Estimation of in vitro degradation of dietary proteins in ruminants by using enzymes

Extract

Protein degradation in the rumen determines the supply of dietary nitrogen (N) to microbes and undegraded amino acids for direct absorption. The current systems of feeding ruminants identify rumen degradable protein (RDP) from undegraded protein (UDP) which is digestible post ruminally (Agricultural and Food Research Council (AFRC), 1992; Huntington and Givens 1995). The in sacco method has been useful to estimate RDP, UDP and rate of degradation of proteins in ruminants. However, its use is constrained by the fact that it requires surgically modified animals, is laborious, inconsistent and does not differentiate between proteins that disappear from the bag or which are digested by microbes. It is therefore important to develop rapid, robust and reproducible alternatives (in vitro) to simulate ruminal digestion of proteins. Chaudhry (1998) has shown a potential in Streptomyces griseus protease (enzyme) to estimate ruminal digestion in vitro given its consistently high proteolytic activity with purified proteins. This study examined the validity of this enzyme to estimate degradability of food proteins.

Buffer, enzyme and foods A potassium phosphate buffer (buffer) with a pH 6-8 was used to prepare protein suspensions and a solution of the protease (P5147, SIGMA). Samples of sunflower meal (SF), maize-gluten meal (MG), distillers’ dark grains (DG) and field beans (FB) were dried and ground through 1 or 4 mm sieves for in vitro enzyme and in sacco studies respectively.