A comparison of low starch maize silage and grass silage and the effect of concentrate supplementation of the forages or inclusion of maize grain with the maize silage on milk production by dairy cows

Abstract

This experiment examined the effect of partially replacing (60%) a high quality grass silage (GS) with an immature, low starch maize silage (LSM) on forage intake and milk production by dairy cows. The responses in milk production and composition to increased concentrate supplementation (4, 6 or 8 kg/cow/day) of these forages were also determined. An additional treatment (HGM, high grain maize silage) in which ground maize grain was incorporated with the LSM silage prior to feeding to increase the starch content of the forage was included in the experiment. The HGM forage was mixed with the GS silage (60:40) and supplemented with one level of concentrates (4 kg/cow/day). The experiment involved 56 Holstein-Friesian cows, 28 in early lactation and 28 in mid-lactation, in a randomised block design (eight cows/treatment) for a period of 7 weeks. The composition of the GS and LSM silages and HGM forage, respectively, were as follows: dry matter (DM) 192, 228 and 331 g/kg; crude protein (CP) 183, 124 and 116 g/kg DM; starch 13, 15 and 355 g/kg DM; in vitro DM digestibility 755, 703 and 754 g/kg; pH 4.0, 3.8 and 3.9; and ammonia N 69, 53 and 36 g/kg total N. The concentrate contained 288 g CP/kg DM, 139 g starch/kg DM and 12.5 MJ metabolisable energy (ME)/kg DM. Replacing the GS silage with the LSM silage increased forage intake (11.2 vs 9.5 kg DM/day, S.E.M. 0.25, P<0.001) but had no significant effect on yields of milk, fat, protein, lactose or on fat concentration. Milk protein concentration was higher on the LSM forage (32.6 vs 31.5 g/kg, S.E.M. 0.18, P<0.001). Increasing the level of concentrates reduced intake of GS silage but tended to increase the intake of the LSM forage, and linearly increased the yields of milk, milk constituents and milk protein concentration ( P<0.001) for both forages. Milk yield was increased to a greater extent by concentrate supplementation of the GS silage compared with the LSM forage (0.92 vs 0.43 kg milk/kg concentrate DM) whereas yield of fat and protein was increased to a similar extent for both types of forage (65 vs 58 g/kg concentrate DM). Increasing the level of starch in the HGM forage increased forage intake (13.4, 10.2, and 10.6 DM/day, S.E.M. 0.46, P<0.001) and milk yield (21.9, 19.7, and 20.4 g/day, S.E.M. 0.49, P<0.01) compared with the GS and LSM forage at the low level of concentrate supplementation. The yields of fat, protein and lactose and milk protein concentration were also higher on the HGM forage. An additional 2.6 or 3.5 kg concentrates/day would need to be fed with the GS and LSM forages, respectively, to achieve the same yield of milk as obtained with the HGM forage and 4 kg concentrates/day. One kg DM of maize grain in the HGM forage was equivalent to 0.85 or 0.79 kg concentrate DM as supplements to the LSM or GS forages, respectively, for milk production. It was concluded that an immature low starch maize silage, when harvested in a green state with a high digestibility, was equivalent to a high quality grass silage in terms of milk production, but feed efficiency for milk production was reduced. Increased concentrate supplementation resulted in a similar response in the yield of fat and protein with both types of forage. Increasing the level of starch in immature maize silage, by adding maize grain to achieve a level of starch similar to a very mature maize silage, has the potential to increase feed intake, milk production and milk protein concentration. Alternatively, the level of concentrates fed with the high starch forage can be reduced by 3 kg/day compared with the grass silage or low starch maize forage, while maintaining the same level of milk production.