshold metric (IPC) was proposed for individuals with different faecal egg count (FEC) levels [NO (no contribution) <20 EPG, LO (low contribution) = 20–150 EPG, ME (medium contribution) = 150–250 EPG, and HI (high contribution) ≥250 EPG] The effects of IPC on activity patterns were analysed stepwise using a Generalised Estimating Equations model implemented in Python programming language. Results showed significant effects of different IPC values on motion index and number of steps taken (adjusted p-value of 0.008, 0.018, 0.041, and 0.001 for individuals with NO, LO, ME, and HI IPC values, respectively). There were some breed effects on the average number of steps and minutes spent lying. The results also provide alternative threshold methods aimed at finding more sustainable ways of using anthelmintics and integrating individual data into future parasite control strategies.