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

A randomized block design experiment involving thirty beef cattle (mean initial live weight 462 kg) was carried out to evaluate a bacterial inoculant based on a single strain of Lactobacillus plantarum as a silage additive and to provide further information in relation to its mode of action. Three herbages were harvested on 10 August 1989 using three double-chop forage harvesters from the first regrowth of a perennial 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 2.91 (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 respectively, 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 and 1.24 g (kg DM)-1. The silages were offered ad libitum and supplemented 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 gains 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), neutral detergent fibre (NDF) (P < 0.05) and energy (P < 0.05) digestibilities, the digestible organic matter concentration (P < 0.01) and the ME concentration (P < 0.05) of the total diets. Additive treatment altered rumen fermentation patterns but had little effect on the rumen degradability of silage DM, modified acid detergent (MAD) fibre, NDF or hemicellulose. It is concluded that treatment with the inoculant improved silage fermentation and increased digestibility, had little effect on silage DM intake but significantly increased carcass gain to a level similar to that sustained by a well-preserved formic acid-treated silage.