Don't let milk output go extinct: postgrazing sward height shapes dairy cow foraging efficiency

Postgrazing sward height is a key management factor in dairy cattle grazing systems because it governs bite formation, subsequent canopy structure, and the trade-off between forage selectivity and harvest efficiency. This study evaluated how postgrazing sward height shapes ingestive behaviour across temporal (bite, meal, day) and spatial (feeding station) scales and how these responses relate to grazed forage intake and milk production of grazing cows in mixed-feeding dairy systems. Thirty-two multiparous Holstein cows grazed tall fescue (Lolium arundinaceum) under two treatments: Control (5.0-7.0 cm) and High (12.0-15.0 cm) postgrazing residuals, arranged in a randomised complete block design (4 blocks × 2 paddocks of 1.6 ha). Detailed 5-day measurements were performed in winter (Period I) and spring (Period II), when cows grazed for 6.5 and 8.0 h/day, respectively, and received a mixed ration after pasture access. Daily grazing time averaged ∼300 min/cow and did not differ between treatments, but was ∼1 h longer in Period II. Cows at the High treatment distributed grazing into shorter, more frequent meals (2.6 vs 3.1 meals/d). At the spatial scale, they visited more feeding stations, spent less time per feeding station and took fewer but larger bites, displaying a rapid-sampling grazing strategy. These behavioural adjustments increased the efficiency and selectivity of forage harvesting. In Period I, cows at the High residual achieved a 32% greater grazed forage intake rate and consumed 2.0 kg DM/cow per day more grazed forage and leading to an increased total DM intake without increasing daily grazing time. Across both periods, they selected forage with higher CP (+55 g/kg DM) and lower fibre (-17 g NDF and -31 g ADF/kg DM) than Control cows, resulting in 10% greater milk production at equal supplementation. Postgrazing sward height influences the temporal and spatial behavioural mechanisms by which grazing dairy cows acquire nutrients and highlights the importance of considering these behavioural responses when designing sward management strategies to improve nutrient capture and use efficiency.