Concentrate supplementation of grazing dairy cows. 2. Effect of concentrate composition on herbage intake and milk production

The effect of feeding either traditional concentrates containing starch or high quality fibrous concentrates on the performance of grazing dairy cows was examined in a trial in which cows were given concentrates with either 350 g starch and sugars (kg dry matter (DM))‐1 (high‐starch) or 100 g starch and sugars (kg DM)‐1 (high‐fibre). The swards used consisted predominantly of perennial ryegrass and were usually aftermaths following cutting. Each area was grazed for 3 or 4 d at each grazing and a two‐machine sward‐cutting technique was used for estimating herbage intake. The effect of concentrate composition on the herbage intake of grazing cows at a high daily herbage allowance of 28 kg OM above 4 cm cutting height was investigated in 1983 and 1984. With 54 kg OM d‐1 of high‐starch concentrates the mean herbage intake was 11·5 kg OM d‐1 per cow while cows fed 5.3 kg d‐1 of high‐fibre concentrates consumed on average 12–6 kg OM d‐1. The mean substitution rate of herbage by concentrates was reduced from 0·45 kg herbage OM (kg concentrate OM)‐1 with the high‐starch concentrate to 0·21 with the high‐fibre concentrates. The effect of the treatments on milk production was studied in 1984. The cows consumed 5·5 kg OM d‐1 as concentrates and grazed at a lower herbage allowance of 19 kg OM above 4 cm cutting height. With high‐fibre concentrates milk production and 4% fat‐corrected milk production were 13 and 1·8 kg d‐1, respectively, higher than with the high‐starch treatment. The daily live weight gain with the high‐starch concentrates was 0·17 kg per cow more than with the high‐fibre concentrates.