Influence of herbage allowance or of the level of Nitrogen fertilization on the performances of dairy cows

摘要

A grazing trial with dairy cows was conducted during three years; two levels of herbage allowance were compared, one with 15 kg DM and one with 20 kg DM per cow per day (with the same amount of N, 50 units, applied on the swards at each grazing cycle in spring); two levels of N application were also compared: 50 and 25 units per ha at each grazing cycle in spring (with the same herbage allowance: 15 kg DM per cow per day); the pastures were Perennial ryegrass swards. The cows were turned out to grass at the end of March under a 12-paddock rotational grazing system. Milk production at turn out was about 28 kg per day with 42 percent butterfat and 30 percent protein. Milk production was significantly greater (22.6 kg/day) at the 20 kg DM herbage allowance level than at the 15 kg DM level (21.3 kg milk/day). The butterfat content was lower at the higher herbage allowance level, while the protein content did not vary with herbage allowance. Reducing the N fertilization at the same level of herbage allowance (15 kg) had no influence on either the milk yield or the milk composition.