The effect of supplementary feeding on composition and renneting properties of milk from cows rotationally grazed at high altitude

Twenty-four early lactating cows grazed 77 d at high altitude and received concentrate providing either 0.5 or 1.0 of maintenance energy requirements with or without 1.0 of extra maintenance protein or no concentrate (controls). Accounting for lowland group differences, milk protein and renneting properties were improved by feeding 4 kg/d of a high energy/low protein supplement (protein +0.18 g/dl). Milk urea and somatic cell counts were also reduced compared to unfavourably high levels in controls. Additional protein increased milk urea to similar levels as controls and gave no real advantage for milk renneting properties, yet supported milk protein content. Contrasting with supplemented groups, controls maintained high milk fat content throughout the alp season. At mostly small treatment differences, milk Ca increased on the alp and P reduced whereas Mg, Na and K remained relatively constant. Grazing re-growth herbage of higher energy content in late season im proved milk protein and cheese making properties independent of concentrate effects.