Dietary supplementation of ruminant diets with an Aspergillus oryzae α-amylase

Abstract

Research in the area of dietary enzyme supplements for ruminant diets has primarily focused on fibrolytic enzymes, while activities involved in the process of starch digestion have been largely ignored. Since starch represents a major component in diets fed to highly productive cattle, the use of enzymatic dietary supplements to manipulate starch digestion in the rumen may allow improved productivity. This review discusses current information on dietary supplementation of calf, dairy and beef cattle diets with an Aspergillus oryzae extract containing α-amylase activity. During starch hydrolysis, α-amylase randomly cleaves starch polymers to low molecular weight oligosaccharides and eventually produces maltotriose and maltose from amylose and α-limit dextrins, maltose and glucose from amylopectin. Through its hydrolytic action, supplemental α-amylase hypothetically increases the availability of starch hydrolysis products in the rumen consequently altering the ruminal fermentation process. Data from studies employing lactating dairy cows, steers or rumen-simulating continuous cultures suggest that supplemental α-amylase did not increase ruminal starch digestion but consistently increased butyrate and reduced propionate molar proportions in the rumen. The increase in ruminal butyrate was also reflected in higher blood β-hydroxybutyrate concentrations in both transition and lactating dairy cows. In addition, supplemental α-amylase enhanced ruminal epithelium growth in dairy calves, a tissue that preferentially uses butyrate as an energy source. Experiments with pure cultures of ruminal bacteria showed that supplemental α-amylase supported rapid growth of bacteria that cannot grow, or grow slowly, on starch such as Butyrivibrio fibrisolvens D1, Selenomonas ruminantium GA192 or Megasphaera elsdenii T81. In contrast, bacteria that grow rapidly on starch, such as Streptococcus bovis S1 or Butyrivibrio fibrisolvens 49, did not benefit from α-amylase supplementation. Animal performance studies showed higher weight gain, and longissimus muscle area, in finishing beef cattle fed supplemental α-amylase. Weight gain improvements were primarily mediated through increased dry matter intake, which may be a consequence of reduced ruminal propionate molar proportions reported in other studies. In lactating dairy cattle, supplemental α-amylase increased milk yield, reduced milk fat proportion without reducing milk fat yield and tended to improve milk protein yield when data from 45 commercial herds (approximately 8150 cows) were examined. Currently available data on effects of the Aspergillus oryzae α-amylase described here suggest that this enzyme supplement may improve animal productivity by modifying ruminal starch digestion without necessarily increasing starch digestion in the rumen.