Peculiarities of enhancing resistant starch in ruminants using chemical methods: opportunities and challenges

Abstract

High-producing ruminants are fed high amounts of cereal grains, at the expense of dietary fiber, to meet their high energy demands. Grains consist mainly of starch, which is easily degraded in the rumen by microbial glycosidases, providing energy for rapid growth of rumen microbes and short-chain fatty acids (SCFA) as the main energy source for the host. Yet, low dietary fiber contents and the rapid accumulation of SCFA lead to rumen disorders in cattle. The chemical processing of grains has become increasingly important to confer their starch resistances against rumen microbial glycosidases, hence generating ruminally resistant starch (RRS). In ruminants, unlike monogastric species, the strategy of enhancing resistant starch is useful, not only in lowering the amount of carbohydrate substrates available for digestion in the upper gut sections, but also in enhancing the net hepatic glucose supply, which can be utilized by the host more efficiently than the hepatic gluconeogenesis of SCFA. The use of chemical methods to enhance the RRS of grains and the feeding of RRS face challenges in the practice; therefore, the present article attempts to summarize the most important achievements in the chemical processing methods used to generate RRS, and review advantages and challenges of feeding RRS to ruminants.

Figure 1

Scanning electron microscope images of starch granules of “Eureka” a 2-row-winter-feed barley cultivar (A) and “Vienna” a 2-row-summer-feed barley cultivar (B) (2000×).

Figure 2

A simplified model describing the fates of ruminally resistant starch (RRS) and non-RRS (NRS) fed to cattle. The RRS is not digested in the rumen, which results in low concentrations of short-chain fatty acids (SCFA) and a higher ruminal pH. NRS is degraded in the rumen and leads to a release of SCFA, changing the proportions of acetate (C₂): propionate (C₃) and butyrate (C₄), as well as decreasing the ruminal pH (high risk of rumen acidosis). The undigested RRS is mostly degraded in the small intestine by pancreatic amylases, some portions of it can be degraded in the large intestine. The model also indicates the mechanisms of removal of SCFA (metabolism of SCFA to beta-hydroxybutyrate (BHB), acetoacetate (AcAc), and lactate) from the rumen and the absorption of glucose from the small intestine.