Behavioral changes in dairy cows feed-supplemented with 3-nitrooxypropanol: a pilot study

The feed additive 3-nitrooxypropanol (3-NOP; Bovaer®), approved in the EU for reducing enteric methane emissions in cattle, has shown side effects in terms of reduced feed intake, which raises animal welfare concerns. This study investigated behavioral effects of 3-NOP (60 mg/kg DM) in 46 healthy, loose-housed, primiparous Danish Holstein cows. As part of a larger experiment following a 3 × 3 Latin square design with 3 periods, each consisting of 14 days of adaptation and 7 days of sampling, cows received 3-NOP, nitrate (not analyzed herein), or control diets in partially mixed rations based on maize and grass clover silage. Cows were dynamically grouped into 2 sections dimensioned for housing 24 cows/section. Cow behavior was video-recorded and labeled using focal animal sampling and 1-min instantaneous recording on days 18 and 20 (daily periods: 10.00 h to 13.00 h, 20.00 h to 23.00 h) during each of the 2 periods of interest. The percentages of instantaneous recording (scans) of each behavior, as well as daily feed intake, were analyzed with LMM and GLMM in R. When supplemented with 3-NOP, cows spent less time in upright posture (standing still or in motion) (52.6 vs. 56.8% of scans/6 h/day; P < 0.05) and showed suggestive trends toward increased lying time (34.8 vs. 31.5% of scans/6 h/day; P = 0.095) and increased vigilance (odds ratio ± SE for 3-NOP vs. Control = 5.3 ± 4.8; P = 0.067). Given the concurrent 4.5% reduction in feed intake (16.9 vs. 17.7 kg/d; P < 0.01), these subtle behavioral changes, detected approximately 3 weeks after treatment start, warrant further examination of the behavioral and welfare effects of 3-NOP supplementation on dairy cattle, including 24‑h behavioral observations.