RUMEN ESCAPE AND APPARENT DEGRADATION OF AMINO-ACIDS AFTER INDIVIDUALINTRARUMINAL ADMINISTRATION TO COWS

Apparent rumen degradation and escape of 18 amino acids (AA) after ind ividual administration intraruminally were studied using two nonpregna nt, nonlactating, rumen-cannulated cows fed a ration containing hay an d concentrate twice daily. The pulse-dosages of AA were 75, 150, 300, and 600 mmol. Polyethylene glycol was used as the liquid marker. Rates of apparent degradation during the first 60 min (initial degradation) varied markedly among the AA; rates were highest for Ser, Asn, Glu, a nd Gln and lowest for Tyr, Val, Arg, and His. At the 75-mmol dosage, w hich corresponded to an initial substrate concentration of about 1 mM of rumen fluid, initial degradation varied between 95 and 40% of the d osage, depending on the AA. Rates, expressed as percentages of the dos age, decreased as dosages increased. During the first 8 h after admini stration, escape of the AA increased from a mean of 9% at the lowest d osage to a mean of 21% at the highest dosage. At the highest dosage, M et caused a net increase in the concentration of 11 of the other AA in rumen fluid. Twelve of the AA administered caused a net increase in t he concentration of Ala in rumen fluid. Methionine and Lys are among t he AA considered to be limiting to milk yield. These AA showed relativ ely high rumen escape values and may be useful as feed supplements eve n in an unprotected form.