EFFECTS OF TREATING LOW DRY-MATTER GRASS WITH A BACTERIAL INOCULANT ON THE INTAKE AND PERFORMANCE OF BEEF-CATTLE AND STUDIES ON ITS MODE OFACTION

A randomized block design experiment involving thirty beef cattle (mea n initial live weight 462 kg) was carried out to evaluate a bacterial inoculant based on a single strain of Lactobacillus plantarum as a sil age additive and to provide further information in relation to its mod e of action. Three herbages were harvested on 10 August 1989 using thr ee double-chop forage harvesters from the first regrowth of a perennia l ryegrass sward which had received 170 kg N, 25 kg P2O5 and 42 kg K2O ha-1. They received either no additive (silage C), formic acid at 2.9 1 (t grass)-1 (silage F) or the inoculant at 3.21 (t grass)-1 (silage I). Mean dry-matter (DM), water-soluble carbohydrate and crude protein concentrations in the untreated herbages were 158 g kg-1, 88 g (kg DM )-1 and 183 g (kg DM)-1 respectively. For silages C, F and I respectiv ely, pH values were 4.01, 3.57 and 3.62; ammonia N concentrations 117, 55 and 77 g (kg total N)-1; and butyrate concentrations 2.18, 0.50 an d 1.24 g (kg DM)-1. The silages were offered ad libitum and supplement ed with 2.5 kg concentrates per head daily for 77 days. For treatments C, F and I, silage DM intakes were 6.59, 7.25 and 6.80 (s.e. 0.074)kg d-1; metabolizable energy (ME) intakes 86,99 and 94 (s.e. 0.8) MJ d-1 ; liveweight gains 0.90, 0.97 and 1.02 (s.e. 0.066) kg d-1; carcass ga ins 541, 656 and 680 (s.e. 34.0) g d-1. Inoculant treatment increased DM (P < 0.01), organic matter (P < 0.01), crude fibre (P < 0.05), neut ral detergent fibre (NDF) (P < 0.05) and energy (P < 0.05) digestibili ties, the digestible organic matter concentration (P < 0.01) and the M E concentration (P < 0.05) of the total diets. Additive treatment alte red rumen fermentation patterns but had little effect on the rumen deg radability of silage DM, modified acid detergent (MAD) fibre, NDF or h emicellulose. It is concluded that treatment with the inoculant improv ed silage fermentation and increased digestibility, had little effect on silage DM intake but significantly increased carcass gain to a leve l similar to that sustained by a well-preserved formic acid-treated si lage.