Abstract:
The measurement of plasma methionine concentrations with high pressure liquid chromatography (HPLC) with a protein hydrolysate column was examined as a means of evaluating the rumen protection status of DL-methionine mixes after oral administration. Plasma methionine concentrations were measured 2, 4, 6 and 8 h after 5 different mixes had been administered to the rumen of 3 sheep by stomach tube. The plasma values were compared with the pretreatment profile (1.2-16.7 �_mol/L) obtained in the test sheep, and those obtained after abomasal and subcutaneous administration. The results suggest that none of the mixes were significantly protected from bacterial degradation in the rumen. The positive control treatments of subcutaneous or abomasal administration resulted in >10-fold increases in plasma concentrations of methionine (e.g. from 28 to 414 �_mol/L). A method of administration that required the sheep to raise their heads about 30 cm to lick a molasses + methionine mix increased subsequent plasma methionine concentrations 5 times (from 44 to 267 �_mol/L). Oral administration of 2 mixes using a drench gun also resulted in increased plasma methionine in some sheep, suggesting that these procedures allowed some methionine to bypass the rumen mechanically. A follow-on wool growth experiment using methionine + molasses mixes administered either from a 'licker' 30 cm above head level or in the feedbin failed to increase either wool growth or plasma methionine. The HPLC procedure for methionine analysis proved successful for the qualitative laboratory evaluation of the rumen protection status of methionine mixes. It is concluded that this 24 h methionine test and analysis procedure can partly replace the costly and lengthy in vivo procedure of measuring responses in wool production.