Partial storage feeding (grazing during the daytime and housing overnight) is becoming an established management system after turnout in the spring. Ad libitum grass silage is the most common overnight feed. However, some farmers do not have adequate silage available and a straw mix is a possible alternative feed. There is little information available concerning the optimum energy content of straw mixes (or other forages) used for partial storage feeding. In this experiment 3 straw mixes were fed with different energy contents.

In a continuous design experiment lasting 8 weeks (18 April to 12 June 1985) 60 autumn calving Friesian dairy cows and heifers were set stocked together during the daytime at 10 cows/ha. They were housed overnight and straw mixes, with low (L), medium (M) or high (H) metabolisable energy (ME) contents, were fed ad libitum each to 20 cows. In addition an average of 2.3 kg concentrates were offered daily. The grazing area was a perennial ryegrass ley which received 224 kg N, 13 kg P2O5 and 13 kg K2O/ha. The mean composition of the straw mixes, herbage and concentrate are given in Tables 1 and 2.