Effects of applying a bacterial inoculant to silage immediately before feeding on silage intake, digestibility, degradability and rumen volatile fatty acid concentrations in growing beef cattle

In an experiment, involving twelve male cattle (initially 235 kg live weight), the effects of applying lactic acid bacteria [Lactobacillus plantarum; 10(9) colony-forming units (g fresh silage)(-1)] to grass silage, immediately prior to that silage being fed, on dry-matter (DM) intake of the silage, degradability of nitrogen (N) and fibre in the rumen, total tract digestibility and composition of rumen fluid in the animals were examined. A grass silage, which had been made from the primary growth of a predominantly perennial ryegrass sward, was offered as the sole diet. The inoculant was applied to the silage at the rate of 2 g of freeze-dried powder reconstituted in 12 ml of water (kg fresh silage)(-1) immediately prior to that silage being fed and an equivalent amount of water was applied to the silage in the control treatment. The two diets were compared in a change-over design. The silage was well preserved, having a pH and concentrations of ammonia N and butyrate of 3.72, 74 g (kg total N)(-1) and 0.11 g (kg DM)(-1) respectively. Application of the inoculant significantly increased true protein, acid-insoluble N and water-soluble carbohydrate concentrations (P<0.001) in the diet. Silage DM intake was not significantly increased (P = 0.072) by this of inoculant treatment, which had no significant effect (P>0.05) on rumen degradability or total tract digestibility of DM, N, neutral detergent fibre or modified acid detergent fibre. Rumen pH, ammonia concentration or the molar proportions of volatile fatty acids were not altered (P>0.05) by inoculant treatment. It is concluded that application of the inoculant to the silage prior to silage being fed did not significantly affect silage DM intake, total tract digestibility, or degradability or fermentation in the rumen of cattle offered grass silage as the sole diet. It is also concluded that the results of this experiment provide no evidence that the mode of action of L. plantarum, applied as an additive to grass at ensiling in previous studies, is through 'direct' effects in the rumen.