In vitro evaluation of fibrolytic enzymes as additives for maize ( Zea mays L.) silage : I. Effects of ensiling temperature, enzyme source and addition level

Abstract

A series of experiments was completed to investigate the impact of addition of enzymes at ensiling on in vitro rumen degradation of maize silage. Two commercial products, Depol 40 (D, Biocatalysts Ltd., Pontypridd, UK) and Liquicell 2500 (L, Specialty Enzymes and Biochemicals, Fresno, CA, USA), were used. In experiment 1, the pH optima over a pH range 4.0–6.8 and the stability of D and L under changing pH (4.0, 5.6, 6.8) and temperature (15 and 39 °C) conditions were determined. In experiment 2, D and L were applied at three levels to whole crop maize at ensiling, using triplicate 0.5 kg capacity laboratory minisilos. A completely randomized design with a factorial arrangement of treatments was used. One set of treatments was stored at room temperature, whereas another set was stored at 40 °C during the first 3 weeks of fermentation, and then stored at room temperature. Silages were opened after 120 days. Results from experiment 1 indicated that the xylanase activity of both products showed an optimal pH of about 5.6, but the response differed according to the enzyme, whereas the endoglucanase activity was inversely related to pH. Both products retained at least 70% of their xylanase activity after 48 h incubation at 15 or 39 °C. In experiment 2, enzymes reduced ( P<0.05) silage pH, regardless of storage temperature and enzyme level. Depol 40 reduced ( P<0.05) the starch contents of the silages, due to its high α-amylase activity. This effect was more noticeable in the silages stored at room temperature. Addition of L reduced ( P<0.05) neutral detergent fiber (NDF) and acid detergent fiber (ADF) contents. In vitro rumen degradation, assessed using the Reading Pressure Technique (RPT), showed that L increased ( P<0.05) the initial 6 h gas production (GP) and organic matter degradability (OMD), but did not affect ( P>0.05) the final extent of OMD, indicating that this preparation acted on the rumen degradable material. In contrast, silages treated with D had reduced ( P<0.05) rates of gas production and OMD. These enzymes, regardless of ensiling temperature, can be effective in improving the nutritive quality of maize silage when applied at ensiling. However, the biochemical properties of enzymes (i.e., enzymic activities, optimum pH) may have a crucial role in dictating the nature of the responses.