CONTINUOUS PROFILES AND WITHIN-DAY VARIATIONS OF METABOLITES AND HORMONES IN COWS FED DIETS VARYING IN ALIMENTARY SUPPLIES BEFORE SHORT-TERM FEED DEPRIVATION

We investigated continuous profiles and within-day variations of some metabolites and hormones in four nonpregnant, nonlactating cows fed ha y-based diets in two equal meals. Diets supplied either too much or to o little N (approximately 1.3 or .8 times the maintenance requirements ) and NE1 (approximately 1.2 or .8 times). Continuous collection of ru minal liquor, blood, and urine samples was performed for 42 consecutiv e hours, the last 16 h covering a period without feed. For twice-daily feeding, nitrogenous and energetic underfeeding decreased average rum inal propionate and the insulin:growth hormone ratio. However, only th e energetic underfeeding increased plasma S-methylhistidine and urinar y excretion of 3-methylhistidine, and decreased body weight and rumina l acetate, butyrate, and total VFA. Conversely, only the nitrogenous u nderfeeding decreased glycemia. Whatever the dietary level, the 42-h p atterns of metabolites and hormones were mainly affected by the time f rom the last meal. An energy deficit progressively took place during f eed deprivation and the nocturnal interprandial period but not during the diurnal interprandial period. During the feed deprivation and noct urnal periods, glycemia was maintained despite a shortage in ruminal p ropionate. We conclude that in twice-daily fed cattle 1) the dietary s upply of energy is the main trigger for an energy deficit and the subs equent muscle protein mobilization; 2) the nocturnal interprandial per iod may be considered as short-term feed deprivation; 3) the diurnal p atterns of metabolites and hormones are not affected by the nitrogenou s and(or) energetic supplies of the diet.