ALBERT

Notes: Measurements of rates of growth and senescence of leaf lamina per tiller and of changes in tiller population densities were made in three experiments designed to investigate the influence of sward slate on leaf turnover and net production under continuous stocking.In each experiment initially uniform swards were fenced to provide four plots on which animal numbers were adjusted twice weekly to give a series of swards maintained as nearly as possible in a steady state with respect to sward surface height (range 1.1–6.4 cm) and herbage mass (range 440–2690 kg OM ha−1). Two experiments were carried out in July–September on vegetative swards and one in May–June on a reproductive sward. Measurements were begun 3–7 weeks after treatments were started and were repeated weekly during 3–4 week measurement periods.In all three experiments the rate of lamina growth per tiller increased linearly with an increase in sward surface height and herbage mass. In the two experiments conducted in July–August this relationship was partially offset by a linear increase in the rate of senescence per tiller but net production per tiller also increased linearly in relation to sward height and mass. In the experiment conducted in May–June the rates of growth and senescence per tiller increased in parallel so that net production per tiller showed no relationship with sward condition.Tiller population densities in the July–August experiments were highest in swards maintained between 2 and 3 cm surface height and declined in swards maintained above and below this height. In the experiment in May–June tiller numbers were similar in all treatments prior to the summer solstice but diverged in a manner similar to the other experiments later in the year.The rate of lamina growth per unit area increased in a manner consistent with an asymptotic relationship and the rate of senescence increased linearly with increasing sward height and mass in all three experiments. Net production per unit area was reduced on swards below about 2.5 cm in height but was insensitive to variation in sward surface height between 2.5 and 6.0 cm (approximately 1000–2500 kg OM ha−1 herbage mass).The effectiveness of adjustments in tiller numbers and production per tiller and of changes in the balance between growth and senescence as mechanisms of sward homeostatis, together with their implications in the scope for manipulating herbage production by grazing management are discussed briefly.

Notes: There was a three-fold variation in epicuticular wax content between populations of white clover and a five-fold variation between populations of red clover. The mean for all populations of red clovers was twice that of white. There was also a two- to three-fold variation within each population.The epicuticular wax content of white and red clovers grown in the field showed an increase with age. Thin layer chromatography showed no qualitative differences in the epicuticular waxes extracted either between populations or with sampling date.The higher levels of epicuticular wax found in some clovers were considered to be of possible significance as a source of antifoaming compounds in bloat-inducing pastures.

Notes: Differences in ease of digestion of bundle sheath cell walls of leaf blades of Panicum spp. are shown to be associated with differences in bundle sheath cell wall structure, including the presence or absence of a suberized lamella. These structural differences are correlated with photo-synthetic type (viz. C3, intermediate C3/C4, and the C4 types, PCK, NADP-ME and NAD-ME), as are mesophyll: bundle sheath area ratios.

Notes: The construction of a transducer and the use of a recording system to measure jaw movements of grazing sheep is described, The time spent grazing, ruminating and idling may be measured by this equipment and the data produced automatically processed using a microprocessor which determines each minute whether the animal is grazing, ruminating or idling and also summarizes these data to give total times. The accuracy of this technique in relation to manual observation is discussed.

Notes: The effect of two heights of cutting (5 and 8 cm) on the dry matter harvested and persistency of a range of different grass species and varieties were monitored over a 3-year period (1976 to 1978). Dry matter harvested was measured in the second and third harvest year and persistence of sown grass was assessed at the end of the first and third harvest year. The grasses were managed under a frequent cutting system, i.e. simulated grazing. Results showed that at the low cutting height tetraploid hybrid ryegrasses and diploid Italian ryegrasses in the third harvest year gave lower annual dry matter harvests of sown grass and were less persistent than at the high cutting height, whilst, in contrast, perennial ryegrasses gave higher annual harvests of sown grass but persistency was unaffected. In general at the low cutting height varieties of cocksfoot, meadow fescue and tall fescue gave comparatively higher annual harvests of sown grass in the second harvest year but lower yields of sown grass in the third harvest year. A notable exception was Cambria cocksfoot which in the second harvest year gave higher yields of sown grass and was more persistent at the low cutting height.However, at 5 cm cutting height, the proportions of weed grasses (mainly Poa spp.) in swards sown to tetraploid hybrid ryegrasses and diploid Italian ryegrasses were generally greater, particularly in mid-season.

Notes: Laminae of Lolium perenne and Phleum pratense were tested mechanically and the results analysed using engineering composite theory and fracture mechanics. As the lamina dries the fibres double in stiffness. The intervening cells show a sevenfold increase in stiffness below 20% water content (based on dry weight). Work to fracture across the veins is almost independent of water content, but below 50% water content the mode of fracture changes. It is predicted that total fibre content will not affect hay shatter; total protein content may affect it by altering the water-binding properties.

Notes: Grass silages made from first-harvest perennial ryegrass in mid-May and early-June and termed high-D and low-D respectively had mean DOMD values of 694 and 633 g kg−1 and were offered ad libitum to twelve Ayrshire cows in a 16-week feeding experiment using a cyclic changeover design. The silages were supplemented with a concentrate containing 363g CP per kg DM at daily rates of 1.5, 3.0 and 4.5 kg per cow. The average daily intakes of silage DM were 12.6 and 11.1 kg per cow on the high- and low-D silage treatments respectively, and were not significantly different on the three concentrate treatments. The mean daily milk yields were 171, 18.6 and 21.0 kg per cow on the low-D silage treatments, and 19.6, 21.2 and 22.8 kg per cow on the high-D silage treatments at the 1.5, 3.0 and 4.5 kg rates of concentrate feeding respectively. Fat and lactose concentrations in the milk were not affected significantly by treatment, whereas the CP and SNF concentrations increased progressively and significantly as the rate of supplementary feeding increased. It is concluded that a high-protein concentrate supplement allows silage to make the maximum contribution in the diet, and gives a high response in terms of milk yield and composition.

Notes: Grass which had grown without interruption from late April was cut as for hay in early July in each of 2 years. Fifteen dates of removal of the cut herbage were compared ranging, at 1-d intervals, from the day of cutting to 14 d after cutting. Sward regrowth was studied.A delay of 5 d in removing cut herbage reduced herbage dry matter harvested during the remainder of the growing season by 9% and a delay of 10 d reduced yield by 16%. Delaying the removal of cut herbage reduced the density of grass tillers considerably in the short term, but the effect had worn off in 8 to 12 weeks. The presence of cut herbage reduced the rate of extension of leaf blades considerably. Delaying the removal of cut herbage reduced the area per leaf blade and the weight per unit area and these effects persisted for several weeks. Grass growing under cut herbage had a less negative leaf water potential and a rather cooler but much darker environment in which to grow than uncovered grass.

Notes: Book reviews in this article: Milk from Grass Edited by C. Thomas and J. W. O. Young Nitrogen Fixation in Legumes Edited by J. M. Vincent Herbage Intake Handbook Edited by J. D. Leaver Man's Proper Study By Richard J. Colyer Introduction to Sheep Fanning By R. G. Johnston

Notes: Information about the grazing behaviour and the return of dung to pasture by lactating dairy cows was collected from stocking rate experiments in northern Victoria. Grazing behaviour was observed for 24-h periods in mid-summer in two years. Grazing time increased as herbage allowance decreased to about 32 kg DM cow−1 d−1 but as herbage allowance decreased further grazing time also decreased. A herbage allowance of 32 kg DM cow−1 d−1 corresponded to a stocking rate of about 5.5 cows ha−1. This effect of herbage allowance on grazing time may have been confounded by herbage mass, however. Rumination time of the cows increased by 003 h for each kg increase in herbage allowance while resting time was not affected by treatment.The effects of stocking rate on some of the characteristics of faecal output were measured for a 3-d period in mid-summer. The number of pats deposited per cow daily declined by 0.66 for each unit increase in stocking rate. The fresh weight of dung also declined as stocking rate increased by 0.16 kg per unit of stocking rate. While the values for the amounts of dung deposited on the pasture by the cows at the lower stocking rates are similar to many of those reported in the literature, this study has quantified the way in which stocking rate may influence this in one instance. Furthermore, provided that some measure of herbage intake is made when measurements of dung excretion are performed, it is suggested that estimates of in vivo digestibility can be obtained.