Overall, the abaxial stomatal density and leaf area of bluebunch wheatgrass were plastic in their response to water and temperature manipulations. Although bluebunch wheatgrass has the potential to adapt to changing climate, the grass is limited in its ability to respond to a combination of reduced water and increased temperature.

The composition and digestibility of ungrazed rape and of rape selected for similarity to that chosen by grazing wethers were determined. The composition of the rape consumed by these wethers was deduced from the content and digestibility of proximate constituents of the feeces. The digestibility of dry matter declined with delayed sowing and grazing.The digestive capacities of three wethers, for rape, were almost identical; a fourth was 2% lower. The digestibility of selected rape was only 0.4% higher than that of un grazed rape and the difference was not significant. The composition of selected rape was intermediate between that of ungrazed and grazed rape. However, the latter was markedly lower in ether extract and crude protein and higher in crude fibre. Hand selection of rape similar to that chosen by the grazing wethers was thus only partly successful. The digestibility of leaf was little more than 2% higher than that of stem plus petiole, a smaller difference than was expected. Despite real differences in chemical composition, the nutritive value of grazed rape was only slightly lower than that of ungrazed rape. This illustrates the important effect of organic matter digestibility on food value.Although selective grazing clearly occurred, the effect on food value was negligible.

No abstract

Wastage associaled with the grazing of rape by harnessed wethers was measured by forage sampling and by total faecal collection, to estimate intake from the consumption/excretion ratio. Blocks were grazed in accordance with Iamb fattening practice. Stubble residues wasted amounted to 18% of both the dry matter and organic matter offered. The wastage of starch equivalents was slightly lower. Grazing wastage averaged 17% of the dry matter and 20% of the organic matter. The wastage of starch equivalents was slightly higher. The mean digestion wastage was 10% of the dry matter and 7% of the organic matter of the rape offered. Only 56% of the rape dry matter offered was used for growth and maintenance. There was differential wastage of proximate constituents amounting to 95% of ether extract, 67% of crude protein and 38% of crude fibre. The wastage of nitrogen-free extract, by far the largest fraction, was similar to that of organic matter. The results were in agreement with the hypothesis that, over the normal range of yield, a doubling of yield is accompanied by a quadrupling of grazing wastage. There appeared to be relationships between yield and other sources of wastage and between stubble wastage and gqzing intensity. Further investigation of factors associated with crop and animal management is warranted if fuller utilisation of crop forages is to be achieved. It is evident from the results of this experiment that yields obtained from cutting cannot be safely used to predict animal production.

Leaf-rust infection of severity 3–4 on the modified Cobb scale reduced the dry-matter yield of Dun oat leafage by 30% and N.I.A.B. ryecorn by 23%. The reduction in root growth of ryecorn was similar to that of the aerial parts.The dry-matter percentage of the green forage was significantly increased in two of the three experiments. Palatability reduction due to leaf rust is suggested from field observations.With Dun oats leaf-rust infection increased the percentage of crude protein (C.P.) by a fifth, of ash by a tenth and decreased that of crude fibre (C.F.) by an eighth, and of nitrogen-free extract (N.F.E.) by a nineteenth. With ryecorn, rust increased the percentage of c.p. by a fourteenth, of ash by a fifth, and decreased that of N.F.E. by a twentieth.The decreased forage yield caused by rust is in accord with the results of experiments of other research workers and with field observation. The effect of rust on proximate constituents was interpreted as an improvement to feed value. This agrees with the results of most reported experiments but conflicts with the field evidence.The hypothesis that leaf rust affects forage composition mainly by reducing the physiological age of cereals is proposed.