For high-intensity cycle ergometer exercise, the relation between power (P) and its tolerable duration (t) has been well characterized by the hyperbolic relationship: (P-thetaF) t = W', or P = W' (1/t)+thetaF, where thetaF may be termed the 'fatigue threshold'. The curvature constant (W') reflects a constant amount of work which is postulated to be equivalent to a finite energy store that relates to the oxygen-deficit: phosphagen pool, anaerobic glycolysis and oxygen stores. Compared to thetaF, the physiological nature of W' has received little consideration. The purpose of this study was therefore to establish the parameters of the power-duration curve (thetaF and W') for subjects in normal glycogen (NG) and glycogen depleted (GD) states. Seven healthy male subjects (aged 22 to 41 years) each performed four high-intensity square-wave exercise bouts on an electrically braked cycle ergometer under two different muscular glycogen content conditions, i.e. NG and GD states. Subjects performed the following exercise on the evening before the trial day to induce the GD state. Initially, they performed a 75-min cycling exercise at 60% of VO2max. After a 5-min rest period, they subsequently repeated a 1-min cycling bout at 115% of VO2max (separated by 1-min rest periods) until the subject could no longer maintain the prescribed pedal rate for the full minute. Subjects then reported to the laboratory after an overnight fast and performed a single high-intensity exercise bout. The GD procedure was repeated four times at 1-week intervals. In the GD state, the respiratory exchange ratio (RER) (VO2/VCO2) value during a recumbent control period prior to the trial was significantly lower than that in the NG state [GD: 0.84+/-0.02, NG: 0.94+/-0.04, mean +/- SD]. There was no significant difference for thetaF between GD and NG state [NG: 197.1+/-31.9 W, GD: 190.6+/-28.2 W]. W' in contrast was significantly reduced by the GD procedure [NG: 12.83+/-2.21 kJ, GD: 10.33+/-2.41 kJ]. The present results indicate that the muscular glycogen store seems to be an important determinant of the curvature constant (W') of the power-duration curve for cycle ergometry.

SummaryThe prediction of renal energy excretion is crucial in a metabolizable energy system for horses. Phenolic acids from forage cell walls may affect renal energy losses by increasing hippuric acid excretion. Therefore, the relationships were investigated between renal energy, nitrogen (N) and hippuric acid excretion of four adult ponies (230-384 kg body weight (BW)) consuming diets based on fresh grass, grass silage, grass cobs (heat-dried, finely chopped, pressed grass), alfalfa hay, straw, extruded straw and soybean meal. Feed intake was measured; urine and faeces were quantitatively collected for three days. y = 14.4 + 30.2x 1 +20.7x 2 (r = .95; n = 30; p < .05). Renal hippuric acid excretion was highest after intake of fresh grass and lowest after intake of soybean meal. The ratio of hippuric acid to creatinine in urine and the excretion of hippuric acid per gram of dry matter intake was significantly higher for fresh grass than for all other rations. There was no relationship between aromatic amino acid intake and renal hippuric acid excretion. The results of the present study and literature data suggest that feed can be categorized into four groups with regard to the energy losses per gram CP intake: (i) protein supplements (e.g., soybean meal): 4.2-4.9 kJ/g CP intake (ii) alfalfa hay, grains, dried sugar beet pulp: 6.4 kJ/g CP intake, (iii) hay, preserved grass products, straw: 5.2-12.3 kJ/g CP intake (mean 8) and (iv) fresh grass. For group (iii) a negative relationship was observed between renal energy losses per gram of CP and the content of CP or neutral-detergent-insoluble CP in dry matter. K E Y W O R D Shippuric acid, metabolizable energy, nitrogen excretion, phenolic acids | INTRODUCTIONRenal energy losses in horses range between 7% and 12% of digestible energy (Kienzle & Zeyner, 2010). Presumably, the reason for the high renal losses is that phenolic acids of plant cell walls can be released in the digestive tract, absorbed, metabolized to hippuric acid and eventually be excreted via urine. In addition, nitrogen (N) from excess crude protein (CP) intake is excreted as urea. Thus--like in other species-a high CP intake increases renal energy excretion. The Society of Nutrition Physiology introduced a metabolizable energy (ME) system for energy evaluation of horse feed and energy requirements for horses (GfE, 2014). A subtraction of 8 kJ/g CP in the feed is made for

Hay stabilises urine pH in horses. It is unknown whether this is an effect of structure or of chemical composition. In this study, four ponies (230-384 kg body weight [BW]) were fed six different diets with either a structure or a composition similar to hay with and without acidifiers in a cross-over experimental design in amounts to maintain body weight with the following main compounds: Fresh grass (GRASS), alfalfa hay (ALF), grass cobs (COBS), grass silage (SIL), straw (STR) or extruded straw (STRe) for 2 to 10 days. Urine pH was measured in all trials, blood pH, blood base excess and bicarbonate as well as mineral balance were determined in GRASS, ALF, STR and STRe. In the trials with straw and extruded straw, urine pH decreased significantly (STR control: 7.8 ± 0.23, acidifier: 5.2 ± 0.38) when acidifiers were added, whereas in all other diets that were based on fresh or preserved green fodder, pH did not decrease below 7. Blood pH was similarly affected by diet and acidifiers. Acidifiers had little effect on the pre-prandial blood pH, only in diet STR there was a significant reduction in relation to control. Post-prandial blood pH was significantly reduced by acidifiers in all diets. Blood bicarbonate and base excess showed corresponding effects. Faecal and renal mineral excretion and apparent mineral digestibility were not systematically affected by diet or acidifiers except for chloride. Chloride added as inorganic chloride salt had an even better apparent digestibility than chloride originating from feed. Because only green plant material stabilised acid base balance, chlorophyll and its metabolites are discussed as potential mediators of the effect of green fodder on acid base balance.