GRASS-SILAGE AS A BASIC FEED FOR STORE LAMBS .3. EFFECT OF BARLEY SUPPLEMENTATION OF SILAGES VARYING IN CHOP LENGTH ON SILAGE INTAKE AND LAMB PERFORMANCE

An experiment was carried out to study the effect of silage chop lengt h and barley supplementation on silage intake and the performance of s tore lambs. The silages were cut from a perennial ryegrass regrowth at a relatively mature stage of growth in early July. Different types of harvester were used to produce a long silage (L), single-chopped (S), double-chopped (D), medium precision-chopped (MP) or a short precisio n-chopped (SP) silage. The chop length of the silages averaged 37.4, 1 2.4, 8.4, 7.0 and 2.9 cm respectively. All silages were treated with f ormic acid at 2.51 t(-1) grass. They were well preserved and of a good quality with a dry-matter (DM) digestibility of 720-760 g kg(-1) DM. The silages were fed ad libitum to Suffolk crossbred store lambs over a period of 10 weeks. Each silage was fed either alone or was suppleme nted with whole barley at 400 g lamb(-1) d(-1). When offered silage al one, intakes were 738, 679, 773, 980 and 910 (+/-30) g DM d(-1) for si lages L, S, D, MP and SP respectively. Similar relative differences in intakes between the silages were evident when supplemented with barle y. Liveweight gain on silage alone was higher on the precision-chopped silages (85-93 g d(-1)) than the long or flail-chopped silages (28-49 g d(-1)). Liveweight gain on the precision-chopped silages was also b etter when supplemented with barley (150 vs. 90-112 (+/-9.0) g d(-1)). Silage intake and lamb performance were similar for the MP and SP sil ages, despite the difference in chop length. Barley supplementation re duced silage intake to a similar extent for all silages (-9%) and incr eased total DM intake (+30%) and metabolizable energy intake (+37%). T he substitution rates of silage for barley were similar for all silage s and averaged 0.24 g silage DM g(-1) barley DM. The response in weigh t gain per 100 g of barley fed was similar for all silages and average d 20.0 g liveweight gain and 13.4 g carcass gain. Feed conversion effi ciency of the total diet was similar for the hail-chopped and precisio n-chopped silages but was less for the long silage. The results of thi s study show that the benefit in weight gain due to the higher intake of precision-chopped silage was maintained when the silage was supplem ented with a moderate level of barley. Such silage required supplement ation with barley (400 g d(-1)) to achieve a rate of liveweight gain o f 150 g d(-1).