Metabolic adaptations of mullet Rhinomugil corsula (Hamilton) with special reference to energy utilization

While the respiratory quotient (R.Q.) of Rhinomugil corsula in air-saturated water remains near unity at all levels of random activity, the ammonia quotient (A.Q. = volume or mole: mole relation of ammonia excreted to oxygen consumed) is higher at lower levels of activity, indicating relatively higher protein utilization in less active fish. The mean routine R.Q. values of R. corsula in air-saturated water at temperatures of 30 and 35°C are 0.91 and 0.95 respectively. Assuming that the major sources of ammonia excreted are certain predominant free amino acids, an estimate of caloric break-up of routine meta-bolism of R. corsula suggests that the fish is completely aerobic in air-saturated water and that it derives 14, 44 and 42% of energy from proteins, carbohydrates and fats respectively from a total of 567 cal/kg fish/h at 30°C (15, 55 and 30% at 35°C). At oxygen concentrations below air saturation, R.Q. and A.Q. values of R. corsula increase with decrease in ambient oxygen indicating an increase in anaerobic metabolism and protein utilization. The correlation between the trends of R.Q. and A.Q. levels are similar to that observed earlier in Tilapia mossambica. During hypoxia (1.6 mg O₂/l at 30°C) R. corsula derives about half its energy for sustenance and activity anaerobically. The mullet does not appear to accumulate an oxygen debt during hypoxia.     

A NOTE ON THE ZERO-GRAZING OF BEEF CATTLE

Groups of 8 steers weighing 300–400 kg (660–880 Ib) were rotationally grazed on a ryegrass-dominant pasture for 115 days. The systems compared were zero grazing (Z), field grazing conducted at the same stocking rate (FC), and field grazing conducted at a stocking rate varied with the intention of giving the same liveweight gain per uiimal as zero grazing (FV). Mean daily liveweight gains were: Z, 0.98; FC, 0.78; FV, 0.90 kg/animal (2.2, 1.7 and 20 Ib/animal), and liveweight gains/unit area were in the ratio 100:78:85. Organic-matter intake, measured on four occasions, was, on average, Z, 6.54; FC, 6.18; FV, 687 kg/head daily (14.4, 13.6 and 15.1Ib). From these results it appears that a comparison of zero grazing and field grazing made at the same stocking rate is likely to underestimate the potential of field grazing for beef production from grass.     

A NOTE ON THE SUITABILITY OF THE IN VITRO DIGESTIBILITY TECHNIQUE FOR VERY SMALL PLANT SAMPLES

The two-stage in vitro digestibility technique was scaled down to use 0.1 g samples. The accuracy of predicting in vivo DM digestibility by the use of micro-samples was studied, using 35 samples of four grass species of known in vivo digestibility. When the sample size was reduced from the normal 0.5 g to 0.1 g, the residual standard deviation of the regression relating in vitro to in vivo DM digestibility was increased from ±2.5 to ±3.4 digestibility units. Grinding the samples more finely than through a 1.0 mm screen did not improve the accuracy of predicting in vivo digestibility. It was concluded that the in vitro method may be used with micro-samples where necessary, but with less accuracy than the macro-technique. For maximum accuracy, the use of standards of known in vivo digestibility is necessary.     

The Effect of Gravity on Root Emergence from Cuttings of Some Tree Species

Poplar shoots trained horizontally and normally growing shootswere used to compare the effect of horizontal and vertical orientationin summer on the subsequent rooting of terminal cuttings; asignificantly greater number of preformed roots emerged fromcuttings of vertical shoots. This difference in rooting abilitymay be due to the lower concentration of indolyl-acetic acidin the upper than in the lower half of horizontal poplar stemsas shown by Leach and Wareing (1967). Decapitation of a seriesof these poplar cuttings (Populus ? robusta Schn.) showed thatwound-root production was influenced by the larger terminalbuds on vertical than on horizontal shoots. From a comparison of horizontal and vertical storage of applerootstock cuttings at 45 ?F in the autumn, 29 per cent moreof the horizontal cuttings than the vertical ones had a basalcallus in the following February. Of these cuttings which madesatisfactory shoot growth (over 5 cm) in the following summer,horizontal cuttings exceeded vertical ones by 80 per cent; aresult which was correlated with root production. In a second experiment with M II apple rootstocks in which cuttingswere both stored and grown at the same angle more roots occurredon cuttings placed horizontally rather than vertically, andthis orientation also induced the rootings of a greater proportionof leafy Worcester Pearmain apple cuttings.     

THE ERROR IN PREDICTING PASTURE DRY–MATTER DIGESTIBILITY FROM FOUR DIFFERENT METHODS OF ANALYSIS FOR LIGNIN

The lignin content of 50 samples of five grasses of known in vivo digestibility were determined by the methods of Armitage, van Soest and two modifications of the van Soest technique. The error in predicting DM digestibility varied from ±3.1 for tbe Armitage metbod to ±5.0 for the van Soest method. This error compares nnfavourably witb ±2.1 previonsly obtained on tbe same samples with the in vitro technique of Tilley and Terry.     

Sectional notes

American Journal of Potato Research -