In the June 1998 issue of theNew Zealand Veterinay Journal, a clinical review was published focusing on aspects of the protein nutrition of dairy cattle (Westwoodet al., 1998). The authors wrote: “Most species of rumen bacteria can use ammonia for growth, but some, particularly bacteria which ferment cell wall carbohydrates, use or have obligate requirements for amino acids and peptides (Russelet al., 1992)”.