Influence of cutting frequency in Alpine permanent grassland on nutritive value, DM yield and agronomic parameters

The objective of the study was to investigate the impact of cutting frequency and fertilisation on yield and nutrient content in Alpine permanent grassland as well as on agronomic parameters of milk production with dairy cows depending on these grassland management factors. The experiment was based on a 3 x 3 two-factorial design, consisting of 3 levels of cutting frequency (2, 3, 4 cuts per year) and 3 levels of fertilisation (80, 160, 240 kg N per hectare). The nutrients were supplied both by liquid manure (15, 30 and 45 ml per ha) and mineral fertilizers. Cutting frequency showed a highly significant impact on an all nutrient parameters investigated (10.5, 13.0, 16.4 percent CP; 60.0, 52.4, 45.1 percent NDF; 54.4, 65.7, 74.2 percent dOM in vitro; 69.1, 75.9, 82.1 percent in situ DM degradability). DM yield was highest at medium cutting frequency (10717, 11198, 10756 kg DM), but differences were not great, although significant. Based on the results of the grassland experiment, model calculations were carried out for both a feeding regime without concentrate and a concentrate supply according to animal requirements. The impact of forage quality on feed intake is of major consequence. By higher forage intake - accompanied with lower DM yield of grassland - the possible stocking rate is significantly reduced with cutting frequency (1.62, 1.60, 1.47 and 2.21, 1.87, 1.55 cows per ha with the two concentrate levels). From this it follows that the improved feed intake (and therefore milk yield) on animal level does not necessarily result in higher milk productivity on area level (i.e. milk yield per hectare). The same is true for N excretion. Furthermore, there is a significant interaction between cutting frequency of grassland and concentrate level in dairy cow feeding. At low concentrate levels, the increase of individual milk yield and N excretion exceeds the effect of the reduced stocking rate, resulting in higher milk yield (4654, 7049, 8310 kg) and N excretion (127, 149, 181 kg) per hectare forage area. The opposite is true for concentrate levels necessary to fulfil nutrient requirements of the cows. The highest milk yield (14207, 12003, 10118 kg) and N excretion (207, 183, 189 kg) per hectare forage area can be expected at low cutting frequency. However, when the results are related to the total area necessary for milk production (i.e. forage plus concentrates), the highest milk yield and N excretion is achieved with high cutting frequency of grassland. It is concluded that optimal cutting frequency of permanent grassland has to consider a sustainable grassland management aiming at a stable botanical composition, nutrient content, DM yield and dense swards. From the viewpoint of dairy cow nutrition, the forage quality required to feed dairy cows has to be enhanced in proportion with the intended milk yield.