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.

Zusammenfassung Der Verlauf der Pansenammoniak‐ und Plasmaharnstoff‐ Konzentration von trockenstehenden Friesian‐Kühen bei Fütterung mit Rationen auf Heubasis Veränderungen des Pansenammoniakgehalts und der Blutharnstoffkonzentration wurden simultan an 17 trockenstehenden Friesian‐Kühen gemessen, die gefüttert und kurzfristig gehungert waren. Die Basisration bestand aus Heu und unterschiedlicher Energie‐ und Stickstoffsupplementierung. Die Rationen wurden zweimal am Tag um 0615 und 1530 Uhr verabreicht. Die gemessenen Parameter wurden nicht durch die Futtergabe beeinflußt. Zweimal am Tag konnte post‐prandial systematisch ein Peak beobachtet werden, dabei war der Morgenpeak stets höher als der Nachmittagspeak und stand in enger Korrelation mit der nächtlichen Ammoniakkumulation. Der Plasmaharnstoffgehalt steigt über Nacht stets an. Die Kurven haben einen sinusoidalen Verlauf mit täglichen Minima und Maxima um 0000 und 0800 Uhr. Zu beobachten sind kontinuierliche Metabolitenveränderungen beim Kurzzeitfasten und nächtliche interprandiale Intervalle. Die beschriebenen Harnstoffprofile lassen sich durch den Abbau von Körperprotein während des Fastens erklären. Die Akkumulation von NH3 im Pansen entsteht wahrscheinlich durch den Rückfluß von Harnstoff aus dem Blut zum Pansen.

The aim of the study was to investigate the changes in renal function in late pregnant and early lactating Corriedale ewes. Compared with the non-productive state, plasma urea concentration was increased by 67% during pregnancy, whereas it decreased by 36% during lactation. Urine flow, urea clearance, renal plasma flow and glomerular filtration rate were significantly reduced (P<0·05) during both late pregnancy and early lactation. Filtered load of urea and the amount of urea eliminated were significantly reduced (P<0·05) only in lactating ewes. No changes were noted in the fractional excretion of urea, the filtration fraction and the urine osmolality during both late pregnancy and early lactation. It was concluded that, as in other breeds, Corriedale ewes can adapt to increased nitrogen requirements during late pregnancy, and especially during early lactation, by increasing the renal conservation of urea. Unlike other breeds, however, Corriedale ewes restrict the urine urea losses mainly by reducing renal plasma flow and glomerular filtration rate, without any modification of the tubular reabsorption of urea during both late pregnancy and early lactation.

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