Evaluation studies in the development of a commercial bacterial inoculant as an additive for grass silage

A randomized‐block experiment was carried out to evaluate a bacterial inoculant, based on a single strain of the organism Lactobacillus plantarum, as a silage additive. The inoculant‐treated silage was compared with untreated and formic acid‐treated silages. The three silages were harvested from a perennial ryegrass sward on 30 September and 1 October, 1985 using two double‐chop forage harvesters. Formic acid (850 g kg−1) was applied at a rate of 31t−1 and the inoculant at a rate of 3 g mixed in 31 water t−1 (1 × 106 colony forming units (g grass)−1). The dry matter and water‐soluble carbohydrate contents of the grass at ensiling were 165 g kg−1 and 18·9 g kg−1 respectively. For a period of 84 d, the three silages were offered ad libitum and supplemented with three concentrates in a 3 × 3 factorial design to 63 male cattle which were initially 15 weeks old and 128 kg live weight. The three concentrates were (1) barley (115 g crude protein (CP) (kg DM)−1), (2) barley/soyabean meal (207 g CP (kg DM)−1) and (3) barley/fish meal (200 g CP (kg DM)−1); each was offered at a mean rate of 1·7 kg d−1. For the untreated, formic acid‐treated and inoculant‐treated silages respectively, ammonia‐N concentrations were 162, 91 and 176±60 g (kg total N)−1; pH's were 4·48, 3·89 and 4·45±0·046; butyric acid contents were 12·1, 1·3and 16·6g(kg DM)−1; metabolizable energy contents were 12·4, 12·2 and 1·23±0·29 MJ (kg DM)−1; silage DM intakes were 2·28, 2·49 and 2·44±0·037 kg d−1 and liveweight gains were 0·90, 0·95 and 0·97±0·023 kg d−1. For the barley, barley/soyabean meal and barley/fishmeal supplements respectively, silage DM intakes were 2·29, 2·43 and 2·49 ± 0·037 kg d−1 and liveweight gains were 0·87,0·97 and 0·99 ±0·023 kg d−1. There were no significant interactions between silage type and the supplement offered. It is concluded that silage fermentation and metabolizable energy contents were similar for the untreated and inoculant‐treated silages but that silage dry matter intake and liveweight gain were significantly greater for the inoculant‐treated than for the untreated silage. Further work is needed to elucidate the mode of action of this type of silage additive.