ABSTRACT
Summary The main objective of our research was to measure the intake and digestibility of grass silages in order to estimate their potential for meeting requirements for maintenance and milk production. Twelve silages were prepared by the following three techniques, which considerably improve the intake compared with those used 10-20 years ago: (1) fine chopping (1-3 cm), (2) adding formic acid as an efficient preservative (3.5 1/ton), and (3) covering the roughages with plastic to prevent oxygen from entering the silo. Three other silages were made simultaneously with 3 of the same forages, but without formic acid. All forages were directly cut and ensiled into 100-m3 bunker silos. All trials were carried out in winter, with silages fed ad libitum to groups of 8-12 cows from the second to fifth month after calving. The amount of concentrates fed was predetermined to meet the total requirements by taking into account silage intake, silage digestibility, milk production at the beginning of the experiment, and predicted milk production. Elsewhere 2 of 12 formic acid silages were also fed with 1 kg concentrate more and with 1 kg concentrate less. Experimental periods lasted 10-13 weeks, allowing variations in live weight to be measured. The 12 silages with formic acid were well preserved and had a high organic-matter digestibility (72.4%). Ingested DM of silages and concentrates was 2.09 and 0.59 kg/100 kg live weight, respectively, for cows producing 19.5 kg fat-corrected milk with a daily live-weight gain of 126 g. When no formic acid was used, silage intake decreased considerably (- 12.6%), partly due to a greater distribution of concentrates. Indeed, for the two silages fed with different level of concentrates, DM intake dropped 0.5 kg when a 1-kg DM increase in concentrates was made. Net energy provided by fine-chopped silages preserved with formic acid was enough to cover maintenance needs and a mean production of 12 kg of milk/cow (from 5 kg for late cut to 17 kg for early cut). For 5 silages of perennial ryegrass at first growth this milk-production potential was 15 kg for an organic-matter digestibility of 74.7%. Milk potential decreased by 2 kg when silages without formic acid were given and had to be compensated for by concentrates. Therefore, if grass silages are perfectly prepared at an early stage of growth, their feeding value can be very high. Moreover, these grass silages generally can sustain the same level of milk production with nitrogen as with net energy.
