Effect of underfeeding on metabolism of portal-drained viscera in ewes

We investigated whether short-term underfeeding could induce adaptative mec hanisms in portal-drained viscera (PDV) that would allow nutrients to be sp ared for vital functions in adult ewes. Six ewes (three of them fitted with catheters in the mesenteric artery and portal and mesenteric veins) were f ed, in a double 3 x 3 Latin square design (2 weeks per experimental period) , a regrowth of natural grassland hay at 143 (high; H), 88 (medium; M) and 51 (low; L) % of their energy maintenance requirements. The digestibility o f the diet was measured in all six ewes and the net portal fluxes of nutrie nts in the three catheterized ewes. The organic matter content and N digest ibility of the diet were not affected by underfeeding. Urinary and faecal N losses and N balance were linearly related to feed intake. Arterial concen tration of acetate was linearly related to feed intake. Arterial concentrat ions of the other volatile fatty acids, 3-hydroxybutyrate, lactate, glucose , NH3, urea and total amino acids were not affected by underfeeding. Arteri al concentration of non-esterified fatty acids (NEFA) increased with underf eeding. The portal net release of all volatile fatty acids, 3-hydroxybutyra te and NH3 were linearly related to intake. The portal net flux of both ess ential and non-essential amino acids, and thus total amino acids, remained unchanged between levels H and M, and decreased between levels M and L. A s ignificant net uptake for glycine and total non-essential amino acids occur red at level L,. The portal net uptake of glucose, urea, glutamate and glut amine, and the portal net release of lactate and NEFA were not affected by underfeeding. Summation of portal energy fluxes indicated that 51 % of the metabolizable energy intake was recovered in the portal blood with the thre e levels of intake. In conclusion, no quantitative adaptation to spare ener gy, in terms of percentage of intake, occurred in PDV of short-term underfe d ruminants, but the pattern of absorption of energetic nutrients was modif ied.