Summary — This review focuses on the influence of intake on the availability of digestion end products, on splanchnic tissue weights and metabolic activity, and on the consequences of these changes on whole animal energy metabolism in ruminants. An increase in intake reduces diet digestibility and modifies the relative importance of the sites of digestion. Passive

No abstract

Adaptation of energy metabolism to undernutrition and to the duration of undernutrition was studied in adult, non-pregnant, non-lactating ewes at the wholeanimal, portal-drained viscera, liver and h i u a r t e r s levels. Arterbvenous and indirect calorime.try techniqua were used. Animals were successively fed at 1 times (3 weeks) and at 0-5 times (7 weeks) their metabolizable energy reQIlirements for maintenance (MEm). Portal, hepatic and hindquarters blood flows in quietly standing ewes decreased by 22, 19 and 11% respectively within the first week of undernutrition and remained at that level thereafter. Standardizing hindquarters blood flow to that in a given posture (quietly standing) reduced blood flow by 9.8 YO. In the portaldrained viscera and liver, 0, extraction rates decreased, leading to 34 and 38% drops in 0, eonsumption with Underfeeding respectively. In the bindquarters, 0, extraction rate increased, partly counterbalancing the drop in blood flow. Thus 0, consumption of hindquarters tended to decrease but the effect was not significant. All changes appeared to be completed from day 5 of underfeeding. Consequently, the portal-drained viscera, liver and carcass were responsible for 39, 32and 5 % respectively of the drop in wholeanimal 0, consumption with underfeeding. At the end of the 0.5 x MEm period, in vivo metabolic rates averaged 165,4-89 and 038 mmol0, consumed/d per g fresh weight of adipose-tissue-free portaldrained viscera, liver and boneless hindquarters respectively. Undernutrition imposed a much greater nutritional challenge to sphchnic tissues than to hindquarters.The former reduced their energy expenditure whereas hindquarters metabolism adapted by counteracting the slight drop in nutrient supply.Energy metabolism: Hindquarters: Liver: Undernutrition: Viscera Energy utilization by tissues of economic importance (e.g. muscles, mammary gland) depends partly on the partition of metabolizable energy (ME) supply among all body-tissue compartments. Feeding level may modify this partition. Changes in the plane of feeding are associated with changes in energy expenditure of splanchnic tissues (Huntington, 1990). Since the latter contribute to a substantial proportion of whole-animal energy expenditure (35-50%; Huntington, 1990), it can be questioned whether a small modification in their energy requirements might modify the partition of energy to the benefit of peripheral tissues. The effects of feeding level have mostly been studied with animals fed at levels above maintenance. It was of particular interest to test whether in a context of undernutrition the drop in energy expenditure of splanchnic tissues could be an adaptive mechanism that would contribute to muscle saving.The time-scale of the adaptation process is also important. The lag time for changes in whole-animal energy expenditure following feed restriction was shown to vary between 6 and 21 d (Clapperton & Blaxter, 1965;Wainman et al. 1972). By contrast, Shetty (1990) suggested, in a critical literature review on human starvation,...

No abstract

SUMMARYThe objectives of this study were (i) to evaluate a new surgical procedure to catheterize hepatic vessels as well as the posterior aorta and vena cava, (ii) to test a modification of a downstream dilution technique in order to measure blood flows through splanchnic tissues and hindquarters in rapid succession, and (iii) to improve the reliability of splanchnic blood flow measurements using paraamino hippuric acid (PAH). Ten adult ewes were used. The transhepatic surgical approach used proved successful; it was relatively easy to set up and a good recovery of hepatic functions was obtained. The attempt to measure splanchnic and hindquarters blood flow in rapid succession by alternating the sites of PAH infusion was unsuccessful, probably because of transient modifications in infusion rates due to different blood pressures in veins and arteries. Indeed, arterial PAH concentrations changed with infusion site. Finally, a better reproducibility of splanchnic blood flow measurements was obtained in sheep, fed every 3 h, by infusing the required amount of PAH partly via the mesenteric vein and partly via a ruminal vein.