Monitoring the Effect of Weed Encroachment on Cattle Behavior in Grazing Systems Using GPS Tracking Collars

SIMPLE SUMMARY: Pasture weed encroachment is a major challenge in livestock production based on grazing systems. Amaranthus spinosus L. is an annual weed species with high invasive potential worldwide, and it can affect animal behavior and well-being due to the presence of sharp spines. We used GPS tracking collars to monitor cattle activity and spatial distribution in a grazing system with different levels of weed encroachment. Animals in weed-infested paddocks had reduced resting time and increased grazing time, distance traveled, and rate of travel compared to animals in weed-free paddocks. The spatial distribution of the cattle was greater in weed-free paddocks than in weed-strips or weed-infested areas. Pasture weed encroachment affects cattle behavior and their spatial distribution across the pasture. Increasing animal activity can result in lower animal performance due to greater energy expenditure and impacts on animal welfare. Understanding the impact of pasture weed encroachment on animal behavior is especially important for increasing livestock productivity and sustainability while maintaining animal welfare. ABSTRACT: Weed encroachment on grasslands can negatively affect herbage allowance and animal behavior, impacting livestock production. We used low-cost GPS collars fitted to twenty-four Angus crossbred steers to evaluate the effects of different levels of weed encroachment on animal activities and spatial distribution. The experiment was established with a randomized complete block design, with three treatments and four blocks. The treatments were paddocks free of weeds (weed-free), paddocks with weeds established in alternated strips (weed-strips), and paddocks with weeds spread throughout the entire area (weed-infested). Animals in weed-infested paddocks had reduced resting time and increased grazing time, distance traveled, and rate of travel (p < 0.05) compared to animals in weed-free paddocks. The spatial distribution of the animals was consistently greater in weed-free paddocks than in weed-strips or weed-infested areas. The effects of weed encroachment on animal activities were minimized after weed senescence at the end of the growing season. Pasture weed encroachment affected cattle behavior and their spatial distribution across the pasture, potentially impacting animal welfare. Further long-term studies are encouraged to evaluate the impacts of weed encroachment on animal performance and to quantify the effects of behavioral changes on animal energy balance.