Effect of enzyme additives on quality of alfalfa/grass silage and dairy cow performance

Abstract

First- and second-cut alfalfa/grass forage crops were wilted to approximately 40% dry matter (DM) and ensiled untreated (control) or treated with either of two enzyme additives to determine the effects on silage quality and animal performance of crops that contain different ratios of legume to grass. An alfalfa enzyme mix (Alfa) contained cellulase, amylase and glucose oxidase; a grass enzyme mix (Grass) was similar but contained no amylase. Both additives contained identical inoculants of lactobacillus. Silage was fed to mid-lactation Holstein cows at 60 d (second cut) and 120 d (first cut) postensiling using repeated Latin square designs. Silage samples and animal performance data were collected during the last 7 d of each of three 28-d feeding periods that comprised each Latin square. Colony-forming units of lactic acid bacteria, concentrations of water-soluble carbohydrate (WSC), ammonia N, acid-detergent fiber N and organic acids, pH, DM disappearance, and temperature changes during ensiling were measured to assess silage quality. Six sheep were also used in a repeated Latin square design to determine digestibility of the second-cut silages. First-cut silage, which contained about 50% timothy, and 50% alfalfa was qualitatively similar across treatments except for a lower (P < 0.05) concentration of hemicellulose in Grass-treated silage. The only effect (P < 0.05) on quality of second-cut silage, which contained about 80% alfalfa and 20% timothy, was an increase in estimated DM loss in Grass-treated silage compared with Alfa and the control. Despite the negligible effects on silage quality parameters, Grass slightly depressed (P < 0.10) the yield of fat-corrected milk in cows fed first-cut silage, and DM intake of cows fed second-cut forage was elevated slightly (P < 0.05) and fat percent was depressed (P < 0.05) by Alfa relative to the control. Consequently, although the change was small, enzyme treatment of forages may represent a means of reducing the fat percent of milk. Sheep consumed more (P < 0.05) second-cut silage treated with Alfa, and DM digestibility was higher (P = 0.09) when compared with the control. An enzyme mixture containing amylase may be marginally more effective when forage mixtures contain more alfalfa than timothy. Key words: Silage, enzymes, dairy, cow, digestibility, milk fat