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

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.