Dairy cows grazing high-digestibility pastures exhibit pronounced diurnal variation in ruminal pH, with pH being below values considered optimal for digestion. Using a dual-flow continuous culture system, the hypothesis that minimizing diurnal variation in pH would improve digestion of pasture when pH was low, but not at a higher pH, was tested. Four treatments were imposed, with pH either allowed to exhibit normal diurnal variation around an average pH of 6.1 or 5.6, or maintained at constant pH. Digesta samples were collected during the last 3 d of each of four, 9-d experimental periods. A constant pH at 5.6 compared with a constant pH of 6.1 reduced the digestibility of organic matter (OM), neutral detergent (NDF), and acid detergent fiber (ADF) by 7, 14, and 21%, respectively. When pH was allowed to vary (averaging 5.6), digestion of OM, NDF, and ADF were reduced by 15,30, and 36%, respectively, compared with pH varying at 6.1. There was little difference in digestion parameters when pH was either constant or varied with an average pH of 6.1. However, when average pH was 5.6, maintaining a constant pH significantly increased digestion of OM, NDF, and ADF by 5, 25, and 24% compared with a pH that exhibited normal diurnal variation. These in vitro results show that gains in digestibility and potential milk production can be made by minimizing diurnal variation in ruminal pH, but only when ruminal pH is low (5.6). However, larger gains in productivity can be achieved by increasing average daily ruminal pH from 5.6 to 6.1.

A simple, specific method is described for the determination of mimosine and 3,4-dihydroxypyridine (DHP) in extracts of leaves and seeds of Leucaena glauca Benth. and in urine. Plant material is extracted with cold 0.1 N hydrochloric acid, and interfering substances are removed by chromatography on a cation-exchange resin. Organic cations are displaced from the resin with 2N ammonium hydroxide and the concentrated eluate chromatographed in one direction with the use of mesityl oxide : formic acid : water (41 : 7 : 6 by volume). The spots of mimosine and DHP, revealed with a ferric chloride spray, are cut out and the colour fully developed and measured. Urines are analysed in the same way except for a preliminary hydrolysis of the conjugated DHP. The method is satisfactory for estimating amounts of mimosine and DHP in the range 10–160 µg applied to the paper. Recoveries of these substances added to various extracts and to urine have varied between 98–102%. Appreciable destruction of mimosine, with the formation of some DHP, occurred when fresh L. glauca leaves were dried even under mild conditions. In fresh material no loss of mimosine occurred when it was placed immediately in 0.1 N hydrochloric acid. The ready hydrolysis of mimosine to DHP by boiling 0. I N hydrochloric acid has been demonstrated for the first time.

Five tropical and five temperate pasture legumes were grown in pots containing an acutely copper-deficient soil, and in water culture. Growth responses and copper contents of the tops, roots, and seed are reported. In soil culture, the relative dry matter yields of the tops of Desmodium uncinatum (Sacq.) DC., Phaseolus lathyroides L., Centrosema pubescens Benth., Indigofera spicata Forsk., and Stylosanthes bojeri Vog. on the nil treatments were 60, 46, 45, 21, and 7% respectively of their maximum yields obtained with optimum copper additions to the soil. Yields of Trifolfum repens L., Trifolium fragiferum L., Trifolium alexandrinum L., Medicago sativa L., and Medicago tribuloides Benth. on the nil treatments were 38, 31, 3, 17, and 14% respectively of their maxima. Thus Trifolium alexandrinum and Stylosanthes were the most sensitive to copper deficiency, Desmodiurm and Trifolium repens the least sensitive, the remaining species showing intermediate responses. The sensitive species required additions of copper of up to the equivalent of 4 lb copper sulphate per acre to produce maximum growth, while the relatively insensitive species required only the equivalent of ½ lb per acre. Similar results were obtained in the water culture experiment. The copper concentrations in the dry plant material from the various species did not vary significantly at any one level of application. The range of copper concentration over all treatments was 1.7–11.3 p.p.m., but the species did not differ greatly in their copper requirements for normal growth. The relatively sensitive species such as Trifolium alexandrinum and Stylosanthes were much less efficient at extracting copper in both soil and water culture than Desmodium, Trifolium repens, and Trifolium fragiferum. However, on the basis of copper uptake per unit weight of root tissue Stylosanthes had a high value, which was largely controlled by top/root ratios. Copper accumulated more in the roots than in the tops of most species, particularly at high rates of copper application; however, Stylosanthes and Trifolium alexandrinum also had relatively high copper contents in their roots on the low treatments. The seeds of these two species had higher copper contents per unit weight than the other species. It is considered that, for legumes, a copper concentration above 5 p.p.m. in the plant material is satisfactory, while 4–5 p.p.m. is marginal and less than 4 p.p.m. indicates copper deficiency. The occurrence of high copper contents in some plants showing foliar symptoms and yield depression as a result of copper deficiency is discussed.