Effects of fresh forage inclusion in diet of high performance dairy cows on milk production and composition

Introduction Whole-crop maize silages are often the major forage fi ber sources in dairy cow diets, as well as, they are prone to aerobic deterioration with decrease of their nutritive value. Bacterial inoculants containing Lactobacillus buchneri, a heterofermentative lactic acid bacterium (LAB), have been developed and its effect, as an additive that could improve the aerobic stability of silages, has been extensively studied (Kleinschmit and Kung 2006). Recently, dual-purpose inoculants containing homofermentative and heterofermentative LAB have been developed to overcome the limitations of inoculants containing either type of bacteria alone and positive effects on the aerobic stability of maize silage have been reported (Kang et al. 2009; Tabacco et al. 2011). The aims of this research were to study the effects of a commercial inoculant containing a strain of L. buchneri that produces ferulate-esterase in combination with a homofermentative LAB on aerobic stability, microbial status, dry matter (DM) losses, fermentation products and nutritional characteristics of maize silages ensiled at different DM contents. Material and methods The experiment was performed at the experimental farm of the University of Turin in the western Po plain, northern Italy (44°50´ N, 7°40´ E, altitude 232 m above sea level, annual mean temperature 11.7°C, and annual average rainfall 739 mm). Four whole-crop maize crops (trial I, II, III, and IV), differing in stage of maturity and in DM content at harvest, were chopped with a precision forage harvester, untreated or treated with inoculant (11CFT inoculant, Pioneer Hi-Bred International, Des Moines, IA), and ensiled in 20 l laboratory silos, with three replicates for each treatment. The inoculant was applied at the recommended rate of 1 g Mg-1 of fresh forage to achieve a fi nal application rate of 1×104 cfu g-1 of L. casei strain LC32909 and 1.0×105 cfu g-1 of L. buchneri strain LN40177. All silos were weighed and ensiled for about 10 months. After conservation, silos were weighted, opened and aerobic stability, pH, mould and yeast counts, fermentation products and nutritional characteristics of silages were determined. Aerobic stability was determined by monitoring temperature increases due to microbial activity and it was defi ned as the number of hours the silage remained stable before rising more than 2°C above room temperature. All silages were analyzed for NDF (aNDF), and in vitro NDF digestibility after 48 hours (NDFD).The signifi cance of the inoculation effect was tested separately for the four trials and between-treatment comparisons were made using the unpaired Student’s t-test. Aerobic stability and yeast count from the four trials were regressed on the content of acetic acid as independent variable. A regression analysis was performed to select the best regression model at P < 0.05. Results and discussion Whole-crop silage DM contents encompassed all the full range in silage DM content (from 250 to 450 g kg-1 DM) that can occur on farm (Table 1). The application of the bacterial inoculant containing L. buchneri resulted in silages with lower concentration of lactic acid, higher concentrations of acetic acid, lower lactic-to-acetic acid ratio, higher aerobic stability and higher weight losses in three out of four trials. In treated silages of trials I, II, III yeast counts were always under the detection level. No effect of inoculation was observed in trial IV characterized by the highest DM content at ensiling. When all the data were analyzed together it was observed that the effect of L. buchneri decreased with increasing DM content of the crop at ensiling and it was negligible at the highest DM content of 440 g kg-1. When the yeast counts at silo opening were related to the acetic acid concentrations, it was noted that yeast fell under the detection limit when the acetic acid content exceeded 25 g kg-1 DM (Figure 1) and, consequently, aerobic stability of silage increased to over 200 hours. The strong relationships between the content of acetic acid and the yeast count and between the content of acetic acid the aerobic stability of silages is in agreement with the results of Schmidt and Kung (2010). No effects were observed on NDF-D of silages, measured after 48 hours of incubation, in any of the four trials. These results partially agree with fi ndings of Kang et al. (2009), who reported an increase in NDF-D at 48 h only in one out of two trials on maize silage. Conclusions Inoculation with L. buchneri that produces ferulate-esterase increased aerobic stability in three out of four trials, by shifting the fermentation of silage towards an heterolactic pathway (i.e. increased acetic acid content that decreased yeast count), but did not affect NDF digestibility of silage at opening. Furthermore, there were some evidences that the effect of inoculation decreased with increasing DM content at ensiling and that it was ineffective at DM contents higher than 400 g kg-1