The nutritive value of rumen micro-organisms in ruminants

Abstract

1. Four experiments were carried out to identify and quantify the limiting amino acids (AA) in rumen microbial protein (RMP).2. A method was developed which involved first, an assessment of the efficiency of utilization of absorbed AA-nitrogen (U) of RMP, defined as the retention of AA-N from RMP absorbed from the small intestine, and second, addition of a mixture of AA similar to the absorbed AA profile in a quantity defined by the U of RMP and equal to (1 – U)/U. Third, it involved removal of each AA in turn and measurement of the resultant N retention. Using this approach it was possible to calculate both the order and extent of AA limitations in RMP.3. Apart from methionine which was found to be the most limiting AA, only lysine, arginine and histidine reduced N retention when omitted, and accordingly only these AA were limiting in RMP.4. The method is discussed in detail and the amount of supplementary AA required to utilize RMP fully is calculated.