Three grass silages of different chop lengths made from a uniform sward of S23 perennial ryegrass were compared in four experiments including a feeding experiment with twelve lactating cows, an eating behaviour study, a rate of passage investigation and a selection trial. The silages had median chop lengths of 9-4. 17-4 and 720 mm, termed short, medium and long, with pH values of 3-93, 3-94 and 417 and D-values of 659, 65-2 and 64 4 respectively.The daily intakes of silage DM and the daily milk yields increased as silage chop length decreased. The milk yield response to shorter chopping was significant with a supplement of groundnut but not significant with a supplement of sugar-beet pulp. Chop length had small and generally non-significant effects on milk composition.Eating and ruminating times expressed as min per kg DM decreased as silage chop length decreased but the retention time ofthe silage residues in the entire digestive tract was not significantly affected by chop length. When offered simultaneously, the intakes of the individual silages were 52 2, 319 and 15 9% ofthe total DM intake for the short, medium and long treatments respectively.Although silage with a chop length of 9 mm had nutritional advantages over longer silages, it is concluded that the mechanical and economic aspects of silage making must be considered fully when defining optimum chop length.

Three first-harvest grass silages made from S23 perennial ryegrass cut on 25 May, 13 June and 25 June, and termed early, medium and late silages respectively, were compared in a 16-week feeding experiment with fourteen Ayrshire cows. The early, medium and late silages had Dvalues of 712, 650 and 62 5 respectively. The early silage was offered alone, whereas the medium and late silages were supplemented with a concentrate containing 208 g crude protein per kg DM at rates of 2, 3 and 4 kg per 10 kg milk. Silage DM intake was 12-8 kg per cow per d on the early silage treatment, and decreased progressively as concentrate intake increased on the other silage treatments. The mean daily milk yields were 16 0 kg per cow in the early silage treatment, 17-0, 18-4 and 20-4 kg per cow in the medium silage treatments, and 16 8, 181 and 20 2 kg per cow in the late silage treatments on the 2-, 3-and 4-kg concentrate treatments respectively. Fat concentration in the milk was not affected significantly by treatment, whereas the CP and SNF concentrations increased progressively and significantly as supplementary feeding increased. From the relationship between milk yield and concentrate intake it was calculated that the medium and late silages required a daily concentrate supplement of 21 kg DM per cow to give the same daily milk yields as the early silage.

Grass silage made in late May from S24 perennial ryegrass was offered to twelve Ayrshire cows in a 16-week feeding experiment. The silage had a DM content of 25-3%, a pH of 3-91, and contained 16-8% CP and 68-4% digestible organic matter in the DM. The silage was fed ad libitum and was the sole feed in the control treatment. In the other three treatments the silage was supplemented with a cube offered at rates of 0 8, 14 and 20 kg per 10 kg milk. The cube contained 82 2% groundnut, plus molasses and minerals, and had 37-9% CP in the DM. The daily intake of silage DM was 11 4 kg per cow on average over the four treatments which did not differ significantly. The mean daily milk yields were 14-8 kg per cow in the control treatment, and 16-5,18-2 and 18 4 kg in the 0 8,14 and 2 0 kg supplement treatments respectively. The SNF, CP and lactose contents of the milk were Wghest on the 14 kg supplement treatment. It is concluded that with a high digestibility silage, there is little evidence to support the feeding of more than 1-4 kg of highprotein cubes per 10 kg milk in the declining phase of lactation.

In three separate feeding experiments using a total of thirty individually-housed Ayrshire eows three silages made from perennial ryegrass were given ad libitum together with supplements of four different hays in the long form. The in vitro D-values of the silages ranged from 0-598 to 0-683, and the hays from 0-580 to 0-700, The daily intake of hay DM varied from 0-8 to 4-1 kg per cow and was given either without or with a daily maximum of 2-4 kg concentrate DM containing 379-527 g CP per kg DM, On average, 1 kg hay DM decreased silage intake by 0-84 kg DM with a range of 0-61-1-00 kg. The hay supplements had only small and non-significant effects on total DM intake, milk yield and milk composition, but increased the daily intake of drinking water. In three behavioural studies, the eating and ruminating times expressed as min per kg DM did not differ significantly between the various supplement treatments. It is concluded that hay has only a marginal value as a supplement for grass silage, although the hay could serve as a useful 'buffer' feed if the amount of silage was limited.

1977). A note on supplements for dairy cows offered silage of high digestibility.