Grassland research priorities: Ideas for the future

Abstract

Four levels of available dry matter (DM) were maintained on a continuously grazed irrigated Midmar Italian ryegrass (Lolium multiflorum Lam.) pasture by means of a “put‐and‐take” grazing procedure. The pasture was stocked with three successive sets of weaned lambs in winter, spring and early summer respectively. The relation between average daily gains (ADG) and available DM was positively linear At equivalent levels of available DM, gains were greater in spring than in either the winter and summer periods (P ≤0,01), but there were no differences in gains between winter and summer. There was a negative linear relation between average stocking rate (the rate required to achieve a given level of herbage availability) and available DM. Stocking rates in spring and summer were not significantly different, but both were higher (P≤0,01) than those in winter. Within the range of the differential treatments applied, relations between stocking rate and ADG were negatively linear, and there was an interactive effect (P≤0,01) between stocking rate and grazing period. Changes in ADG with a unit change in stocking rate were greatest in winter, intermediate in summer and least in spring. Gains/ha were curvilinearly related to available DM. The curves indicate that the amounts of available DM required for maximum gains/ha were least in spring, intermediate in summer and greatest in winter.

From a serial cutting trial conducted concurrently with the grazing, a growth rate curve was developed for Midmar ryegrass. This curve had two maxima, with the maximum growth rate in spring being more than double that in autumn. The in vitro digestible organic matter content and crude protein content decreased from 80,6% and 24,1% in autumn to 63,1% and 10,6%, respectively, in summer. Crude fibre content increased from 10,1 % in autumn to 30,1 % in summer.     

Relationship of rumen fill and fermentation to diurnal and seasonal variation of herbage intake in dairy cows grazed on perennial ryegrass pasture

To clarify the effect of digesta weight in the reticulorumen on diurnal and seasonal fluctuations in herbage intake, six ruminally cannulated, non‐lactating dairy cows were grazed on perennial ryegrass/white clover pasture during morning and evening sessions in spring and autumn. The digesta weight of fresh matter, dry matter (DM) and fiber in the reticulorumen at the beginning and the end of each grazing session was lower in spring than in autumn (P < 0.01). Although the digesta weight was similar between the sessions at the beginning of grazing, it was greater for the evening than for the morning at the end of grazing (P < 0.01). The large particles proportion in the digesta was lower for the morning than the evening (P < 0.01), and it was lower in spring than in autumn (P < 0.01). The concentrations of volatile fatty acids in rumen fluid were generally higher in spring compared with autumn. The herbage DM intake during the evening was greater compared with the morning in both seasons (P < 0.01). However, there was no difference in herbage DM intake between seasons. The results showed that the rumen digesta fill was not the sole factor explaining diurnal and seasonal variation of herbage intake in grazing dairy cows.     

不同放牧强度对多年生黑麦草—白三叶草地群体密度的影响

在中、高放牧强下黑麦草分蘖密度略有下降，而在低放牧强度下则有所上升。白三叶枝条密度受放牧强度影响较小。秋季的重牧使黑麦草分蘖密度极显著下降（P＜0．01）。6月份随着放牧强度的增强黑麦草案死亡数显著减少（P＜0．05），草地群体密度亦随之减少（P＜0.05）。在秋季随着放牧强度的增大黑麦草单蘖重明显减少（P＜0．05）。黑麦草和白三叶的单菜（枝）重与其密度均呈强负相关（P＜0．01）。白三叶的单枝重与生物量呈正相关（P＜0．05）。以上分析表明，中等放牧强度（70％利用率）有利于保持合理的草地群体密度和较高的生物量。     

不同放牧制度和强度下奶牛生产性能的研究──1.放牧对牧草采食量及营养摄入量的影响

本文作者在湖南南山牧场研究了两种放牧制度（分区轮牧和连续放牧）和三种放牧强度（0．467，0．667和0．867ha／头）对处于泌乳中后期的黑白花奶牛在多年生黑麦草／由三叶人工草地上的放牧来食量、采食植物组成、营养摄入量的影响。结果表明：轮牧制奶牛的采食量低于连续放牧制，但其口粮组成中黑麦草和白三叶的比例高于连续放牧，故粗蛋白质、总能、钙和磷的日摄入量也低于轮牧制奶牛。随放牧强度的增加，奶牛的来食量、以及粗蛋白质、酸性洗涤纤维、总能、钙和磷的摄入量均有所增加，但三种放牧强度间差异并不显著。放牧强度越大，家畜日粮组成中黑麦草和白三叶的比例越大，而枯草和杂草所占比例越小。这说明在南山试验条件下，放牧制度和放牧强度对奶牛的采食量及各种营养物质的日摄入量有一定影响。     

Herbage intake and ruminal digestion of dairy cows grazed on perennial ryegrass pasture either in the morning or evening

This study aimed to clarify diurnal fluctuations of herbage intake, ruminal fermentation of herbage carbohydrates and proteins, and digesta particulate weight in the rumen of grazing dairy cows. Six ruminally cannulated, non‐lactating dairy cows were grazed on perennial ryegrass/white clover pasture either in the morning (04.00 to 08.00 hours) or the evening (16.00 to 20.00 hours). Cows grazed in the evening spent more time (P < 0.01) and consumed more herbage (P < 0.01) compared with cows grazed in the morning. Higher (P < 0.05) daily mean concentrations of total volatile fatty acid, propionate and n‐butyrate in rumen fluid were observed for cows grazed in the evening compared with cows grazed in the morning. Although cows grazed in the evening ingested more crude protein compared with cows grazed in the morning, no significant difference in NH₃‐N concentration in rumen fluid was observed between them. The ratio of purine‐derivative concentration to creatinine concentrations was higher (P < 0.01) in the urine of cows grazed in the evening than in cows grazed in the morning. These results clearly indicated that evening grazing was advantageous for dairy cows compared with morning grazing, in terms of ruminal fermentable energy intake and nitrogen utilization efficiency.     

不同放牧制度下多年生黑麦草/白三叶人工草地叶组织转化的研究

本研究应用组织转化的理论和方法,通过放牧试验对湖南南山牧场多年生黑麦草/白三叶人工草地叶组织转化进行了较为系统的研究。主要研究内容有:采用连续放牧(2亩/只绵羊)、间断放牧Ⅰ(2亩/只绵羊)和间断放牧Ⅱ(1亩/只绵羊)三个放牧处理,分析三者之间的叶组织转化情况。研究结果表明:连续放牧、间断放牧Ⅰ和间断放牧Ⅱ之间的多年生黑麦草叶片组织净生产率无显著差异,而白三叶叶组织的净生产率却以连续放牧处理较高,为11.44公斤/公顷/天,间断放牧Ⅰ和间断放牧Ⅱ之间无显著差异;三个放牧处理的多年生黑麦草与白三叶叶组织总净生产率之间无显著差异。     

Responses of Italian ryegrass to phosphorus on highly‐weathered soils

Italian ryegrass (Loliwn multiflorum cv. Midmar) responses to fertilizer P were studied in field experiments under irrigation on highly‐weathered ferrallitic soils at two localities in Natal. Each experiment was conducted over two seasons (1985 and 1986), the pasture being re‐established after the first season. Large dry matter yield responses to P were measured on both soils. Phosphorus effects were greatest during the establishment phase (autumn) and, on the colder site, in spring. Concentrations of P in herbage were much lower in winter than in autumn or summer. The greater responsiveness to P in spring and the lower P concentrations in herbage during the colder months suggested that restricted P uptake contributed to yield reductions in winter. Relationships between ryegrass P concentrations and yield indicated substantial within‐season variations in internal P requirement for maximum yield. This detracts from the usefulness of routine herbage P analyses for assessing ryegrass P sufficiency. However, soil analysis using an alkaline extractant (NH₄HCO₃/EDTA/NH₄F at pH 8.0), showed promise for predicting responsiveness to P. Concentrations of P in Italian ryegrass were well below the requirements reported in the literature for most classes of grazing ruminants, particularly during the colder months.     

奶牛放牧对北方农牧交错带人工草地植被的影响

研究了不同处理奶牛放牧对混播人工草地植被的影响。结果表明,牧草现存量随着放牧强度的增加而降低,轻牧比中牧高7.28%,且轮牧高于连续放牧1.99%,轮牧对紫花苜蓿和无芒雀麦的再生有利。随放牧强度增加,紫花苜蓿和无芒雀麦重要值下降,蓝茎冰草和新麦草增加。放牧对牧草的茎叶比有显著影响,放牧后4种牧草的茎叶比均有下降,连续放牧高于轮牧。根系主要集中在土壤表层0~10 cm,约占0~30 cm总量的70%,且其生物量也以轮牧制较高,随放牧强度的增加而下降。     

The effect of glyphosate, paraquat and paclobutrazol on lolitrem B levels in endophyte-infected perennial ryegrass

Two herbicides (glyphosate and paraquat) and a plant growth regulator (paclobutrazol) were applied to endophyteinfected (Acremonium lolii) perennial ryegrass swards. Subsamples of these swards were then chemically analysed at intervals up to 28 days later for lolitrem B, the compound responsible for perennial ryegrass staggers in domestic livestock. Glyphosate and paclobutrazol had no effect on lolitrem B concentrations. Paraquat applications decreased lolitrem B concentrations in the herbage. Because none of the chemicals tested increased the concentration of lolitrem B in the herbage, they are unlikely to be directly implicated in perennial ryegrass staggers in grazing animals.     

Kikuyu over-sown with ryegrass and clover: dry matter production,botanical composition and nutritional value

The seasonality of growth and low nutritional value of kikuyu (Pennisetum clandestinum) pasture restrict milk production. The aim of the study was to determine the dry matter yield, botanical composition and nutritional value of irrigated kikuyu over-sown with annual ryegrass (Lolium multiflorum var. westerwoldicum), white clover (Trifolium repens) and red clover (T. pratense) or a mixture of perennial ryegrass (Lolium perenne) with white and red clovers under intensive grazing conditions with dairy cows. The incorporation of annual ryegrass, perennial clover or perennial ryegrass–clover into kikuyu pasture changed the seasonal fodder flow and increased the spring dry matter (DM) production. The over-sowing of kikuyu with annual ryegrass had no effect on the DM production of kikuyu during the summer and autumn. Kikuyu and kikuyu–ryegrass, fertilised with nitrogen fertiliser, had a higher DM production rate than kikuyu–clover pastures. Kikuyu–ryegrass pasture transformed from ryegrass-dominant in spring to kikuyu-dominant in summer and only kikuyu in autumn. This led to a decrease in metabolisable energy (ME) and increase in neutral detergent fibre (NDF) content of the pasture during spring, summer and autumn as kikuyu became more dominant. The clover content of kikuyu over-sown with clover decreased annually but was still higher than 30% at the end of two years after establishment. As the kikuyu content of the kikuyu–clover pastures increased, the seasonal growth rate changed from a low autumn growth (37.9 kg DM ha^?1 d^?1) in the first year to a higher autumn growth (48.5 kg DM ha^?1 d^?1) in the second year. The over-sowing of kikuyu with clover resulted in lower DM production and NDF values and higher crude protein (CP), ME and calcium (Ca) values. The lowest CP content in kikuyu–ryegrass pasture was during summer and autumn when kikuyu was dominant. The Ca content of the grass pastures (kikuyu and kikuyu–ryegrass) was low. The phosphorus (P) content of both the kikuyu–clover and grass pastures exceeded the requirement needed for dairy production (0.38%). The mean Ca:P ratio of the kikuyu–clover pasture meets the 1.6:1 ratio needed by dairy cows. The kikuyu and kikuyu–ryegrass pasture had a Ca:P ratio lower than 1:1 and Ca supplementation would be needed for dairy cows. The incorporation of annual ryegrass, perennial clover or perennial ryegrass–clover into kikuyu pasture improved the seasonal DM production and nutritional value of the pasture.     

Influence of grazing frequency and intensity on aerial and reproductive tillering in Lolium perenne L. under subtropical conditions

Abstract

Reproductive and aerial tillering dynamics in Lolium perenne L. (perennial ryegrass) was monitored for two years under grazing. Reproductive tillers were observed from winter (June) to midsummer (February) with the main period of initiation occurring in spring to early summer (August to October). For infrequent lenient grazing, reproductive tiller densities ranged from 102 (July 1993) to 1 900 (September 1993) tillers m^?2, and from 29 (June 1994) to 980 (September 1994) tillers m^?2. By contrast, simulated continuous grazing (CG) resulted in reproductive tiller densities ranging from 13 (August 1993) to 100 (October 1993) tillers m^?2, and from 25 (July 1994) to 46 (September 1994) tillers m^?2. Aerial tillers were initiated mainly during spring, and to a lesser extent autumn and winter, with no appreciable number being recorded during summer. For infrequent lenient grazing, aerial tiller densities ranged from 25 (February 1993) to 1 620 (September 1993) tillers m^?2, and from 362 (August 1994) to 1 524 (September 1994) tillers m^?2. By contrast, CG resulted in aerial tiller densities ranging from 123 (May 1993) to 14 (June 1993) tillers m^?2, and from 5 (July 1994) to 29 (May 1994) tillers m^?2. There was no indication that reproductive or aerial tillers contribute to the persistence of perennial ryegrass under the grazing frequencies and intensities tested.     

高寒山区白三叶／多年生黑麦草放牧草地植物组分季节动态研究

将高寒山区白三叶／多年生黑麦草放牧草地植物组分分成白三叶、多年生黑麦草、单子叶杂草、阔叶杂草和死物质5种进行季节动态研究，进而对该草地牧草季节供给质量进行评价，找出生产管理上的不足并加以改进。该草地多年生黑麦草占据绝对优势，但豆科牧草含量不足；冬春季节死物质含量过高，夏秋季节利用强度不足。草地供给的牧草质量9月最高，播种牧草含量达79．90％，12月最差为44．68％；而可利用牧草含量最高为8月的97．04％，12月最低为45．55％。     

The evaluation of endophyte toxin residues in sheep fat

Abstract

AIM: To monitor changes in concentrations of lolitrem B and epoxy-janthitrems in the fat of sheep grazing perennial ryegrass infected with wild-type- and AR37-endophyte, respectively, during the time of year when ryegrass staggers would be expected to be observed.

METHODS: Ten 5-month-old lambs with no previous exposure to endophytes were grazed on either wild-type (containing lolitrem B, n = 5) or AR37 (containing epoxy-janthitrems, n = 5) endophyte-infected perennial ryegrass (Lolium perenne L.) pastures between October 2008 and June 2009. Animals were regularly assessed for ryegrass staggers using the Keogh scale (0 = no signs, 5 = severe tremors). When a score of > 3.5 was observed animals were removed from the treatment pastures for 1 month. Fat biopsy samples were taken from each animal at approximately monthly intervals and analysed for endophyte metabolites using high performance liquid chromatography (HPLC) methods developed during this study. Regular herbage samples were also taken and concentrations of endophyte metabolites measured.

RESULTS: Efficient and reproducible methods to analyse both lolitrem B and epoxy-janthitrems in fat were developed. Concentrations of lolitrem B and epoxy-janthitrems in herbage and in sheep fat increased from late November to peak in mid-February. Ryegrass staggers was observed in both groups of sheep at this time. Following 1 month of grazing non-infected pasture mean concentrations in fat of lolitrem B decreased by 43% from 61.8 to 35.3 ppb, and of epoxy-janthitrems by 38% from 1032.0 to 639.5 ppb. Maximum concentrations in herbage of epoxy-janthitrems (35.7 ppm) were higher than of lolitrem B (3.4 ppm), but signs of staggers were less severe in sheep grazing pasture containing the former compared with the latter (median Keogh scores in late February were 2 and 3, respectively), consistent with epoxy-janthitrems being low potency toxins.

CONCLUSION: This study demonstrated that concentrations of epoxy-janthitrems and lolitrem B in sheep fat increased quickly during the initial phase of the study when concentrations in pasture increased, and decreased when animals were removed from pastures containing these compounds. These data will be used in the risk assessment of the endophyte metabolites.     

人工草地杂草生态学研究Ⅰ杂草入侵与放牧强度之间的关系

本文分析了白三叶草十多年生黑麦草混播人工草地上杂草入侵与放牧强度之间的关系，得出如下初步结论：１）杂草入侵的种数主要决定于放牧强度；２）α物种多样性随放牧加重而有增－减－增的趋势；３）入侵的主要杂草种为点腺过路黄等８个种；４）所论人工草地都处在恢复演替的先锋阶段，因而草地退化的进程还是能予以遏制的。     

Dietary selection of sheep grazing the semi‐arid grasslands of Inner Mongolia,China at different grazing intensities

The objective of this study was to investigate dietary selection of sheep grazing semi‐arid grassland in Inner Mongolia, China, using the difference in organic matter digestibility (OMD) of herbage ingested and herbage on offer as indicator for selection. Faecal N was used as digestibility index for herbage ingested (FOMD), while OMD of herbage on offer (GOMD) was estimated from gas production obtained by the Hohenheim gas test. It was hypothesized that the difference between FOMD and GOMD is high, when grazing animals select against low quality herbage provided that herbage is abundant. In a grazing experiment, six grazing intensities (1.5, 3.0, 4.5, 6.0, 7.5 and 9.0 sheep/ha), representing light to very heavy grazing intensity for the semi‐arid grassland, were compared. The amount of herbage on offer decreased with increasing grazing intensity. Independent statistical analysis of FOMD and GOMD showed that the differences between grazing intensities for both OMD determinations (FOMD: 54.0–57.3%, GOMD: 55.2–57.5%) were not significant (p > 0.05). The difference between FOMD and GOMD was not significant for grazing intensities, but varied between sampling periods from ?4 to 1 percentage units. In conclusion, the lack of significance for the difference between FOMD and GOMD suggests that for the semi‐arid grassland of Inner Mongolia, China, sheep did not select their feed due to a homogeneous nutritional composition of herbage on offer in 2005, regardless of grazing intensity.     

Effect of timing and type of supplementary grain on herbage intake,nitrogen utilization and milk production in dairy cows grazed on perennial ryegrass pasture from evening to morning

The present study aimed to clarify the effect of timing and type of supplementary grain in grazing dairy cows on herbage dry matter intake (HDMI), nitrogen utilization and milk production. Eight lactating cows were allowed to graze from evening to morning during three seasonal periods (spring, summer, autumn). They were randomly allocated to four treatments (timing: pre‐ (Pre) or post‐grazing (Post), for large grain allotments consisting of 75% of daily grain offered; grain type: barley or corn) in 4 × 4 Latin square designs in each period. In the spring period, HDMI was greater for cows fed corn than those fed barley (P = 0.005), whereas cows in the Pre treatment had a similar HDMI, higher (P = 0.049) urinary purine derivative concentration and greater (P = 0.004) milk yield compared with cows in the Post treatment. In the summer and autumn periods, timing treatments did not affect HDMI, nitrogen utilization or milk production, but cows supplemented with barley had higher urinary purine derivatives concentration (P < 0.05) and milk yield (P < 0.05) compared with those supplemented with corn. The results indicate that large grain allotments immediately before evening grazing during early grazing seasons increased ruminal microbial protein synthesis and milk production without reducing HDMI regardless of grain type.     

Response of lambs to continuous and rotational grazing at four grazing intensities on Midmar Italian ryegrass

Abstract

Irrigated Midmar Italian ryegrass (Lolium multiflorum Lam.) was grazed either continuously or rotationally at four grazing intensities by three successive sets of weaned lambs for the winter, spring and summer periods, respectively. The “put‐and‐take” system was applied. In the case of continuous grazing, amounts of available dry matter (DM) per hectare were varied, whereas with rotational grazing different grazing intensities were established by allocating different amounts of DM per unit livemass. Amounts of DM on offer were determined in both systems to provide a basis for comparison.

There were no differences in average daily gain (ADG) at equivalent levels of available DM between grazing procedures in winter. In both spring and summer, however, ADG at given levels of available DM was greater (P ≤0,01) with continuous than with rotational grazing. Stocking rate at equivalent levels of available DM was higher (P ≤0,01) for rotational as compared with continuous grazing in winter and summer, but in summer, grazing procedure had no effect on stocking rate. There was an interaction between stocking rate and grazing method in winter (P ≤0,01). At high stocking rates, ADG were higher (P ≤0,01) under rotational than under continuous grazing. In spring and summer the ADG for continuous grazing was higher (P ≤0,01) than that for rotational grazing at equivalent stocking rates. The estimated stocking rates for maximum gains/ha ranged in the different seasons from 45 to 123 lambs/ha.     

Herbage intake of dairy cows in mixed sequential grazing with breeding ewes as followers

This study aimed to evaluate the hypothesis that mixed sequential grazing of dairy cows and breeding ewes is beneficial. During the seasons of spring–summer 2013 and autumn–winter 2013–2014, 12 (spring–summer) and 16 (autumn–winter) Holstein Friesian cows and 24 gestating (spring–summer) and lactating (autumn–winter) Pelibuey ewes grazed on six (spring–summer) and nine (autumn–winter) paddocks of alfalfa and orchard grass mixed pastures. The treatments “single species cow grazing” (CowG) and “mixed sequential grazing with ewes as followers of cows” (MixG) were evaluated, under a completely randomized design with two replicates per paddock. Herbage mass on offer (HO) and residual herbage mass (RH) were estimated by cutting samples. The estimate of herbage intake (HI) of cows was based on the use of internal and external markers; the apparent HI of ewes was calculated as the difference between HO (RH of cows) and RH. Even though HO was higher in CowG, the HI of cows was higher in MixG during spring–summer and similar in both treatments during autumn–winter, implying that in MixG the effects on the cows HI of higher alfalfa proportion and herbage accumulation rate evolving from lower residual herbage mass in the previous cycle counteracted that of a higher HO in CowG. The HI of ewes was sufficient to enable satisfactory performance as breeding ewes. Thus, the benefits of mixed sequential grazing arose from higher herbage accumulation, positive changes in botanical composition, and the achievement of sheep production without negative effects on the herbage intake of cows.     

不同放牧强度对多年生黑麦草─白三叶草地叶片数量特征的影响

不同放牧强度在同一季节对黑麦草和白三叶的叶片数及单位面积总叶量的影响均不显著,单枝叶片数也不显著。随着季节的变化黑麦草叶量减少而白三叶则增加,但草地总叶量呈减少趋势。在7～8月两种草的叶面积指数在中、低放牧强度下显著(P<005)高于高放牧强度。黑麦草的单叶面积受季节影响较大。叶面积指数与生物量的回归分析表明,白三叶在中、低放牧强度下呈强正相关(P<001)。在高放牧强度下则呈显著相关(P<005)。草地总叶面积指数与生物量在中等放牧强度下呈强正相关(P<0.01),这与此时黑麦草的叶面积指数与其生物量间相关显著(P<005)有关。     

Growth patterns of Italian ryegrass cultivars established in different seasons

Abstract

A comparison is made between various Italian ryegrass cultivars established under irrigation on a well‐drained upland site during the traditional autumn months, with plantings of the same cultivars at other times of the year.

The dates on which pastures could be utilized for the first time, their relative growth patterns as well as weed infestation, flowering behaviour and persistency, were investigated. Some herbage quality determinations were also made.

February plantings are considered the most favourable for maximum late autumn, winter and spring production. First utilization following late autumn/winter plantings is, however, delayed considerably with the onset of cold weather. Late winter/early spring plantings, on the other hand, delay flowering for up to 16 months and the biennial growth pattern indicates vigorous growth immediately after planting, the possibility of variable late summer production followed by extremely poor autumn and winter production. This casts serious doubt on the merit of such a practice at the total exclusion of the traditional autumn plantings. Summer weed infestation from such spring plantings also gave cause for concern.