Effects of inoculant treatment on ryegrass silage fermentation, digestibility, rumen fermentation, intake and performance of lactating dairy cattle

A randomized block experiment involving thirty-six lactating dairy cattle was carried out to evaluate a bacterial inoculant (Grazyme Grobac, Agritech), containing bacteria, enzymes and a rumen enhancer, as a silage additive. Herbage from the primary regrowth of predominantly perennial ryegrass swards was ensiled unwilted and precision-chopped after a 51-d growth interval on 4 and 5 August. Alternate loads of herbage were ensiled either untreated (C) or treated with formic acid at a rate of 2.65 1 (t herbage)(-1) (F) or the inoculant at a rate of 0.64 kg (t grass)(-1) (I). The treatments were harvested using the same harvester in the rotation of I, F and C treatments. Mean dry-matter (DM), water-soluble carbohydrate and nitrate nitrogen (N) concentrations and buffering capacity of the C herbages at ensiling were 198 g kg(-1), 18.2 g kg(-1), 290 mg (1 juice)(-1) and 379 mequiv. (kg DM)(-1) respectively. For silages C, F and I pH values were 3.7, 3.8 and 3.8 and ammonia N concentrations 61, 43 and 58 g (kg total N)(-1) respectively. Inoculant treatment did not alter aerobic stability of the silages, whereas formic acid treatment increased it. The silages were offered ad libitum and supplemented with 5 kg of concentrates per head daily. For treatments C, F and I silage DM intakes were 10.8, 11.2 and 10.8 (s.e. 0.33) kg d(-1), milk yields 21.3, 20.9 and 20.7 (s.e. 0.52) kg d(-1), fat concentrations 38.3, 40.3 and 37.2 (s.e. 0.83)g kg(-1) and protein concentrations 30.8, 32.6 and 32.6 (s.e. 0.49) g kg(-1) respectively. Inoculant treatment did not alter (P>0.05) the digestibility coefficients of the total diets, whereas formic acid treatment decreased DM (P<0.05), organic matter (P<0.05), neutral detergent fibre (P<0.01) and hemicellulose (P<0.01) digestibilities. Formic acid treatment altered rumen fermentation patterns, whereas inoculant treatment had no effect. It is concluded that, relative to a well-preserved untreated silage, additive treatment did not alter DM intake, milk yield or fat plus protein yield. However, both additive treatments increased milk protein concentrations and formic acid treatment increased milk fat concentration relative to the well-preserved, untreated silage.