Circadian changes in net nutrient fluxes across the portal-drained viscera, the liver, and the hindquarters in preruminant calves.

The objective of this study was to describe in preruminant calves the circadian patterns in net nutrient fluxes across the portal-drained viscera, the liver, and the hindquarters and to relate them to previously published variations in tissue energy expenditure. In vivo arterio-venous techniques were used, and animals were fed a conventional milk replacer. In the portal-drained viscera, net glucose absorption occurred 1 to 5 h postprandially with some lactate release. Arterial plasma non-esterified fatty acid (NEFA) concentrations decreased subsequently, as well as net NEFA uptake by the portal-drained viscera. Triglyceride absorption that occurred 1 as well as 7 or 8 h postprandially did not take place via the portal vein. Changes in energy expenditure of the portal-drained viscera did not correlate with changes in net nutrient fluxes. In the liver, the maximum contribution of lactate to hepatic glucose production was 20%. The NEFA and triglycerides were taken up by the liver, whereas urea was released. Only increases in NEFA uptake could partly explain the postprandial rise in hepatic energy expenditure. In the hindquarters, up to 48% of the glucose taken up could be converted into lactate; the remaining balance was possibly oxidized, thereby contributing as much as 33% to energy expenditure. No hourly patterns were noted in net nutrient fluxes through hindquarters. In conclusion, in preruminants, contribution of nutrients to oxidation differed from that noted in ruminants and seemed to vary with nutrient absorption and availability patterns, especially in the portal-drained viscera.

Digesta flows in sheep fed poor-quality hay supplemented with urea and carbohydrates.

Two metabolism trials were conducted with 12 yearling crossbred wethers per trial (34 and 38 kg for trials 1 and 2, respectively). The wethers, equipped with ruminal, abomasal and ileal cannulae, were randomly allotted for each trial to the following treatments: 1) hay alone or hay supplemented with 2) .9% urea, 3) 1% urea and 6.5% molasses or 4) 1% urea and 5.2% corn. Two digestive flow markers were used: Cr2O3 powder and Co-ethylenediaminetetraacetic acid (Co-EDTA). Urea and Co-EDTA were infused continuously into the rumen via cannula. Daily dry matter (DM) intake averaged 517 g. Urea supplementation improved N retention (P less than .01). Apparent digestibility of DM, acid detergent fiber (ADF) and energy was not affected by treatment. Urea and carbohydrate supplementation increased ruminal propionic acid molar proportions (P less than .05). Apparent ruminal DM digestion accounted for 41% of the total DM degraded, whereas 77.4% of the digestible ADF was degraded in the rumen. Urea supplementation increased ADF digestion in the large intestine (P less than .01). Urea and carbohydrate supplementation resulted in a stepwise increase in N flowing with the liquid phase at the abomasum. Mean retention times of the solid and liquid phases of digestive contents were similar across treatments. Overall, benefits of supplementation of poor-quality fescue hay diets by small amounts of urea and readily available carbohydrates remain questionable for sheep fed at a fixed level of intake below maintenance.

Circadian changes in energy expenditure in the preruminant calf: whole animal and tissue level.

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.

Energy cost of standing and circadian changes in energy expenditure in the preruminant calf.

An experiment was conducted with four preruminant calves to measure the energy cost and the diurnal pattern of physical activity in tethered, fed calves and to determine whether differences in activity could interfere with the interpretation of circadian changes in heat production. Measurements were carried out in large respiration chambers (3,650 L of inner volume), and a computation method was presented that allowed the calculation of the energy cost of standing for each standing period. This cost averaged 449 cal.kg BW-1.h-1 (SE = 41.6, n = 4). It represented a 23 to 27% increase in heat production above that measured in the lying state. This estimate and its standard error were lower than values obtained by regression (2,131 cal.kg BW-1.h-1, SE = 862.2, n = 8). The energy cost of standing was highest after meal times and lowest at night. These variations could reflect the nonuniform activity patterns of calves while standing. The time spent standing per hour showed the same variations during the day as the energy cost of standing. Noteworthy, the elevated energy expenditure measured in the 1st h after the morning meal was due to activity cost rather than to meal thermogenesis. Standardization of diurnal heat production profiles to a given activity pattern thus seemed to be necessary.

Maintenance requirements in metabolizable energy of adult, nonpregnant, nonlactating Charolais cows.

The objective of this study was to determine the maintenance requirements in metabolizable energy (MEm) of adult, nonlactating, nonpregnant Charolais cows. A feeding trial was conducted using 12 cows fed at one of two feeding levels (75 [L] and 113 [H] kcal of ME.kg BW-.75.d-1) 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 (HP) 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 MEm varied from 112 to 105 kcal.kg BW-.75.d-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 MEm.

[Adaptation of energy metabolism in under-fed ruminants. Quantification in the whole animal and body tissues]. / Adaptation du métabolisme énergétique des ruminants à la sous-alimentation. Quantification au niveau de l'animal entier et de tissus corporels.

Ruminants respond to underfeeding by a progressive adaptation until a new equilibrium between dietary supply and requirements is reached. The resulting drop in maintenance energy requirements originates from a decrease in basal metabolism that depends on the level and duration of undernutrition. These modifications are not totally accounted for by changes in live weight but might be explained by differential changes in individual tissue weight and metabolism. Tissues contribute to whole animal expenditure in a disproportionate manner relative to their weight. Thus digestive tract, liver and muscle masses contribute 5-11, 1-2.5 and 35-50% to live weight but about 16-29, 17-31 and about 16% to whole animal energy expenditure, respectively, because of differences in tissue metabolic activity. Underfeeding results in a decrease in the contribution of viscera to energy expenditure, whereas results on muscle mass are scarce. These changes in contribution are due to changes in tissue mass, nutrient supply (blood flow) and/or in metabolic activity.

[Methods of analysis relating to blood flow measurement of the viscera and aorta in sheep]. / Méthodes d'exploitation de données concernant les débits sanguins mesurés au niveau des viscères et du train-arrière chez la brebis.

Two methods of analysis of blood flow data are presented. They are aimed at reducing: 1) the methodological variability associated with splanchnic blood flows measured by dilution (PAH) and 2) the variability of aortic blood flows measured ultrasonically associated with physical activity. Six multicatheterized ewes were used; they were first fed at maintenance and then at half-maintenance. Observed splanchnic blood flows were very variable when PAH was infused in mesenteric vein only (average CV = 17%). Variability was first reduced by a PAH infusion via both a mesenteric and a ruminal vein (CV = 11%), second by rigorous corrections on instantaneous blood flow data (CV = 13.5%), or by a combination of both (CV = 9.5%). Corrections did not modify the conclusions of the analysis of variance concerning the treatment effect, but reduced the residual variance and eliminated the negative hepatic artery blood flow values. At the hindquarters level, corrections allowed us to approach the aortic blood flows of animals in a similar 'quietly standing' state. They decreased the daily variability (from 22 to 8%) and enabled the detection of a treatment effect, which was not shown by observed data.

Adaptation of energy metabolism to undernutrition in ewes. Contribution of portal-drained viscera, liver and hindquarters.

Adaptation of energy metabolism to undernutrition and to the duration of undernutrition was studied in adult, non-pregnant, non-lactating ewes at the whole-animal, portal-drained viscera, liver and hindquarters levels. Arterio-venous and indirect calorimetry techniques were used. Animals were successively fed at 1 times (3 weeks) and at 0.5 times (7 weeks) their metabolizable energy requirements 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%. In the portal-drained viscera and liver, O2 extraction rates decreased, leading to 34 and 38% drops in O2 consumption with underfeeding respectively. In the hindquarters, O2 extraction rate increased, partly counterbalancing the drop in blood flow. Thus O2 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, 32 and 5% respectively of the drop in whole-animal O2 consumption with underfeeding. At the end of the 0.5 x MEm period, in vivo metabolic rates averaged 1.65, 4.89 and 0.38 mmol O2 consumed/d per g fresh weight of adipose-tissue-free portal-drained viscera, liver and boneless hindquarters respectively. Undernutrition imposed a much greater nutritional challenge to splanchnic tissues than to hindquarters. The former reduced their energy expenditure whereas hindquarters metabolism adapted by counteracting the slight drop in nutrient supply.

[Measure of splanchnic blood flow by marker dilution: comparison of 4 methods of para-aminohippuric acid determination]. / Mesure des débits splanchniques par dilution de marqueur: comparaison de quatre méthodes de dosage de l'acide para-amino-hippurique.

The objective of this study was to determine the influence of the analytical method of para aminohippuric acid (PAH) on splanchnic blood flows, as measured by a dye dilution method in ovines. Four different analytical methods of PAH were compared. They differed in the pretreatment of the samples and in the presence or absence of a deacetylation step to account for the partial acetylation of PAH in the liver (13%). The optimum conditions of deacetylation were defined as 60 min of incubation at 90 degrees C in presence of HCl (5N). The four analytical methods were checked to be linear (from 0 to 35 mg/L), repeatable (CV = 0.70%) and reproducible (CV = 2.1%). It appeared necessary to prepare the standards in the same matrix as that of the samples. The choice of the analytical method was responsible for differences in PAH concentrations and in the absolute values for portal and hepatic blood flows, which could reach 21%. The presence of a deacetylation step with HCl significantly reduced the contribution of the hepatic artery to the total hepatic blood flow (from 24 to 10%). Consequently, this study showed that the nature of the analytical method chosen can highly influence the measurements of splanchnic nutrient fluxes. The recommended analytical method is the one which includes a deacetylation step.

The effect of fishmeal supplementation of a straw-based diet on growth and calorimetric efficiency of growth in heifers.

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 (F0, 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 (W0.75) for the LFO diet and 74.7 g/d per kg W0.75 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 0.69 and those for acid-detergent fibre digestibility were 0.60, 0.63, 0.66, 0.58, 0.60 and 0.65 for diets LF0, LF1, LF2, HF0, HF1 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 LF0, LF1 and LF2 diets and 468, 651 and 710 g/d for the HF0, 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 W0.75 for diets LF0, LF1, LF2, HF0, HF1 and HF2 respectively, but no definite evidence was obtained that dietary supplementation with fishmeal modified the efficiency of utilization of metabolizable energy for growth.

Nutrient supply and growth of cattle offered straw-based diets.

An experiment was conducted using steers cannulated at the rumen, duodenum and ileum to study the effects of increasing the levels of barley and fishmeal in straw-based diets. Diets A, B, C and D contained ammonia-treated straw, barley and fishmeal in the ratios, 67:33:0, 66:23:11, 53:47:0 and 52:36:12 (by weight) and were offered in daily amounts of 3.9, 3.9, 4.8 and 4.8 kg dry matter. The effects of barley were attributable to increased intakes of digestible organic matter and consequently to increased flows of microbial matter to the duodenum. There were no modifications in the balance of energy to nitrogen-yielding nutrients available for absorption. Introducing fishmeal into diets improved digestibility of cellulose and xylose by up to 6.7 and 4.7% respectively, and shifted digestion towards the large intestine. Second, it increased amino acid N supply to the small intestine which averaged 52.2, 63.2, 68.8 and 84.0 g/d with diets A, B, C and D. Some changes were also noted in the balance of amino acids absorbed. Consequently, the contribution of amino acids to metabolizable energy intake increased with the proportion of fishmeal in diets (0.17, 0.20, 0.18 and 0.21 for diets A, B, C and D). Growth rates measured in heifers amounted to 259, 431, 522 and 615 g/d for diets A, B, C and D. They appeared to be related to intestinal amino acid supply.