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

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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,...

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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.

ABSTRACT:The objective of this study was to determine the maintenance requirements in metabolizable energy (ME m) of adult, nonlactating, nonpregnant Charolais cows. A feeding trial was conducted using 12 cows fed at one of two feeding levels (75 for 116 d. Body composition was estimated from subcutaneous adipocyte diameter. Body weight changes averaged -468 and +46 g/d, respectively. Diet DM digestibility averaged .496. The L cows spent less time eating and ruminating but had other behavioral characteristics similar to those of H cows. Estimates of MEm were calculated from BW or body composition changes and amounted to 109 and 124 kcal of ME.kg BW-.75.d-1, respectively. Heat production ( H P ) was then measured over 67 d in a second trial on two L and two H cows from the feeding trial and planes of feeding were switched after 14 d. Estimates of ME, varied from 112 to 105 kcal-kg BW-.75&1. Within animal, day-to-day variations in heat production were high (4.6% on average) and prevented the detection of any precise changes of HP with time on treatment. None of the trials showed any significant effect of level of feeding on ME,.

A study was conducted using four preruminant calves to determine the contribution of portal-drained viscera, liver, and hindquarters to circadian changes in total energy expenditure, after removing variations due to behavioral patterns. Indirect calorimetry and in vivo arterio-venous techniques were used. Standing time was longer (P < .01) after the meals and shorter (P < .01) at night. These variations were associated with higher (P < .01) energy cost of standing immediately after the meals and lower (P < .01) ones at night. When these behavioral effects were removed, total energy expenditure of lying calves was shown to be stable between the morning and evening meal, to increase by 11.5% and remained elevated during the 6 h after the evening meal, and to reach the lowest values at night. Portal-drained viscera and liver contributed 32.8 to 53.7% and 29.1 to 32.2%, respectively, to the circadian variations calculated for calves that were always standing. Changes in splanchnic tissue energy expenditure resulted from combined modifications in blood flow and O2 extraction rate. The contribution of hindquarters could not be clearly established. Overall, portal-drained viscera, liver, and hindquarters contributed 17.2, 12.8, and 18.0%, respectively, to total energy expenditure of standing calves. Their respective in vivo metabolic activities averaged 1.08, 2.10, and .25 mumol of O2 consumed.min-1.g-1 of fresh tissue.

Thirty-two 160 kg dairy heifers were used to measure the effects of increasing dietary protein content on growth and heat production. A basal diet containing (g/kg) 550 sodium hydroxide-treated straw, 220 barley, 220 sugarbeet pulp and 10 urea was offered with 0,76 and 152 g fishmeal/kg dry matter of the basal diet (FO, F1 and F2 levels respectively). The three diets were each given at two levels of feeding (low, L; high, H): 57.6 g/d per kg metabolic body-weight (Wo7') for the LFO diet and 747 g/d per kg Wo7' for the HFO diet. Apparent digestibility of the diets increased in response to the addition of fishmeal. Mean dry matter digestibility values were 0.67, 0.67, 0.69, 0.66, 0.68 and 069 and those for acid-detergent fibre digestibility were 0.60,0.63,066,0.58,060 and 0.65 for diets LFO, LF1, LF2, HFO, HFl and HF2 respectively. Nitrogen retention increased in response to both fishmeal and feeding level. Live-weight gains were 170, 296,434 g/d for the LFO, LFl and LF2 diets and 468,651 and 710 g/d for the HFO, HF1 and HF2 diets respectively. There were significant effects of increasing the plane of feeding and the level of fishmeal in the diet on live-weight gain. Dietary effects on live-weight gains were accompanied by increases in mean energy retention of 23,45,82,94,160 and 152 kJ/d per kg WO" for diets LFO, LFl, LF2, HFO, H F l and HF2 respectively, but no definite evidence was obtained that dietary supplementation with fishmeal modified the efficiency of utilization of metabolizable energy for growth.