Using a real-time location system to detect behavioral changes in ewes with subclinical mastitis and their lambs

Abstract

Subclinical mastitis, the asymptomatic inflammation of the udder, is an important economic and animal welfare concern in meat-producing flocks, causing reduced milk yield and poorer lamb growth and survival. Cases often remain undetected until more severe stages, highlighting the need to investigate early detection methods, such as automated behavioral monitoring. Our objective was to use a real-time location system to determine whether subclinical mastitis affected ewe and lamb movement patterns. From 2–6 weeks postpartum, we collected duplicate milk samples weekly from each udder half of 24 ewes (15 Polypay, 3 Hampshire, and 6 Targhee) for bacterial speciation. Ewes were considered infected in a given week if milk samples from at least one udder half contained ≥ 100 CFU/mL at both the start of that week and the following week's sampling. Each ewe and her lamb(s) wore neck-mounted sensors that recorded x, y coordinates every 0.1 s via ultrawideband technology while housed in a group pen. We used linear mixed models to assess the effects of the ewe’s weekly infection status (healthy vs. infected) and weeks since lambing (2−6) on four behavioral outcomes: ewe-lamb distance, ewe-feed bunk distance, ewe distance traveled, and lamb distance traveled. The number of lambs reared (single vs. multiple) was included as a covariate and dam ID was specified as a random effect. Lambs traveled more during weeks when their dam was infected, possibly reflecting increased hunger due to insufficient maternal milk supply. No significant effects of infection status were observed for the other behavioral outcomes. Ewe–lamb and ewe–feed bunk distances were shortest, and lamb movement was greatest, in week 2 compared to later weeks – patterns that likely reflect the lamb’s greater nutritional dependence on the dam and increased play behavior early in life. Our findings provide preliminary evidence that real-time tracking of lamb behavior may help identify early cases of subclinical mastitis in the dam. They also highlight the potential welfare impacts of subclinical mastitis on lambs, underscoring the importance of early detection and management.