At grazing, the nutritive value of grass offered to the dairy cow is like a ‘natural’ total mixed ration
Résumé
At grazing, the nutritive value of grass offered is, together with intake, the key component of feed supply, which is an important driver of animal performance. A large database of 1052 samples of grass offered at grazing to dairy cows has been created to describe the chemical composition and nutritive value and to examine some factors of variation along the year. The samples were collected during multiyears experiments (1995-2019) at the INRAE Le Pin experimental farm (Normandy). The database contains chemical composition including dry matter (DM), organic matter (OM), crude protein (CP), fibre contents (CF, NDF-ADF) and pepsin-cellulase digestibility. The INRA 2018 equations have been used to calculate the OM digestibility (OMd), the fill unit for dairy cows (UEL), the net energy for milk (UFL) and protein digestible in the intestine (PDI) values. On average, the OM, CP and CF, NDF and ADF contents are 895±23.7, 180±32.6, 225±25.5, 513±26.3 and 257±23.9 g kg-1 DM, respectively. The variation of grass composition and feed value is partly explained by season and pre-grazing pasture characteristics. With a UFL and PDI average value of 0.95±0.08 and 99±8.1 g kg-1 DM, well managed grazed grass has similar composition to a total mixed ration and is self-sufficient in feeding dairy cows.