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 hay-based diets in two equal meals. Diets supplied either too much or too little N (approximately 1.3 or .8 times the maintenance requirements) and NE1 (approximately 1.2 or .8 times). Continuous collection of ruminal liquor, blood, and urine samples was performed for 42 consecutive hours, the last 16 h covering a period without feed. For twice-daily feeding, nitrogenous and energetic underfeeding decreased average ruminal propionate and the insulin:growth hormone ratio. However, only the energetic underfeeding increased plasma 3-methylhistidine and urinary excretion of 3-methylhistidine, and decreased body weight and ruminal acetate, butyrate, and total VFA. Conversely, only the nitrogenous underfeeding decreased glycemia. Whatever the dietary level, the 42-h patterns of metabolites and hormones were mainly affected by the time from the last meal. An energy deficit progressively took place during feed deprivation and the nocturnal interprandial period but not during the diurnal interprandial period. During the feed deprivation and nocturnal periods, glycemia was maintained despite a shortage in ruminal propionate. We conclude that in twice-daily fed cattle 1) the dietary supply of energy is the main trigger for an energy deficit and the subsequent muscle protein mobilization; 2) the nocturnal interprandial period may be considered as short-term feed deprivation; 3) the diurnal patterns of metabolites and hormones are not affected by the nitrogenous and(or) energetic supplies of the diet.