Comparing Individual Grass Intake of Dairy Cows in 3 Grass-Based Systems Using 3 Methods: Automated Weighing Bins, Net Energy Evaluation, and n-Alkanes

Abstract

Estimating fresh grass intake of grazing cows is important for effective management, but direct measurements are inherently difficult in grazing systems. Therefore, this study compared 3 methods to estimate fresh grass intake of dairy cows: automated weighing bins (Roughage Intake Control; RIC), net energy evaluation (VEM), and n-alkanes. A grazing trial was performed in 3 periods with 3 different grass-based systems: restricted zero-grazing (ZG), restricted grazing (RG), and unrestricted grazing (UG). For the VEM method, energy requirements and intake and VEM content of grass were used. For the n-alkane method, C32 and C36 were supplied to the cows, and faecal samples were collected. For ZG cows, RIC indicated a higher fresh grass DMI (9.6 kg cow⁻¹ day⁻¹) compared with VEM (9.3 kg cow⁻¹ day⁻¹) and n-alkanes (8.4 kg cow⁻¹ day⁻¹). For all groups and periods, VEM resulted in a higher DMI (11.2 kg cow⁻¹ day⁻¹) compared with n-alkanes (9.6 kg cow⁻¹ day⁻¹). Methods did not show high correlations, but differences in the estimation of DMI were relatively small. With the n-alkane method, intake is estimated via natural markers, reflecting environmental and behavioural factors for grazing cows, possibly giving a better reflection of individual variation in grazing behaviour among cows compared with VEM. Concluding, either the VEM method or the n-alkanes method may be used to estimate fresh grass DMI of individual dairy cows grazing in groups, depending on the study context.