Grains in ruminant feeding and potentials to enhance their nutritive and health value by chemical processing

Abstract

Cereal grains have long been an important component of the diet in ruminants. The primary aim of feeding grains to ruminants is that their high starch content enables high energy density of ruminant’s diets to support production. Grains differ among them in their starch content and ruminal effective degradability. The digestibility and utilisation of starch is instrumental for the nutritive value of grains in ruminants. Therefore, attempts were initially made to enhance starch digestibility and utilisation using mechanical or thermal processing methods. However, extensive grain processing also accelerates ruminal starch degradation, enhancing the risk of rumen fermentation disorders. Research has shown that treatment of whole grains with alkaline substances like sodium hydroxide increases degradability of the seed coat and subsequently whole grain degradation within the rumen, saving the costs for grinding. The same treatment has also been shown to slower the rate of starch degradation in the rumen and improve fibre digestibility with potential beneficial effects on intake and production. Furthermore, treatment of milled grains with formaldehyde has been used to retard the rate of starch and protein degradation in the rumen of cereal starch and protein. Decreasing ruminal starch degradation and enhancing ruminally undegraded starch in grains is important to lower the risk of rumen fermentation disorders when grains are fed in large amounts. A major drawback of sodium hydroxide and formaldehyde are however the high corrosiveness and health risks for the users. Ammonia has also been used to lessen ruminal nutrient degradation of grains including starch and protein degradation. Furthermore, this treatment elicits positive effects in enhancing the crude protein content of the treated grain for ruminants, especially of maize. Moreover, ammonia has shown promising effects for preservation of whole high moisture grains. Increasing research efforts have also been done to identify new chemical grain processing techniques, mainly by using mild organic acids. Besides affecting the rate and site of starch digestion, the use of lactic acid has shown to improve the utilisation of organically bound phosporus (P). Indeed, in addition to starch and protein grains also are important sources of minerals, especially of P, in ruminant diets. Increased availability of this key mineral for rumen microbes, and the host metabolism by chemical treatments enhances the nutritive value of grains and saves inorganic P sources. The aim of this review is to update the current knowledge regarding the effects of different chemical processing techniques of cereal grains in ruminant nutrition related to the effects on nutritive and health value of grains.