ALBERT

Notes: An early-heading variety of perennial ryegrass (Ramore) bred for high magnesium (Mg) content was compared with an early control variety (Frances) for its ability to increase Mg intake, Mg utilization and blood Mg concentration in sheep, and so reduce the incidence of hypomagnesaemic tetany. Swards of the two varieties were established and each was grazed by ewes suckling twin lambs from turn-out to weaning and thereafter by dry ewes. In early and late season herbage from a proportion of each sward was cut daily and fed fresh to ewes housed indoors in metabolism crates.Under grazing conditions herbage from Ramore swards had, over the 1992 and 1993 grazing seasons, a higher Mg concentration than Frances (2.35 g kg−1 vs. 2.18 g kg−1; s.e.m. 0.019, P〈 0.001). During the spring period there was a higher (P 0.001, s.e.m. 0.0074) Mg concentration in the blood of ewes grazing Ramore (0.854 m mol 1−l) swards compared with those grazing Frances (0.793 m mol 1 −1) whereas during the autumn period blood Mg concentrations were higher in ewes grazing Frances. Ewe and lamb liveweight gains, recorded in 1992 only, were higher on Ramore swards than on Frances swards, although the difference was not significant.Indoor feeding studies showed that Mg intake was significantly higher (P〈 0.001, s.e.m. 0.026) in ewes offered Ramore (1.98 g d−1) herbage compared with those offered Frances (1.74 g d−1) herbage with no significant difference in dry-matter intake between the two varieties. Apparent availability and retention of Mg were higher for animals fed Ramore during the spring feeding periods than those fed Frances, but during the autumn feeding periods the reverse was true. Under indoor feeding conditions, variety had no significant effect on blood Mg concentrations.It was concluded that under grazing conditions a high Mg variety could provide an effective means of reducing the incidence of hypomagnesaemic tetany.

Notes: The effects of continuous stocking by sheep at sward surface heights (SSH) of 3, 5, 7 and 9 cm in grass/clover (GC) and nitrogen-fertilized grass (GN) swards were examined in relation to herbage mass and quality, clover content, tiller density and rates of herbage production and senescence in two periods in each of three grazing seasons (1987-89). The GN swards received a total of 300 kg N ha−1 each year in six equal dressings from March; GC swards received a single dressing of 50 kg N ha−1 in March each year.Herbage mass measured from ground level increased linearly with SSH with overall mean herbage masses of 0·89, 1·38, 1·78 and 2·12 t OM ha−1 (s.e.m.0·024, P 〈 0·001) at SSH of 3, 5, 7 and 9 cm respectively. GN and GC swards had mean herbage masses of 1·58 and 1·51 t OM ha−1 (s.e.m. 0·051, NS) respectively. Mean N content of herbage on GN swards was greater than that on GC swards and declined with increasing SSH. Crude, fibre (CF) content of herbage was similar for both sward types and increased with increasing SSH.Clover content of GC swards remained low throughout the experiment, ranging from 0·002 to 0·074 of herbage mass. However, from tissue turnover rates it was estimated that its contribution to herbage production was in the range of 0·049–0·219 of net herbage growth.Total growth increased with increasing SSH in both sward types, with maximum growth rates in GN swards of 143 and 130 kg DM ha−1 d−1 and in GC swards of 88·2 and 85·4 kg DM ha−1 d−1 in Periods 1 (up to early July) and 2 (after July) respectively. Senescence rates ranged between 13·3 and 50·1 kg DM ha−1 d−1 and tended to be higher in Period 2 than in Period 1. Net production increased with increasing SSH in Period 1, while in Period 2 net production declined at SSH above 6·5 cm.The increased net herbage production in taller swards was not associated with greater utilized metabolizable energy production at sward heights above 5 cm.

Notes: Vernalized and unvernalized perennial ryegrass (Lolium perenne cv. Gremie) tillers planted in microplots in a glasshouse in April 1974 and 1975 were exposed to natural daylength thus inducing vernalized plants to produce reproductive, and unvernalized plants vegetative growth. Nitrogen was applied at 0–30 g m−2 (to 24 g m−2 in 1975) to both types of herbage. At the first defoliation in each year yields from vernalized grass were greater than those from unvernalized grass; subsequently differences were minimal or reversed. Vernalization had no significant effect (P 〉 0.05) on total yields over four defoliations in either year.Apart from the first cut in 1974 nitrogen application increased dry matter yields of both types of herbage. Tiller numbers were usually increased by the lowest level of nitrogen application but at higher levels the effect was variable.There was no evidence of an interaction effect of level of nitrogen application and vernalization on dry matter yields.

Notes: Over three grazing seasons (1984-1986) a sward of perennial ryegrass, cv. Talbot, which received a total of 336 kg N ha-1 each season, was cut or grazed with ewes at 3- or 4-week intervals on a rotational basis.Sward productivity was higher under cutting than under grazing irrespective of the interval between defoliations. Under cutting, mean herbage organic matter (OM) yields over both intervals were 8·66, 9·62 and 8·17 t ha-1 in 1984, 1985 and 1986 respectively while under grazing the corresponding yields were 7·65, 8·63 and 7·50 t ha-1. The mean annual yield of herbage defoliated at 3-week intervals was 7·50, 8·64 and 7 ·20 t OM ha-1 compared with 8·80, 9·60 and 8·46 t OM ha-1 for swards defoliated at 4-week intervals in the three years respectively.The nitrogen (N) content of both the available and the residual herbage was consistently higher under grazing than under cutting. Available herbage contained 31·3 and 27·7 g N kg OM-1 and residual herbage 26·1 and 22·7 g N kg OM-1 under grazing and cutting respectively.The mean yield of N under cutting was 284 kg ha-1 compared with 304 kg ha-1 under grazing. Defoliation interval had no effect on N yield, the overall mean yield being 294 kg ha-1 under both 3- and 4-week defoliation intervals. The effect of the treatments on tiller population was slight and inconclusive.The process of grazing reduced yield probably as a result of damage to the sward through trampling; the positive effect of excretal N on yield was minimal on account of the short grazing periods.

Notes: Plots of an established perennial ryegrass sward (cv. Talbot) fertilized with 100 or 300 kg N ha−1 were harvested with one of three plot mowers; an Agria with 38-mm finger spacing and an Allen Mayfield with 38-mm finger spacing or 78-mm finger spacing. The choice of mower was arranged factorially with four post-harvest treatments: no post treatment; a second (cleaning) cut using the same mower and cutting in the same direction as the first (sampling) cut; a cleaning cut using the same mower, but in the opposite direction to the sampling cut; and a cleaning cut using a rotary mower. Sward productivity as organic matter (OM) was measured over four harvests at 6- to 7-week intervals. The Agria mower resulted in 12·3 and 15-9% more OM yield than the Allen Mayfield fitted either with knife-bars at a similar spacing, or with wider-spaced fingers, respectively. Yield of OM in the subsequent cut was reduced when a cleaning cut was taken; particularly when it was taken in the opposite direction to the sampling cut or when using a rotary mower.

Notes: In two experiments (1990 and 1991) perennial ryegrass (cv. Talbot) pasture was subjected to six different management treatments by adjusting stock numbers to achieve set sward heights for set periods between turn-out in early April and weaning in early July. The main objective of the experiments was to measure the effect of differences in sward management up to July on subsequent sward type, and the effect of sward type on the performance of weaned lambs between mid-July and early October when all swards were grazed at a sward height of 7 cm. In Experiment 1 swards were grazed at 7 cm initially and then reduced to 3 cm at various dates and maintained at 3 cm until early July. In Experiment 2 swards were grazed initially at 7 cm, and this was reduced to 3 cm and then allowed to return to 7 cm at various dates up to early July.Grazing at a sward height of 7 cm up to weaning, in early July, gave mean twin lamb growth rates of 310 g d−1, while at a tower sward surface height of 3 cm lamb growth rate was reduced to 206 g d−1 The density of seed heads produced from July was strongly influenced by earlier management. Grazing at 7 cm up to July gave a high density of seed heads (213m−2), and this reduced (126 m−2) by grazing to 3 cm. Seed heads were almost eliminated (17 m−2) by grazing at 7 cm until late June followed by grazing down to 3 cm in early July. Reducing sward surface height from 7 cm to 3 cm at an earlier date tended to increase the development of seed heads from early July. Where swards were grazed from 7 cm to 3 cm and then allowed to return to 7 cm, the later in the pre-weaning period this took place the greater the reduction in seed head development. Greater seed head density was associated with a significant decrease in the nitrogen content of the herbage on offer in Experiment 2, but an increase in modified acid detergent (MAD) fibre content was not significant.Despite the differences in the sward type on offer, the effect on weaned lamb growth rate was small. Lamb liveweight gain during autumn was significantly reduced in Experiment 2 following earlier grazing at 7 cm compared with 3 cm, but liveweight gain differences in Experiment 1 were not significant.

Notes: Over a 3-year period the productivity of perennial ryegrass (Lolium perenne L., cv. S24) swards as influenced by variations in the time of initial defoliation and close (2·5 cm) and lax (8 cm) defoliation was studied. Treatments with initial defoliations in the early vegetative stage, stem elongation and flowering stages of growth gave higher annual yields than treatments in which the initial defoliation was taken at an intermediate stage of growth when the majority of the stem apices had just been elevated above the height of defoliation. Initial defoliation treatments which removed a high proportion of apical meristems while the yield at the initial defoliation was still low produced the lowest annual yield. Consistent lax defoliation reduced yield by 14·5% compared with continual close defoliation. However, taking an initial lax defoliation followed by subsequent close defoliations produced a slight yield advantage of 4·8% over consistent close defoliation. The results are discussed in relation to other research findings and the practical implications commented upon.

Notes: Results of experiments where timothy, perennial ryegrass and mixtures of these two in the presence and absence of white clover and receiving various nitrogen treatments were compared, have been considered in the light of previous related experiments. There is evidence that under certain conditions greater yields of sown grass can be achieved from mixed seedings than from either of the two grasses on its own. No yield advantage was gained from mixtures of species when cut infrequently after a late first cut. Inclusion of white clover changed the balance of species in favour of perennial ryegrass and no yield advantage occurred with mixtures in the presence of clover. Yield advantage may be related to seasonal changes in the order of dominance of the two grass species in mixed seedings.

Notes: The influence of length of first growth period of the season and level of nitrogen application on yields of leaf and stem components of perennial ryegrass was estimated. Three primary growth periods of 21, 42 and 70 d were used in combination with nitrogen treatments allowing 0, 1.43, 2.86 and 429 kg N per ha per d of growth applied as a single dressing at the beginning of the growth period. Increases in level of nitrogen application and in growth time produced higher yields of both components, but particularly of stem. Mean leaf yield per tiller reached a maximum with a 42-d growth period.Whilst the ratio of leaf: stem was altered markedly by longer growth periods it was apparently unaffected by nitrogen application.

Notes: Early-weaned lambs were offered rations of conventional concentrate, dried grass and dried white clover pellets ad libitum for 52 days. In vivo OM digestibility coefficients of concentrate, grass and clover were 80.0, 53.4 and 66.6% respectively. Dry matter intake of dried grass was similar to that of concentrates but supported significantly lower (P 〈 0.001) daily gains (0.18 kg). Supplementation of dried grass with an equal proportion of dried clover significantly increased (P 〈0.05) DM and DOM intake and daily gains. Daily gains by lambs offered the 1:1 grass:clover diet (0.29 kg) were similar to gains by lambs offered either dried clover (0.30 kg) or concentrates (0.30 kg).