Impact of additional protein on nitrogen retention and amino acid absorption from small intestine in mature steers fed on grass silage

Abstract

The efficiency of dietary nitrogen use on ruminants fed on forage is poor and this may be largely attributed to an asynchrony between the supply of energy and nitrogen to the rumen microbes, resulting in poor microbial protein synthesis and a low efficiency of utilisation of absorbed amino acid (AA). One of the main factors contributing to the latter is the efficiency of absorption of AA from the small intestine and it has been concluded that a value of 0.75 is appropriate across a range of diets (MacRae and Reeds, 1980). However, it is uncertain how this value may vary on grass silage diets and what effect additional rumen undegradable protein may exert. The objective of this experiment was to measure body nitrogen utilisation and AA absorption from the small intestine in steers fed on grass silage or supplemented with fishmeal.