Utilization of 15N-Diammonium Phosphate by Ruminants to Produce Milk and Meat Proteins

The authors investigated the alimentary role of diammonium phosphate (DAP) in ruminants. For this study DAP labelled with 15N was used; analysis of the 15N atomic per cent excess was made with an Italelettronica mass spectrophotometer (model SP 21 F) and the amino acid determination by a Beckman-Spinco amino acid analyser (model 120B) fitted with a preparative column. For the experiment 7 g of DAP at 15 and 20 at. % excess 15N were administered once to mature lactating and non-lactating sheep, respectively. The measurement of 15N in the protein and isolated amino acids of milk and meat showed: (1) The milk protein produced in the first 24 h contained the highest atomic per cent excess of 15SN, 0.093; (2) That the supplemental 15N was found in all the amino acids of milk proteins except tryptophane. The atomic per cent excess of 15N was observed to vary between the various amino acids. These results confirmed previous observations on bacterial protein synthesized from DAP. (3) Muscle protein 15N maximized on the third day after administration of the 15N-DAP, with an atomic per cent excess of 0.040; (4) The atomic per cent excess of 15N in the individual amino acids of muscle protein is significant in only two amino' acids, serine and cystine; and (5) That after 8 d of adaptation there are no traces of DAP in milk or meat proteins, urine or faeces. The authors conclude that the ruminant, after a period of adaptation and through the mediation of ruminant microorganisms, is able to use the nitrogen of diammonium phosphate for the synthesis of milk and meat proteins. (author)