Effects of replacing grass silage with maize silages, differing in maturity, on performance and potential concentrate sparing effect of dairy cows offered two feed value grass silages

A partially balanced change-over design experiment, consisting of four 3-week periods, was undertaken to evaluate the effects of stage of maturity of maize silage at harvest, when included in the forage component of two contrasting feed value grass silage based diets offered to 24 lactating dairy cows, on animal performance and potential concentrate sparing effect. Four maize silages were ensiled which had dry matter (DM) concentrations of 202, 280, 298 and 384 g/kg and starch concentrations of 100, 273, 270 and 332 g/kg DM, respectively. Low (L) and high (H) feed value grass silages were ensiled from the primary growth of predominantly perennial ryegrass swards. For the L and H feed value grass silages, DM concentrations were 193 and 326 g/kg and metabolisable energy (ME) concentrations were 9.80 and 11.96 MJ/kg DM, respectively. The grass silages were offered either as the sole forage supplemented with 7 or 11 kg concentrate/cow daily or in addition to one of the four maize silages at a ratio of 40:60, on a DM basis, maize silage: grass silage supplemented with 7 kg concentrate/cow daily. The forages were offered ad-libitum. There were no interactions (P > 0.05) between grass silage feed value and maturity of maize at harvest for food intake or animal performance. For the grass silage supplemented with 7 and I 1 kg concentrate and the 202, 280, 298 and 384 g/kg maize silages, total DM intakes were 16.9, 19.0, 18.2, 18.5, 18.1 and 18.4 (s.e. 0.31) kg/day; milk yields were 26.8, 29.9, 27.2, 28.0, 27.5 and 27.8 (s.e. 0.37) kg/day; milk fat concentrations were 39.8, 39.0, 42.4, 41.7, 41.4 and 40.2 g/kg; and milk protein concentrations were 31.5, 32.7, 32.3, 32.4, 32.1 and 32.5, respectively. The potential concentrate sparing effects of the maize silages with DM concentrations of 202, 280, 298 and 384 g/kg, as determined by fat plus protein yield, were 2.1, 3.4, 2.1 and 2.0 kg fresh weight, respectively. It is concluded that including maize silage in grass silage based diets improved milk output due to increased ME intake. There are no interactions between grass silage feed value and maturity of maize at harvest on subsequent animal performance. The optimum stage of maturity to harvest maize silage for feeding to dairy cows is approximately 300 g/kg. There is a negative relationship between maturity of maize silage and milk fat concentration. The potential concentrate sparing effect of including maize silage as 0.40 of the forage component of grass silage based diets is up to 3.4 kg/cow daily. (C) 2008 Elsevier B.V. All rights reserved.