ALBERT

Notes: A study was conducted to determine the influence of a change in herbage mass on rates of herbage growth (G), senescence (S) and net production of green herbage (NP) in swards of Lolium perenne L., Poa annua L. and Trifolium repens L. under continuous stocking with sheep. Swards were maintained at either high (1700–1900 kg OM ha−1; H) or low (700–900 kg OM ha−1; L) herbage mass from April to 20 August. From 20 August to 13 September half of the L sward was permitted to grow until a herbage mass similar to that of the H sward was achieved (LH), and at the same time half of the H sward was grazed down until a herbage mass similar to that of the L sward was achieved (HL). The other half of each sward was held at constant mass (LL and HH). Estimates of G, S and NP were obtained for each plant species over a 2-week period from 17 September to 1 October and estimates of species population densities were also made.The combined species rates of G and S per unit area were highest in treatment LH and lowest in treatment HL, whilst the rates for the LL and HH swards were intermediate. The rate of NP was similar in the LL, HH and LH treatments (34.5, 29.3, 33.6 ± 6.2 kg DM ha−1d−1) but was lower in the HL sward (100 ± 6.2). The effects of alteration of herbage mass on individual tiller or stolon G and S rates were rapid but population density changes were slower.Within the limited conditions of this trial it was not possible to increase NP by manipulation of herbage mass under continuous stocking management but the results indicate that NP can be reduced in the short term if a sward of high herbage mass and low population density is grazed hard.

Notes: A series of twenty-four swards containing different proportions of white clover (0·20-0·25) and perennial ryegrass were created by using different seed mixtures, herbicide applications and previous cutting Frequencies. These swards were used to study the diet of oesophageally-fistulated wether sheep which grazed the various swards for a 30-min period after 1, 2 and 3 weeks of regrowth.The proportion of white clover in the diet was generally greater than that in the sward. Fifty-seven percent of the variation in the proportion of white clover in the diet could be attributed to the proportion of white clover in the sward. White clover and perennial ryegrass leaf and stem were grazed to the same height and the proportion of white clover in the grazed horizon of the sward explained 83% of the variation in the proportion of white clover in the diet. The proportion of white clover in the diet was greater than the proportion in the grazed horizon of the sward in week 3 of regrowth, but not in weeks 1 and 2, and greater when the proportion of white clover in the grazed horizon was lower than 0·20. Both these observations were interpreted as indicating selection for white clover by the sheep within the grazed horizon.There was a positive and linear relationship between the depth of the grazed horizon and sward height which, together with the relationship between the proportion of white clover in the grazed horizon and in the diet, would allow the prediction of the proportion of white clover of the diet from the height and the white clover content of the grazed horizon of the sward.

Notes: A description is given of equipment designed to be fitted to either sheep or cattle, and to record automatically information on the jaw movements associated with both grazing and ruminating, movements of the head in plucking mouthfuls of herbage, and the time spent in grazing. The equipment has been successfully tested against alternative visual and mechanical methods of measuring grazing behaviour.The use of modified equipment in detailed studies has shown (a) that the maximum acceleration of the head in a longitudinal plane when plucking mouthfuls of herbage was twice as great in sheep as in cattle and in the sheep, but not in the cow, increased as sward height decreased; and (b) that the ratio of jaw movements to head movements was always greater than unity in both sheep and cattle, and was greater on tall than on short swards in two out of three comparisons. The rate of biting was significantly lower on tall than on short swards.

Notes: Six calves, six heifers and six dry cows grazed a mature sward (treatments A and B) and a leafy aftermath (treatment C) in succession. The yields of herbage on the two swards were 7100 lb and 1950 lb DM per acre (7950 kg and 2180 kg per ha), respectively. The amounts of herbage offered daily were 47 lb (21–5 kg) DM per head (treatment A), 70 lb (32 kg) (treatment B), and 60 lb (27 kg) (treatment C), Two estimates of herbage organic–matter intake (O,M,I,) were made on each treatment; records of grazing behaviour were made on treatments B and C, The digestibility of the diet selected on treatment C was higher than that selected on treatments A and B, and the animals ate significantly more O,M, on treatment C, The total grazing times on treatments B and C were similar, but the animals found it more difficult to graze on treatment BHerbage O.M.I. increased significantly from treatment A to treatment B, even though the quantity of herbage offered per day on treatment A greatly exceeded the amount eaten. The increase in O,M,I, was found to be associated with an increase in faecal 0,M, output, but the digestibility of the diet did not change.

Notes: Groups of six-month old lambs, which were either experienced or inexperienced grazers, strip-grazed swards of S24 perennial ryegrass or Hungaropoly tetraploid red clover, at daily herbage allowances of 20 or 40 g OM/kg LW, in late August and September. The swards were similar in N content, but the weight of standing crop, and its digestibility, were higher on grass than on clover. Estimates of herbage intake were made in two successive periods of 19 days. Intake (g OM/kg LW) was lower at low than at high allowance (by 22% and 28% in periods I and II). and experienced grazers ate more than inexperienced animals (by 27% and 22%). Intakes on clover were 28% higher than on grass in Period I, but in Period II the difference was not significant.

Notes: Experiments were conducted in 1967 and 1968 in which HerefordXFriesian (Experiment 1) and Friesian (Experiment 2) steer calves horn in April were turned out to graze at one week or 3 months of age, respectively, and maintained at three stocking densities in the ratio 1:2:3 animals per unit area. The calves grazed paddocks of S23 perennial ryegrass in rotation, and were moved when the height of grazed stubble at the medium stocking density was reduced to 8 cm. The rate of liveweight gain and herbage intake per head declined as stocking rate increased. When the results of the two experiments were compared, the weight gain of the calves was more closely related to the weight of herbage residues than to the height of the grazed sward. The rate of liveweight gain was depressed when the amount of herhage left after grazing fell helow 2000–2500 kg OM/ha (1800–2250 Ib/ac).

Notes: Five pasture treatments: (1) controlled grazing, (2) controlled grazing + lime, (3) controlled grazing + lime + phosphate, (4) controlled grazing + lime + phosphate + oversown white clover and (5) controlled grazing + lime + phosphate + oversown white clover + oversown perennial ryegrass were applied to three semi-natural hill grassland communities. The communities were those dominated by Agrostis/Festuca, Molinia and Nardus. The proportion of Nardus at the Nardus-dominant site was substantially reduced by herbicide before treatments were applied. All treatments were grazed simultaneously by mature wether sheep on three occasions each year. There were two grazing periods each of 4 weeks duration between mid-May and mid-August with a further grazing period of 3 weeks starting mid-October. During each grazing period stock numbers were set so that a residual herbage mass of 560 kg DM ha −1 remained at the end of the grazing period. Measurements of net herbage accumulation (NHA) were made annually over a period of 13 years at each site. The green:dead ratio of grasses, species composition of the pasture and the pH of the soil were measured at intervals during the experiment.Estimates of mean annual NHA ranged from 3860 kg DM ha−1 for treatment 1 (controlled grazing) to 5170 kg DM ha−1 for treatment 5 (oversown white clover and perennial ryegrass). The application of lime and phosphate increased annual NHA by 300–350 kg DM ha−1 with a further increase of around 400 kg DM ha−1 when white clover was sown. Increases in NHA between year 1 and year 13 ranged from 30% for treatment 1 to around 55% for treatment 5. Although there was no difference in the mean NHA between sites, the herbage from the Agrostis/Festuca site contained a higher proportion of green grass and white clover than that from the other sites. The highest levels of green grass and white clover were found on the oversown treatments at each site.The grazing pressure exerted produced relatively little change in the botanical composition at the Agrostis/Festuca site. At the Molinia-dominant site the Molinia was largely replaced by Nardus during the first 6 years and Nardus also increased in cover at the Nardus site. Application of lime and phosphate generally increased the proportion of Poa pratensis, Festuca rubra and Agrotis tenuis but did not halt the spread of Nardus at the Molinia and Nardus sites. White clover and perennial ryegrass were successfully introduced by oversowing and proportions remained high throughout the 13 years. The cover by bryophyte spp. increased at all sites with the greatest increases occurring in each case on the less comprehensive pasture treatments.These results suggest that on Agrostis/Festuca-dominant pastures herbage biomass production can be increased with relatively low-cost pasture treatments while maintaining Species diversity. However, Nardus and Molinia dominant pastures are likely to require more comprehensive pasture treatments involving sown grasses and white clover to provide herbage of acceptable quality and avoid an increase in Nardus and bryophytes in the sward. With a regime of episodic summer grazing and the addition of fertilizers oversown pastures can be maintained over long periods of time.

Notes: The results are reported of an examination of detailed measurements on the ingestive behaviour of calves and lambs in response to variations in the surface characteristics of swards under strip-grazing and continuous stocking managements. It is shown that intake per bite and the short-term rate of herbage intake were both sensitive to the height of the surface horizon above ground level but, at least under strip-grazing management, not to variations in herbage density in the grazed horizon. The rate of biting was less sensitive to variations in sward conditions, particularly under strip-grazing.Both intake per bite and rate of intake were more sensitive to variations in grazing height under strip-grazing, where sward changes were rapid, than under continuous stocking, where they were slow. Under continuous stocking, ingestive behaviour was more sensitive to changes in sward conditions in lambs than in calves.

Notes: Two experiments are described in which groups of lactating cows, non-lactating cattle and weaned calves grazed a sequence of swards varying in maturity and herbage mass under strip grazing management at a daily herbage allowance of 60 g dry matter per kg live weight. Lactating cows ate 43% and 76% more herbage than non-lactating cattle of similar weight in the two experiments but herbage OM intakes per unit live weight by the calves and lactating cows were similar.Variations in diet digestibility and herbage intake in the lactating and non-lactating cattle with changes in sward conditions were similar. In the first experiment the calves were experienced grazers; the variation in the digestibility of the herbage selected was less in the calves than the adult cattle, but the variation in herbage intake was greater. The calves in the second experiment were younger, and they were inexperienced grazers; their ability to increase herbage intake in response to changing sward conditions was poorer than that of adult cattle, though variations in diet digestibility were similar in all classes.The practical implications of these results are discussed briefly.

Notes: Two experiments are described in which two levels of winter feeding and three levels of herbage allowance during the grazing season were imposed upon March/April calving British Friesian dairy cows. The winter treatments resulted in differences in live weight and milk yield at turnout of 35 and 53 kg and 3·4 and 3·2 kg d-1 for the two trials. Subsequently, when grazed at generous herbage allowances, the cows were able to compensate for much of this difference but when herbage was restricted the milk yield differences were accentuated.Groups of cows from each winter treatment were offered 25, 50 or 75 (Experiment 1) and 30, 50 or 70 (Experiment 2) g herbage DM per kg LW daily during the grazing season. Daily herbage intakes on the three allowances in each trial were 14·1, 13·3, 10·7 and 12·5, 12·1, 11·5 kg OM and milk yields were 16·0, 15·3, 12·5 and 15·2, 14·3, 11·8 kg SCM respectively. Both intake and milk production were depressed once the cows were forced to consume more than 50% of herbage on offer or to graze the sward down to a mean height of less than 8–10 cm. Grazing behaviour observations indicated that under rotational managements the cows did not compensate for restrictions in available herbage by grazing longer. Highest levels of milk production per unit area were observed in both trials when production per cow was depressed by 20–25%.