Exploring the impact of grazing intensity and duration on dairy cow production and health.

Dairy cow grazing is widely appreciated by society due to its perceived benefits for animal welfare and health. However, concerns about dairy cow health are also cited as reasons for adopting year-round confinement systems. Comprehensive assessments on the relation of grazing intensity and duration (GID) with dairy cow production and health under practical conditions are lacking. This exploratory, longitudinal observational field study assessed the association between grazing parameters and production and health indicators in 70 commercial Dutch dairy herds during the 2023 and 2024 grazing seasons. Studied GID parameters included grazing hours, grazing days, average daily grazing hours (ADGH), restricted versus unrestricted grazing, and cow-hours per hectare available for grazing (CH/ha). Collected farm data included indicators of production (standardized milk yield, fat and protein content), udder health (bulk milk SCC), parasitic infections (antibodies to Dictyocaulus viviparus and Ostertagia ostertagi), and claw health (antibodies to Treponema spp.). Compared with the pregrazing season (∼6 wk before turnout), the grazing season was associated with slightly lower milk production and slightly poorer udder health, whereas fewer farms tested positive for Treponema spp. antibodies. Standardized milk yield showed a small negative association with GID, whereas fat and protein content were positively associated. More CH/ha was linked to lower bulk milk SCC. Grazing hours and ADGH were associated with increased odds of infection with D. viviparus and O. ostertagi. Unrestricted grazing (pasture access for ≥17.5 h/d and ≥30 consecutive days) was associated with higher odds for D. viviparus antibodies and more CH/ha with O. ostertagi antibodies. No GID parameters were associated with Treponema spp. antibodies. Although associations were modest and based on univariable analyses, the findings offer novel insights into how different grazing practices may affect production and health in commercial dairy herds with seasonal pasture access.