CONTINUOUS PROFILES OF RUMINAL AMMONIA AND PLASMA UREA IN DRY FRIESIAN COWS ON HAY-BASED RATIONS

In order to study the simultaneous changes of ruminal ammonia and plas ma urea during periods without any feed intake, automated sampling pro cedures were performed on 17 fed and short-term fasted Friesian dry co ws. Hay-based rations with different energy and/or nitrogen supplies w ere fed in two equal meals daily (0615-1530 h). The pattern of metabol ites profiles was apparently nor influenced by dietary supplies. Two d aily postprandial ammonia peaks, higher in the morning than in the aft ernoon, occurred systematically and were linked by a nocturnal accumul ation of ammonia. Plasma urea concentration systematically increased o vernight, following a 24-h sinusoid-like pattern with minimum and maxi mum daily data occurring around 0000 and 0800 h, respectively. Continu ous metabolites changes were overall similar during short-term fasting and nocturnal interprandial periods. Plasma urea profiles are suggest ed as being influenced by a body-protein mobilization occurring during periods without any feed intake. During such periods, ruminal ammonia accumulation was suggested to result mainly from the urea transfer fr om blood into the rumen.