An investigation into the grazing efficiency of perennial ryegrass varieties

The objective of this study was to compare the grazing efficiency of 30 perennial ryegrass varieties, differing in ploidy and heading date. Plots were grazed by lactating dairy cows and managed under a rotational grazing system with 19 grazing events occurring over two years. Pre-grazing and post-grazing compressed sward heights were measured with a rising plate meter. A mixed model was used to predict the post-grazing sward height of each variety based on year, grazing event, block and pre-grazing sward height. Residual grazed height (RGH) was derived as the difference between the actual and predicted post-grazing sward height and was used as the measure of grazing efficiency. Negative RGH values indicated that the actual herbage removed was greater than that predicted and so indicated a superior grazing efficiency. Varieties differed in their level of grazing efficiency (p < .001), with RGH values ranging from −0.38 to +0.34 cm. Tetraploid varieties exhibited significantly greater grazing efficiency performance than diploids (p < .001), with average RGH values of −0.13 and +0.13 cm respectively. A significant difference in grazing efficiency was found among recommended perennial ryegrass varieties that are not being recorded by mechanically harvested simulated grazing protocols. A variety reappraisal that included grazing efficiency could identify varieties capable of improving on-farm livestock productivity from grass.     

Effects of perennial ryegrass (Lolium perenne L.) cultivars on herbage production, nutritional quality and herbage intake of grazing dairy cows

Four perennial ryegrass (Lolium perenne L.) cultivars were compared for differences in herbage production, nutritive value and herbage intake of dry matter (DM) during the summers of 2002 and 2003. Two paddocks were sown with pure stands of four cultivars in a randomized block design with three replicates. Each plot was subdivided into fourteen subplots (22 m × 6 m) which were grazed by one cow during 24 h. Twelve lactating dairy cows were assigned to one cultivar for a period of 2 weeks in a 4 × 4 Latin square experimental design; the experiment lasted 8 weeks in each year. Sward structure (sward surface height, DM yield, green leaf mass, bulk density and tiller density) and morphological characteristics were measured. The ash, neutral‐detergent fibre, acid‐detergent lignin, crude protein and water‐soluble carbohydrate concentrations, and in vitro digestibility of the herbage were measured. The sward was also examined for infestation by crown rust (Puccinia coronata f. sp. lolii). Herbage intake of dairy cows was estimated using the n‐alkane technique. Cultivar differences for all sward structural characteristics were found except for bulk density and tiller density in 2003. Cultivars differed for proportions of pseudostem, stem (in 2003 only) and dead material. The chemical composition of the herbage was different among cultivars, with the water‐soluble carbohydrate concentration showing large variation (>0·35). Cultivars differed in susceptibility to crown rust. Herbage intake differed among cultivars in 2002 (>2 kg DM) but not in 2003. Herbage intake was positively associated with sward height, DM yield and green leaf mass. Canopy morphology did not affect herbage intake. Crown rust affected herbage intake negatively. It was concluded that options for breeders to select for higher intake were limited. High‐yielding cultivars and cultivars highly resistant to crown rust were positively related with a high herbage intake.     

Effect of grazing severity on perennial ryegrass herbage production and sward structural characteristics throughout an entire grazing season

The objective of this study, which was part of a larger grazing‐systems experiment, was to investigate the cumulative impact of three levels of grazing intensity on sward production, utilization and structural characteristics. Pastures were grazed by rotational stocking with Holstein–Friesian dairy cows from 10 February to 18 November 2009. Target post‐grazing heights were 4·5 to 5 cm (high; H), 4 to 4·5 cm (intermediate; I) and 3·5 to 4 cm (low; L). Detailed sward measurement were undertaken on 0·08 of each farmlet area. There were no significant treatment differences in herbage accumulated or in herbage harvested [mean 11·3 and 11·2 t dry matter (DM) ha^?1 respectively]. Above the 3·5 cm horizon, H, I and L swards had 0·56, 0·62 and 0·67 of DM as leaf and 0·30, 0·23 and 0·21 of DM as stem respectively. As grazing severity increased, tiller density of grass species other than perennial ryegrass (PRG) decreased (from 3,350 to 2,780 and to 1771 tillers m^?2 for H, I and L paddocks respectively) and the rejected area decreased (from 0·27 to 0·20 and to 0·10 for H, I and L paddocks respectively). These results indicate the importance of grazing management practice on sward structure and quality and endorse the concept of increased grazing severity as a strategy to maintain high‐quality grass throughout the grazing season. The findings are presented in the context of the need for intensive dairy production systems to provide greater quantities of high‐quality pasture over an extended grazing season, in response to policy changes with the abolition of EU milk quotas.     

Intake characteristics of perennial ryegrass varieties when grazed by yearling beef cattle under rotational grazing management

Four intermediate‐heading perennial ryegrass (Lolium perenne L.) varieties, which in previous studies had been associated with high‐ or low‐intake characteristics when swards containing them had been continuously stocked with sheep, were sown as monocultures. They were rotationally grazed, using 1‐d paddocks, with core groups of four yearling Simmental × Holstein beef heifers in 2002 and 2003 and ingestive and ruminative behaviour, and sward factors, were measured. There were two diploid (Belramo and Glen) and one tetraploid (Rosalin) perennial ryegrass varieties and one tetraploid hybrid (Lolium × boucheanum Kunth) (AberExcel) variety. Intake rate (IR) was significantly higher in August 2003 for heifers grazing Glen than those grazing Belramo [27·5 vs. 20·6 g dry matter (DM) min^?1; P = 0·019], but there were no significant differences between varieties in two other measurement periods. This is in contrast to previous results with sheep when IR were significantly higher for Glen than Belramo and for AberExcel than Rosalin. Total jaw movement rates during grazing were significantly higher for heifers on the tetraploid swards than those on the diploid swards (87·7 vs. 83·6 jaw movements min^?1; P = 0·023) in September 2002. Ruminating time was significantly lower for heifers on the tetraploid swards than those on the diploid swards (453 vs. 519 min 24 h^?1; P = 0·012) in July 2002. Digestibility of grass snips was significantly higher on the tetraploid than the diploid swards [697 vs. 680 g digestible organic matter (DOM) kg^?1 DM; P = 0·042] in September 2003 and, within diploids, was significantly higher for Glen than Belramo (696 vs. 663 g DOM kg^?1 DM; P = 0·014). There were significant differences in sheath tube and leaf lengths and in the population density of tillers between and within ploidies, which might have been expected to have influenced intake characteristics, but this was not generally found under rotational grazing with cattle. In order to separate the effects of defoliation interval from those of grazing style of the different ruminant species, it is suggested that grass variety evaluations using continuously stocked cattle swards are required.     

Effects of harvesting perennial ryegrass at different levels of herbage mass on voluntary intake and in vivo digestibility in sheep

The production performance of herbage‐fed animals is affected by herbage voluntary dry‐matter intake (VDMI) and organic matter digestibility. The objective of this study was to determine the effect of herbage mass (HM) on in vivo herbage voluntary intake and digestibility in sheep. The three HM treatments were as follows: 1,100 kg dry matter (DM)/ha (low, L), 2,300 kg DM/ha (medium, M) and 3,700 kg DM/ha (high, H). The study was a Latin square design, repeated on two occasions in 2012: 24 May to 20 July (summer) and 21 July to 5 October (autumn). Twelve Texel wether sheep (individually housed) were offered fresh cut perennial ryegrass herbage for ad libitum consumption. Using the total faecal collection method, the digestibility of dry matter, organic matter, neutral detergent fibre and acid detergent fibre was determined. In summer, L had a similar VDMI to M and both had a higher VDMI than H. In autumn, L had a higher VDMI than both M and H. For dry‐matter digestibility and organic matter digestibility, there was no significant difference between L and M, which were both higher than H. For every 1% increase in neutral detergent fibre digestibility, VDMI increased by 0.03 kg. In the zero‐grazing scenario examined, offering low (1,100 kg DM/ha) HM swards enabled animals to achieve high intakes of highly digestible herbage, which should ensure high animal production performance.     

Fatty acid composition and nutritive value of twelve cultivars of perennial ryegrass

A comparison was made of the fatty acid composition and nutritive value of twelve cultivars of perennial ryegrass ( Lolium perenne L.) differing in heading date and ploidy level. The cultivars were sown in triplicate plots and three sequential cuts of herbage were taken at 20-d intervals during the late spring and early summer to describe the fatty acid composition and other measurements of nutritive value. Differences between cultivars were recorded for DM content ( P  <   0·01) and concentrations of gross energy, neutral-detergent fibre (NDF) and ash ( P  <   0·05). Diploid cultivars had a higher DM content and concentration of NDF ( P  <   0·01) than tetraploid cultivars whilst late-heading date cultivars had the lower NDF ( P  <   0·05), ADF and ash ( P  <   0·01) concentrations. There was variation between cultivars in fatty acid composition. Diploid cultivars had a higher concentration of C18:0 ( P  <   0·01) and C18:1 ( P  <   0·05) than tetraploid cultivars and late-heading date cultivars had the highest concentrations of total fatty acids, C16:0, C18:2 and C18:3 ( P  <   0·05). This was predominantly due to the cultivar Tyrella which is a diploid, late-heading cultivar. The study showed that some variation exists between perennial ryegrass cultivars in concentrations of polyunsaturated fatty acids, which may present opportunities to select for this trait, but further research on the developmental stages and degree of leafiness of cultivars is first required.     

Effect of altering the grazing interval on growth and utilization of grass herbage and performance of dairy cows under rotational grazing

The effects of short grazing intervals in the early part of the grazing season on the growth and utilization of grass herbage, and the performance of grazing dairy cows, in a rotational grazing system were examined. Seventy-six cows were allocated to two grazing treatments: a normal rotation treatment (20-d rotations for the first 60 d) and a short rotation treatment (12-, 8-, 8-, 8-, 12- and 12-day rotations). Thereafter, both treatments had the same grazing interval and over the season as a whole both treatments received the same amount of nitrogen fertilizer and were stocked at the same rate. The short rotation treatment significantly reduced pre- and post-grazing sward heights and pre-grazing herbage mass in May and June. Total herbage production was significantly lower on the short than the normal rotation treatment as a result of a significant reduction in the growth rate of herbage in May and June. The short rotation treatment had a significantly lower milk output per cow. Grazing shorter swards, as a result of shorter rotations, significantly reduced herbage intake, reflecting reductions in intake per bite, grazing time and total bites per day. Treatment had no significant effect on herbage quality or pre- and post-grazing sward height in August and September, despite the increased grazing severity in May and June with the short rotations. The severity of rotation length in this instance had a detrimental impact on animal performance, whereas a more modest reduction in grazing interval may control herbage production, without reducing animal performance.     

Relationships between the yield of perennial ryegrass and of small-leaved white clover under cutting or continuous grazing by sheep

Seven varieties or advanced breeding lines of white clover ( Trifolium repens L.), all of small leaf size, were grown separately in mixtures with perennial ryegrass ( Lolium perenne L.) in an experiment encompassing three harvest years. Harvestable dry-matter (DM) yield measurements were taken of these mixtures and of perennial ryegrass monocultures under two management regimes: cutting and continuous sheep grazing. Considerable differences were observed in the harvestable DM yields of white clover, perennial ryegrass and total yields of the mixtures between plots containing different white clover varieties. White clover yields were generally higher under cutting, and perennial ryegrass yields were higher under grazing. The difference between perennial ryegrass yield in monoculture and in mixture was variable. In the second harvest year, a significant interaction effect was seen between management and white clover variety for white clover yield but not for perennial ryegrass yield. The relationship between clover yield and grass yield differed between the two management regimes. Under cutting, a negative correlation was observed, indicative of competitive effects. However, under grazing, no such correlation was seen. Possible mechanisms underlying these outcomes are discussed.     

Release of cell contents and comminution of particles of perennial ryegrass herbage during ingestion by dairy cows fed indoors or grazing

The effect of feeding indoors fresh perennial ryegrass vs. grazing on ingestive behaviour, release of cell contents and comminution of particles during ingestion, as well as on gas production of ingested boli fermented in vitro, was studied. Indoor feeding and grazing were compared using four dairy cows according to a triple reversal design with six periods. Chemical and morphological composition of the ingested herbage was similar for both indoor feeding and grazing treatments. The intake rate was markedly higher indoors compared with grazing [52·1 vs. 22·9 g dry matter (DM) min^?1] with heavier boli and less saliva added per gram of DM intake. The proportions of intracellular nitrogen and chlorophyll released during mastication after ingestion of herbage fed indoors were lower, and the median size of the particles in the boli was larger (5·97 vs. 4·44 mm) compared with grazing. As a result, the rate of gas production in vitro was also lower for herbage fed indoors compared with grazing (0·423 vs. 0·469 mL min^?1 g^?1 incubated DM). Indoor feeding or grazing may have limited consequences in vivo on the kinetics of availability of nutrients for micro‐organisms in the rumen, because the consequences of the more extensive physical damage suffered by herbage ingested at grazing could be compensated by a lower intake rate.     

Differences in the nitrogen use efficiency of perennial ryegrass varieties under simulated rotational grazing and their effects on nitrogen recovery and herbage nitrogen content

Eight varieties of perennial ryegrass (six new varieties and two old ones) grown at five levels of applied fertilizer (100, 200, 300, 400 and 500 kg of N ha^–1) were cut monthly during two growing seasons (March to October in 1997 and 1998) and their herbage dry‐matter (DM) yield and nitrogen (N) content were determined. Herbage leaf content and the N content of young fully expanded leaves were also measured in 1997, and monthly recovery of applied N was determined in both the first and second harvest years by using ¹⁵N. The rank order of varieties was similar for annual yield of DM and N at all five fertilizer levels. Proportional differences between varieties in DM yield were greatest in the first cut of each year, the late‐heading candidate variety Ba12151 out‐yielding the old late‐heading variety S23 by more than 70%. However, differences in annual DM yield were much more modest than in early spring yield, up to 10% in 1997 and up to 21% in 1998. The relatively small differences in total annual DM yield were attributed to only a small proportion of the applied N being recovered during a single regrowth period, most of the remainder becoming available for uptake in subsequent regrowth periods. There were small but highly statistically significant differences among varieties in the N content of their leaves, leaf N content being inversely related to yield of DM and N. This lends further support to the hypothesis that the metabolic cost of protein synthesis and turnover is a key factor controlling genetic variation both in leaf yield and in annual DM and N yield under frequent harvesting. Seasonal variation in herbage N content was much greater than differences among varieties in mean N content over all harvests. In May of both years at all applied fertilizer levels, herbage N content fell below the 20 g N kg^–1 DM level required by productive grazing animals.     

Effects of grazing and precipitation on herbage production,herbage nutritive value and performance of sheep in continental steppe

The present study highlights the effects of sheep grazing and precipitation on herbage and animal performance in a grazed steppe of Inner Mongolia. Experimental data were collected during grazing periods of four consecutive years (2005–2008), and effects were analysed across a gradient of seven grazing intensities. Variation in annual precipitation, reflected by the effect of ‘year’, was the major factor affecting herbage; i.e., the production and nutritive value of herbage increased with increasing precipitation. Herbage parameters were also affected by grazing intensity, as herbage production (HP) and herbage nutritive yields decreased, while herbage nutritive values increased with increasing grazing intensity. The grazing‐induced decrease in herbage nutritive yields suggests that decreases in HP offset the positive effect of grazing on the nutritive value. Liveweight gain (LWG) was predominantly affected by grazing intensity, as LWG per sheep and per ha decreased and increased, respectively, with increasing grazing intensity. However, responses varied among years: LWG per sheep was maximized by light grazing in the drought year and by moderate grazing the wet year. Our results showed that herbage shortage at high grazing intensities reduces LWG per sheep and thus diminishes responses in LWG per ha. Nevertheless, the highest grazing intensity provides highest animal production per ha in the short term; however, this is not sustainable in the mid‐ and long term because decreasing HP induces degradation processes. Based on our results, a reduction in grazing intensity that still provides 78% of the maximum LWG per ha meets the requirements of a sustainable grazing management.     

Effects of grazing by sheep or cattle on sward structure and subsequent performance of weaned lambs

The study was designed to test the hypothesis that grazing management in early season could alter sward structure to facilitate greater animal performance during critical periods. The effects of grazing a mixed perennial ryegrass/white clover sward at different sward surface heights, by cattle or sheep, in early season on sward composition and structure, and on the performance of weaned lambs when they subsequently grazed these swards in late season were determined. In two consecutive years, from mid‐May until mid‐July, replicate plots (three plots per treatment) were grazed by either suckler cows and calves or ewes and lambs at 4 or 8 cm sward surface heights (Phase 1). From mid‐August (Year 1) or early August (Year 2), weaned lambs continuously grazed, for a period of 36 d (Year 1) or 43 d (Year 2) (Phase 2), the same swards maintained at 4 cm (treatment 4–4), 8 cm (treatment 8–8) or swards which had been allowed to increase from 4 to 8 cm (treatment 4–8). Grazing by both cattle and sheep at a sward surface height of 4 cm compared with 8 cm in Phase 1 resulted in a higher (P < 0·001) number of vegetative grass tillers per m² in Phase 2, although the effect was more pronounced after grazing by sheep. Sheep grazing at 8 cm in Phase 1 produced a higher number of reproductive tillers per m² and a greater mass of reproductive stem (P < 0·001) than the other treatment combinations. The mass of white clover lamina was higher under cattle grazing (P < 0·05), especially on the 8‐cm treatment, and white clover accounted for a greater proportion of the herbage mass. These effects had mainly disappeared by the end of Phase 2. On the 4–4 and 8–8 sward height treatments the liveweight gain of the weaned lambs was higher (P < 0·05) on the swards previously grazed by cattle than those grazed by sheep. The proportion of white clover in the diet and the herbage intake also tended to be higher when the weaned lambs followed cattle. However, there was no difference in liveweight gain, proportion of white clover in the diet or herbage intake between swards previously grazed by cattle or sheep on the 4–8 sward height treatment. It is concluded that grazing grass/white clover swards by cattle compared with sheep for the first half of the grazing season resulted in less reproductive grass stem and a slightly higher white clover content in the sward, but these effects are transient and disappear from the sward by the end of the grazing season. They can also be eliminated by a short period of rest from grazing in mid‐season. Nevertheless these changes in sward structure can increase the performance of weaned lambs when they graze these swards in late season.     

Production performance and meat quality of grazing lambs finished on red clover, lucerne or perennial ryegrass swards

The combined benefits of a high crude protein concentration, and possible protein protection and growth‐promoting properties, make forage legumes potentially attractive as a natural means of increasing liveweight gain and time to slaughter of lambs in lamb finishing systems. An experiment was conducted to compare the production performance and meat quality of grazing lambs finished on red clover (Trifolium pratense), lucerne (Medicago sativa) or perennial ryegrass (Lolium perenne) swards. Replicate (n = 2) swards of red clover, lucerne and perennial ryegrass were rotationally grazed by ten ram lambs and ten ewe lambs from weaning until selection for slaughter at UK fat class 3L. Lambs grazing the red clover sward had a significantly higher liveweight gain and required significantly fewer days to slaughter than lambs grazing the lucerne sward (305 g d^?1 vs. 243 g d^?1; 38 d vs. 50 d), which in turn had a higher liveweight gain and required fewer days to slaughter than lambs grazing the perennial ryegrass sward (184 g d^?1; 66 d). Lambs grazing the red clover and lucerne swards had significantly higher herbage intakes than those grazing the perennial ryegrass sward (2·06, 1·72 and 1·16 kg DM d^?1 respectively), but in vivo digestibility of herbage was similar. Lambs grazing the red clover and lucerne swards also had significantly higher serum urea concentrations than those grazing ryegrass (12·5, 11·1 and 6·2 mmol L^?1 respectively). Killing‐out percentage was significantly higher for lambs grazing the red clover sward than for lambs grazing the perennial ryegrass sward (48% vs. 46%). There were no significant effects of finishing system on meat flavour, but meat from lambs finished on the lucerne sward was oxidatively less stable than that from lambs finished on the perennial ryegrass sward. Grazing the forage legume swards significantly increased the proportion of linoleic and linolenic acid in muscle tissue, and therefore the proportion of unsaturated to saturated fatty acids (0·19, 0·16 and 0·12 for the red clover, lucerne and perennial ryegrass swards respectively). However, the n?6/n?3 ratio was significantly lower for the muscle of lambs grazing the perennial ryegrass sward compared with those grazing the forage legume swards (1·13, 1·08 and 0·98 for the red clover, lucerne and perennial ryegrass swards respectively). The results indicate that by grazing lambs on forage legume swards it is possible to increase individual lamb performance without compromising meat quality.     

Identifying causes of low persistence of perennial ryegrass (Lolium perenne) dairy pasture using the Basic Grassland model (BASGRA)

Recent years have seen a decline in herbage production and tiller populations in New Zealand's perennial ryegrass (Lolium perenne) dairy pastures. One hypothesis is that modern genotypes are less suited to the warmer, drier weather experienced under changing climate patterns. In this study, a combination of long-term trial data (2011–2017) and a process-based pasture model (BASGRA) was used to explore the causes and possible mitigation of the observed production and population loss at three sites (dryland sites in Northland and Waikato and an irrigated site in Canterbury). Bayesian calibration was used to identify the model parameter sets that were consistent with the trial data and to identify differences in plant morphology and responses between sites. The model successfully simulated the observed differences in tiller numbers between the dryland sites, where populations and production declined rapidly after the second year and the irrigated site where populations and production were maintained. Analysis of the model calibrations along with preliminary scenario simulations suggests that increased tiller mortality associated with drought was the main cause of persistence failure at the dryland sites and that decreasing grazing pressure or breeding for tolerance to higher temperatures may not be successful in preventing this.     

Effects of livestock breed and grazing intensity on biodiversity and production in grazing systems. 1. Nutritive value of herbage and livestock performance

Reduction of grazing intensity and the use of traditional instead of commercial breeds has frequently been recommended to meet biodiversity and production goals in sustainable grazing systems in Europe. To test the impact of such practices across a range of contrasting grassland types, integrated measurements of foraging behaviour, agronomic production and botanical, structural and invertebrate biodiversity were made over three years on four sites in the UK, Germany, France and Italy. The sites in the UK and Germany were mesotrophic grassland with high productivity and low to moderate initial levels of plant diversity, and were grazed by cattle. The French site was a semi‐natural, species‐rich grassland grazed by cattle. The Italian site contained a wider range in plant diversity, from species‐rich to mesotrophic grassland, and was grazed by sheep. The treatments were: MC, moderate grazing intensity with a commercial breed – this was designed to utilize herbage growth for optimum livestock production; LC, lenient grazing intensity with a commercial breed – this was designed to increase biodiversity by not fully utilizing herbage growth; and LT, lenient grazing intensity with a traditional breed – this was also designed to increase biodiversity. Neither fertilizers nor pesticides were applied. The nutritive value of the herbage and the performance of the livestock were measured. Mean stocking rates were proportionately 0·30–0·40 lower and mean sward heights and herbage mass on offer were 0·30–0·50 higher on the LC and LT treatments compared with the MC treatment. The proportion of live and dead material, and leaves and stems in the herbage, its chemical composition and nutritive value were little affected by the treatments. Individual livestock performance, measured as liveweight gain, showed no consistent response to treatment. In Germany, performance on the MC treatment was slightly lower than on the LC and LT treatments but no such difference was found on the sites in the other countries. Livestock breed did not have a strong effect on livestock performance. In the UK and France the traditional breeds had a lower performance but this was not the case in Germany or Italy. Livestock performance per ha of the LC and LT treatments was up to 0·40 lower than of the MC treatment. It is concluded that biodiversity‐targeted extensive grazing systems have potential to be integrated into intensive livestock production systems because the individual livestock performance reaches a similar level compared to a moderate grazing intensity. Traditional breeds did not have a production advantage over commercial breeds on extensively managed pastures.     

A comparison between cutting and animal grazing for dry‐matter yield,quality and tiller density of perennial ryegrass cultivars

Perennial ryegrass (Lolium perenne L.) evaluation trials are often conducted under simulated grazing to identify the most productive cultivars. It is unclear whether simulated grazing identifies the most productive cultivar for animal‐grazed swards. Ten cultivars were established as plots and managed concurrently under simulated grazing (SG), animal grazing (AG) and conservation (CON). The experiment lasted 3 years with dry‐matter (DM) off‐take, digestibility, tiller density and ground‐cover score recorded in all years. A good relationship existed between DM off‐take under SG and CON (R² = 0·73). The relationship between SG and AG was strongest in year 2 and 3 (R² = 0·53 and 0·55 respectively). High DM production was observed in SG swards in year 1; this was weakly related to the DM production of the AG sward. Across the 3 years, the CON treatment had higher yields than either of the other two treatments and was poorly correlated to DM yield under AG, confirming that cultivars should be evaluated under a similar defoliation frequency to their intended use. Tiller density declined quickest under CON and slowest under AG. Some reranking of cultivars occurred between defoliation managements. The results show that simulated grazing is a useful indicator of DM yield performance of animal‐grazed swards.     

Morphology and nutritive value of perennial ryegrass cultivars at different phenological stages

Eight perennial ryegrass cultivars (representing the variations in ploidy, heading date and water‐soluble carbohydrates concentration) were investigated for morphology and nutritive value at three phenological stages: pre‐heading vegetative, reproductive and post‐flowering vegetative stages. Chemical compositions and digestibility of morphological components (lamina, pseudostem and reproductive stem) from each perennial ryegrass cultivar were analysed in a split‐plot design. At the vegetative stages, perennial ryegrass cultivars differed significantly in the proportions of lamina and pseudostem. Tetraploid cultivars, Base and Bealey, always had the greatest lamina proportion (51.8% and 53.2% at the pre‐heading and post‐flowering vegetative stages respectively). At the reproductive stage, the emergence of seed heads diminished the differences in morphology among cultivars. Perennial ryegrass cultivars also had distinct nutritive value throughout three phenological stages. The high‐sugar cultivar, AberMagic, had high WSC concentrations (276, 227 and 90 g/kg DM at the pre‐heading vegetative, reproductive and post‐flowering vegetative stages respectively); the intermediate‐heading cultivars, Kamo and Commando, generally had a lower organic matter digestibility in dry matter than the late‐heading cultivars at the pre‐heading vegetative (70.7% vs. 74.4%) and reproductive stage (63.9% vs. 68.2%). However, although the morphological components were different in nutritive value consistently, the differences in morphology did not account for the variation in nutritive value among perennial ryegrass cultivars.     

Effect of a stay-green locus on the dry-matter yield, nitrogen yield and shoot density of perennial ryegrass

A rare stay‐green allele transferred from meadow fescue (Festuca pratensis L.) to perennial ryegrass (Lolium perenne L.) has improved both the colour of turf and the nutritive value of herbage. In this study its effect on shoot density and forage yield was assessed. Equivalent populations of perennial ryegrass were constructed with and without the stay‐green allele, following eight generations of backcrossing to perennial ryegrass. The stay‐green population, the normal population and the cv. AberStar were compared over two harvest years (2005 and 2006) in a field experiment with six application rates of N fertilizer (100, 200, 300, 400, 500 and 600 kg ha^?1 annually). There were no significant interactions between level of N fertilizer and population in any of the traits measured. The mean annual dry‐matter (DM) yield over all populations and fertilizer levels was 6·45 t ha^?1 lower in the second harvest year. Mean annual DM yields over all fertilizer levels of the normal population were higher than, or equal to, AberStar while those of the stay‐green population were significantly (proportionately 0·10–0·13) lower than the normal population. In 2005, the mean total yield of N in the herbage of the stay‐green population was 0·09 lower than that of the normal population and the mean concentration of N over all harvests was 1·5 g kg^?1 DM higher. The shoot density of the stay‐green population after the last harvest in November 2006 was 0·18 lower than that of the normal population (3689 and 4478 shoots m^?2 respectively).     

Possibilities of increasing the residual water‐soluble carbohydrate concentration and aerobic stability of low dry‐matter perennial ryegrass silage through additive and cultivar use

Increasing the residual water‐soluble carbohydrate (WSC) concentration in silage may improve the nutritional value but impair aerobic stability. Our aim was to determine whether the residual WSC concentration and aerobic stability of low dry‐matter (<135 g kg^?1) perennial ryegrass silage could be manipulated through the judicious use of additive and cultivar. Seven additive treatments, including three innovative treatments, were compared across four consecutive harvests of the cultivars AberDart (bred to accumulate high concentrations of herbage WSC) and Fennema (control). The standard of fermentation of silage ensiled without additive (untreated) ranged from very bad to excellent. Application of ammonium tetraformate, at 3 and 6 L t^?1, or homofermentative lactic acid bacteria (LAB) alone had an inconsistent effect on the fermentation and aerobic stability, and negligible effect on residual WSC concentration. A mixture of Lactobacillus buchneri and homofermentative LAB was not an effective silage additive, producing generally poorly fermented silage. An antimicrobial mixture of sodium benzoate, sodium propionate, sodium nitrite and hexamethylenetetramine, applied at 2·5 and 5 L t^?1, frequently improved the standard of fermentation, but the effects were subject to the application rate. The high application rate was the most effective additive evaluated at improving the fermentation and increasing residual WSC concentration and consistently produced silage of excellent standard of fermentation. However, the antimicrobial mixture was not effective at protecting against aerobic instability. The effects of additive treatment were largely inconsistent across cultivars. Overall, AberDart had a negligible effect on the silage fermentation, residual WSC concentration and aerobic stability compared with Fennema.