Pattern of herbage intake rate and bite dimensions of rotationally grazed dairy cows as sward height declines

To allow improved prediction of daily herbage intake of dairy cows in rotational grazing systems, intake behaviour was assessed throughout the day in 24‐h paddocks. Herbage intake in 16 lactating Holstein–Friesian cows was assessed using the short‐term (1‐h) weight gain method at four predetermined natural meal times throughout the day (early morning, T1; late morning, T2; mid‐afternoon, T3; and early evening, T4). The study comprised two 4‐day experiments, each with a cross‐over design of four blocks. In both experiments, cows grazed a 24‐h paddock daily, and the effect of the immediately previous grazing experience on intake behaviour was investigated throughout the day, taking account of daily fluctuations in the short‐term physiological condition of the cows. Experiment 1 was carried out to investigate overall grazing behaviour during meals as a sward is progressively depleted during the day, with intake being assessed within the paddock and, hence, on a depleted sward. Experiment 2 similarly investigated the effect of sward depletion and physiological condition throughout the day on intake, but cows were removed to fresh, undefoliated swards during intake measurement periods; thus, intake rate was not influenced by differences in sward condition. Intake behaviour from both experiments was compared to establish the effect on herbage intake of changes in sward state and non‐sward factors. In Experiment 1, sward surface height, available herbage mass, proportion of leaf and green leaf mass declined as the day progressed. Bite mass declined with sward depletion, and mean intake rate was 1·64 kg dry matter (DM) h^–1, which was significantly lower at T3 (P < 0·01) than during other meals. In Experiment 2, plot sward conditions did not change throughout the day, and intake behaviour also remained constant, with a mean intake rate of 2·11 kg DM h^–1. Mean bite depth as a proportion of pregrazing extended tiller height was constant throughout the day (mean 0·32). The results show that, although cows grazed throughout the day on progressively depleted swards, indicative of rotationally grazed paddocks (Experiment 1), bite mass declined linearly and intake behaviour was variable. However, where intake was assessed on high‐quality, undefoliated swards (Experiment 2), intake behaviour was similar regardless of the time of day and the immediately previous experience. There was some indication of an interaction between the effects of the sward and the physiological condition of the animal on herbage intake.     

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 herbage mass and allowance on sward characteristics,milk production,intake and rumen volatile fatty acid concentration

The objective of this study was to examine the effect of herbage mass and daily herbage allowance (DHA) on sward characteristics and animal performance, dry‐matter intake, rumen pH and volatile fatty acid production of unsupplemented spring‐calving dairy cows throughout the main grazing season. Sixty‐eight Holstein‐Friesian dairy cows were randomly assigned across four treatments (n = 17) in a 2 × 2 factorial design. Two swards were created with different levels of pre‐grazing herbage mass [allocated above 4 cm (>4 cm); 1700 kg DM ha^?1 (medium; M) or 2200 kg DM ha^?1 (high; H)] and two levels of DHA (>4 cm; 16 or 20 kg DM per cow d^?1). An additional eight lactating ruminally cannulated Holstein–Friesian dairy cows were randomly assigned to each treatment in a replicated 4 × 4 Latin square design. Sward and animal measurements were collected across four periods each of 1 week duration in April and May (PI) and July and August (PII). Maintaining the medium‐mass sward across the season improved the nutritive value of the sward in the latter part of the grazing season compared with high‐mass swards, thus resulting in increased animal intakes and milk production throughout PII. The higher organic matter digestibility of the medium‐compared with high‐masses during PII indicates that grazing severity and herbage mass in the spring to mid‐summer period will determine sward quality parameters in the late summer period.     

The effects of autumn closing date on sward leaf area index and herbage mass during the winter period

The provision of grass for early spring grazing in Ireland is critical for spring calving grass‐based milk production systems. This experiment investigated the effect of a range of autumn closing dates (CD), on herbage mass (kg DM ha^?1), leaf area index (LAI) and tiller density (m^?2) during winter and early spring. Thirty‐six grazing paddocks, closed from 23 September to 1 December 2007, were grouped to create five mean CD treatments – 29 September, 13 October, 27 October, 10 November, 24 November. Herbage mass, tiller density and LAI were measured every 3 weeks from 28 November 2007 to 20 February 2008; additionally, herbage mass was measured prior to initial spring grazing and tiller density was measured intermittently until September 2008. Delaying CD until November significantly (P < 0·05) reduced herbage mass (by approximately 500 kg DM ha^?1) and LAI (by approximately 0·86 units) in mid‐February. On average, 35% of herbage mass present on swards on 20 February was grown between 28 November and 30 January. LAI was positively correlated with herbage mass (R² = 0·78). Herbage mass increased by approximately 1000 kg DM ha^?1 as spring grazing was delayed from February to April. Tiller density increased from November to February, although it did fluctuate, and it was greatest in April (9930 m^?2). This experiment concludes that in the south of Ireland adequate herbage mass for grazing in early spring can be achieved by delaying closing to early mid‐October; swards required for grazing after mid‐March can be closed during November.     

The influence of weight of ryegrass per unit area and treatment at and after mowing on rate of drying

The rates of drying of perennial ryegrass, subjected to different treatments at mowing and after mowing, were assessed in the field by weight change of grass fresh weight in wire-mesh trays over 3·5 d (76 h). In a 5 × 3 × 3 factorial experimental design, the effects of five weights of grass per unit area [1·5, 3, 6, 12 and 24 kg fresh material (FM) m^?2], three treatments at mowing (no treatment, mower-conditioned, flail-treated) and three treatments after mowing (no treatment, inverted, mixed) were examined. The experiment was replicated twice on 16 occasions in 1992 at the Agricultural Research Institute of Northern Ireland. This gave a total of thirty-two replicates per treatment. The trays were weighed at 2-h intervals from 09.00 to 17.00 h each day. Data sets were restricted to rain-free days and also to the first day after mowing (day 1). On day 1, grass weight per unit area was a major factor dictating drying; reducing the grass weight per unit area of unconditioned grass from 6 to 3 kg FM m^?2 increased grass drying rate by 47%. There was no significant (P > 0·05) benefit over the untreated grass on day 1 from mixing or turning mower-conditioned or the unconditioned grass. Mixing of the flail-treated grass improved drying rate significantly (P > 0·001) over the control. Over the whole 76-h period, the relative benefit from either mower conditioning or flail treatment over no treatment was dependent upon both grass weight per unit area and initial dry-matter (DM) concentration. At higher initial DM concentrations (>150 g kg^?1) and lower grass weights (<6 kg FM m^?2) both mower conditioning using a nylon brush type conditioner and intensive conditioning by flail treatment gave substantial increases in drying over no treatment. Moisture regain of grass exposed to overnight dew was small. Rain had a much greater effect than dew on subsequent moisture regain. Unconditioned grass at 12 kg m^?2 retained 82% less water following rainfall than unconditioned grass at 3 kg m^?2.     

Effect of different grazing management systems on the herbage mass and pasture height of a Nardus stricta grassland in western Scotland, United Kingdom

The aims of this study were to examine the effect of three grazing treatments (year‐round stocking rates of 0·8 ewes ha^?1, 0·5 ewes ha^?1 and 0·5 ewes ha^?1 plus grazing cattle in summer), imposed for 4 years, on the herbage mass and surface height of a Nardus stricta‐dominated grassland in western Scotland and to obtain estimates of annual productivity of this grassland. Nardus stricta‐dominated grassland comprised proportionately 0·20 of the grazing area. Stocking rate of sheep had no significant effect on the herbage mass of the grassland in the first 2 years of the experiment, although mean summer pasture heights were significantly higher under the lower stocking rate of sheep. The pasture on the treatment with cattle grazing in summer had a significantly lower herbage mass and lower surface height than the two sheep‐only grazing treatments. Year‐to‐year variation in the herbage mass and surface height of herbage in summer was greater than the effect of treatments. Despite changes in surface height, the structural diversity of the grasslands was not increased by the treatments. The annual production of vascular plant material ranged from 417 g DM m^?2 in 1994 to 628 g DM m^?2 in 1996.     

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.     

The effects of rate and timing of application of fertilizer nitrogen in late summer on herbage mass and chemical composition of perennial ryegrass swards over the winter period in Northern Ireland

A small‐plot experiment was carried out in Northern Ireland on a predominantly perennial ryegrass sward over the period July 1993 to March 1994 to investigate the effect of timing and rate of fertilizer nitrogen (N) application on herbage mass and its chemical composition over the winter period. Eighty treatment combinations, involving four N fertilizer application dates (28 July, 9 and 30 August and 20 September 1993), four rates of N fertilizer (0, 30, 60 and 90 kg N ha^?1) and five harvest dates (1 October, 1 November, 1 December 1993, 1 February and 1 March 1994), were replicated three times in a randomized block design experiment. N application increased herbage mass at each of the harvest dates, but in general there was a decrease in response to N with increasing rate of N and delay in time of application. Mean responses to N applications were 13·0, 11·5 and 9·5 kg DM kg^?1 N at 30, 60 and 90 kg N ha^?1 respectively. Delaying N application, which also reduced the length of the period of growth, reduced the mean response to N fertilizer from 14·3 to 7·4 kg DM kg^?1 N for N applied on 28 July and 20 September respectively. Increasing rate of N application increased the N concentration and reduced the dry‐matter (DM) content and water‐soluble carbohydrate (WSC) concentration of the herbage but had little effect on the acid‐detergent fibre (ADF) concentration. Delaying N application increased N concentration and reduced DM content of the herbage. The effect of date of N application on WSC concentration varied between harvests. A decrease in herbage mass occurred from November onwards which was associated with a decrease in the proportion of live leaf and stem material and an increase in the proportion of dead material in the sward. It is concluded that there is considerable potential to increase the herbage mass available for autumn/early winter grazing by applying up to 60 kg N ha^?1 in early September.     

A method for approximate on‐farm estimation of herbage mass by using two assessments per pasture

Appropriate pasture management requires implementation of methods that reduce the time and labour required for assessing herbage mass. In this study, Monte Carlo simulations and a field study were used to evaluate a simple method for estimating herbage mass based on the corrected average of the single highest and lowest mass values in a pasture. The necessary correction factor for the method was objectively derived using a single nonlinear equation based on the scaled difference between the highest and lowest herbage mass regardless of the mean and variance of mass and pasture size. The accuracy of estimation using this method is acceptable for on‐farm use: more than 90% of the estimates had error rates below 20% of the true value when the plot size assessed was larger than 64 m² in the simulation study; in the field experiment, approximately half of the estimates had error rates below 20% of the observed mean of random samples (R² = 0·71). The advantages of the proposed method are that it requires only two assessments per pasture and that selection of assessment plots is straightforward. This method has potential for obtaining approximate on‐farm estimates of herbage mass that could help improve pasture management.     

Effects of application of nitrogen fertilizer on concentrations of P, K, S, Ca, Mg, Na, Cl, Mn, Fe, Cu and Zn in perennial ryegrass/white clover pastures in south-western Victoria, Australia

Effects of timing and rate of N fertilizer application on concentrations of P, K, S, Ca, Mg, Na, Cl, Mn, Fe, Cu and Zn in herbage from perennial ryegrass/white clover pastures were studied at two sites in south-western Victoria, Australia. Nitrogen fertilizer (0, 15, 25, 30, 45 and 60 kg ha^–1) was applied as urea in mid-April, early May, mid-May, early June and mid-June 1996 to pastures grazed by dairy cows. At Site 1, N fertilizer resulted in a linear increase in P, K, S, Mg and Cl concentrations in herbage and a linear decrease in Ca concentration. For all times of application, concentrations of P, K, Ca, Mg and Cl in herbage increased by 0·0048, 0·08, −0·010, 0·0013 and 0·053 g kg^–1 dry matter (DM) per kg N applied respectively. For S concentration, maximum responses occurred in mid-May (0·012 g kg^–1 DM per kg N applied). At Site 2, N fertilizer resulted in a linear increase in P, S and Na concentrations in herbage, a linear decrease in Ca concentration and a curvilinear increase in K and Cl concentration. The maximum responses for P, S and K concentrations in herbage occurred for the N application in mid-June and were 0·015, 0·008 and 0·47 g kg^–1 DM per kg N applied respectively. For Cl concentration, the maximum response occurred for the N application in early June and was 0·225 g kg^–1 DM per kg N applied. Overall, applications of N fertilizer up to 60 kg ha^–1 did not alter herbage mineral concentration to levels that might affect pasture growth or animal health.     

The effects of defoliating grass in winter or spring on herbage yields and ensilage characteristics

Under Irish conditions, the digestibility in May of grass managed for silage production is sometimes lower than expected. In each of two successive years, replicate field plots were established to examine the effects of three defoliation heights (uncut or cut to a stubble height of 10 or 5 cm) applied in winter and/or spring on herbage yields harvested in May and again in July, and on chemical composition and conservation characteristics associated with first‐cut silage. Swards that were not defoliated in December or March had a dry‐matter (DM) yield and in vitro DM digestibility (DMD) in mid‐May of 6597 kg ha^?1 and 736 g kg^?1, respectively, in Year 1, and corresponding values of 7338 kg ha^?1 and 771 g kg^?1 in Year 2. Defoliating swards to 5 cm in December reduced (P < 0·001) May DM yields compared to swards that were not defoliated in both December and March, while herbage DMD in May increased (P < 0·001) when defoliated in December or March. There were no clear effects of defoliation height or its timing on herbage ensilability or resultant conservation efficiency characteristics. The effects of defoliation on July yield were the reverse of those observed for May, while the total yield of the December and March defoliations plus the two silage harvests increased as defoliation height was lowered in Year 2 only. It is concluded that defoliation in winter and/or spring can increase herbage digestibility but will likely reduce DM yields in May.     

Effect of nitrogenous fertilizer on production per animal and per unit area by beef cattle offered similar daily allowances of herbage

An experiment repeated in 3 consecutive years in which 0, 200, 400 and 600 kg ha^?1 fertilizer N was applied annually is described. Cattle on all treatments were offered the same constant daily amount of 2.0 kg herbage DM per 100 kg liveweight above a 3.4 cm height of defoliation. Digestible OM intakes and daily rates of gain were in general not significantly different between treatments. Area required to support these intakes and gains however differed significantly between treatments (P < 0.001) and resulted in high outputs of liveweight gain per hectare on all treatments when compared with other published studies. These outputs together with other actual and theoretical outputs were used to predict optimum fertilizer N applications for grazing beef cattle and the predictions discussed in relation to commercial practice.     

Seasonal changes in herbage mass and nutritive value of a range of grazed legume swards under Mediterranean and cool temperate conditions

Seasonal changes in herbage mass and herbage quality of legume‐based swards under grazing by sheep or cattle were investigated at four locations in climatically different zones of Europe: Sardinia (Italy), southern France, northern Germany and south‐west England (UK). At each location standard treatments were applied to legumes typical of species widely used in each locality: Medicago polymorpha in Italy, Medicago sativa in France, and Trifolium repens in Germany and in UK. At each site comparisons were made of two other legumes: Trifolium subterraneum and Hedysarum coronarium in Italy, Onobrychis sativa and Trifolium incarnatum in France, Trifolium pratense and Lotus corniculatus in Germany, and Trifolium ambiguum and L. corniculatus in UK. Legumes were sown in mixture with locally appropriate companion grasses, and measurements were made over two or three grazing periods. In Italy M. polymorpha swards gave the greatest herbage mass in grazing period 1 but H. coronarium was more persistent. At the French site all legumes established poorly with no significant herbage mass differences between treatments. At both the UK and German sites L. corniculatus maintained a high proportion of legume in the sward; T. repens showed poor persistence under continuous sheep grazing in UK but persisted under cattle grazing in Germany, while T. ambiguum was slow to establish in the UK, and T. pratense proved to be of comparable herbage mass to the standard T. repens‐based sward in the last year of the experiment. The concentration of crude protein and in vitro digestibility of organic matter in the dry matter of herbage showed greater within‐season variation than between treatments at each site. It is concluded that, in addition to currently used species, legume‐based swards containing H. coronarium, O. sativa and L. corniculatus all have potential to contribute to forage production for low‐input grazing and their use merits further consideration in systems of livestock production in Europe.     

中国油菜单产增长要素贡献率分析

运用因子分析技术将影响中国油菜单产的众多因素综合为物质费用、劳动力、政策制度和“结构与灾害”四大因素,并利用Cobb-Douglas型生产函数模型分别测算了四大因素在中国油菜单产增长中的贡献率。根据1990-2004年间的数据计算,物质费用对中国油菜单产增长的贡献率最大,其次是劳动力和政策制度,而同期“结构与灾害”因子对单产有负向影响。     

Effects of species aggregation, habitat and season on the accuracy of double-sampling to measure herbage mass in a lowland grassland ecosystem

Double‐sampling, as a cost‐effective and sufficiently accurate method, is an acknowledged method for estimating herbage mass at the level of the plant species up to the total plant community. It was investigated whether adjusting visual estimations of double‐sampling is applicable at different levels of species aggregation when different seasons and habitats are involved. The method was used in six different habitats of the same ecosystem, a grassland nature reserve in western Belgium, based on eight sampling periods. A general linear model was used to analyse the data at four levels of species aggregation. The correlation between estimated and measured values of herbage mass was significant for the majority of graminoid species at the levels of the sub‐life‐form and total plant community but not at the level of the life‐form. Interaction of habitat type and measured herbage mass, and interaction of date and measured herbage mass, were significant for a minority of species. A significant interaction of both date and habitat with measured herbage mass was found in some cases at the level of the sub‐life‐form and total plant community. Results suggest that the double‐sampling method is reliable for most graminoids and at the sub‐life‐form level, but should be applied more cautiously for forbs species, and when different sampling periods and habitat types are involved at the level of the life‐form. To avoid producing several calibration lines at the level of the species and to overcome deficiency of observations at this level, lumping morphologically similar species from the same vegetation stratum in sub‐life‐form groups is recommended for adjusting estimated herbage mass.     

Effects of continuous or rotational grazing of two perennial ryegrass varieties on the chemical composition of the herbage and the performance of finishing lambs

Plant breeding has developed perennial ryegrass varieties with increased concentrations of water‐soluble carbohydrates (WSCs) compared with conventional varieties. Water‐soluble carbohydrates are major metabolic and storage components in ryegrass. Therefore, if perennial ryegrass herbage is allowed to grow to greater heights it should contain higher water‐soluble carbohydrates concentrations, for example as under rotational grazing rather than continuous grazing by livestock. This study investigated this hypothesis and measured the performance of lambs grazed rotationally and continuously. Replicated plots of the variety AberDart (bred to express high WSC concentrations) or the variety Fennema were grazed by a core group of ten male Cheviot lambs for 10 weeks. Lambs were weighed and replicate forage samples were taken every 7 d. Concentrations of WSC in AberDart herbage were significantly (P < 0·05), but not substantially, higher than those in Fennema herbage. Rotational grazing did not increase the differential in WSC concentration between the AberDart and Fennema varieties. However, there was a tendency (P = 0·07) for lambs rotationally grazing the AberDart swards to have a higher final live weight than lambs grazing the Fennema swards. Overall, lamb performance was increased when either perennial ryegrass variety was rotationally rather than continuously grazed (P < 0·001).     

Effect of temperature regime on germination of seed of perennial ryegrass (Lolium perenne)

Perennial ryegrass ( Lolium perenne L.) is one of the most valuable temperate pasture grasses in the world. Understanding seed germination in response to temperature can help determine its optimal seeding times. Germination tests for two cultivars of perennial ryegrass (cv. 'Turfstar' and cv. 'Transtar') were conducted by applying thirty-six constant and alternating temperature regimes, ranging from 5 to 40°C (16 h night/8 h day). Responses in germination rate to these temperature regimes were then used to construct a quadratic response surface, giving estimated germination rates with confidence intervals at P  ≤   0·05 for both cultivars. Optimum germination rate occurred over a range of regimes: 15/25, 20/25, 20/30 and 25/30°C. Furthermore, a wide range in diurnal alternating temperatures resulted in maximum seed germination rate for cv. 'Transtar', while no constant temperature regime supported maximum germination rate for cv. 'Turfstar'. A temperature-dependent germination rate function for perennial ryegrass was developed which could be used in the future to predict location-specific optimum seeding times when national or regional monthly temperature data are available.     

Spring and autumn animal treading effects on pre‐grazing herbage mass and tiller density on two contrasting pasture types in Ireland

A perennial ryegrass (Lolium perenne L.)‐dominated sward on a well‐drained soil (Experiment 1) and a creeping bent (Agrostis stolonifera L.)‐dominated sward on a poorly drained soil (Experiment 2) were subjected to four treading treatments: control (C, no damage), light damage (L), moderate damage (M) or severe damage (S) to quantify the effects on herbage dry‐matter (DM) production and tiller density. In Experiment 1, treading damage was imposed in spring. In Experiment 2, one‐third of the site was damaged in autumn, one‐third in spring and one‐third in both spring and autumn. Both sites were rotationally grazed after treading treatments. Pre‐grazing herbage mass was measured eight times in Experiment 1 and seven times in Experiment 2 on each plot, and tiller density was assessed four times in each experiment. In Experiment 1, pre‐grazing herbage mass was reduced by 30% in S plots at the first harvest after damage, but cumulative pre‐grazing herbage DM production was not different between treatments (12·7 t DM ha^?1). In Experiment 2, annual cumulative pre‐grazing herbage mass was reduced by between 14 and 49%, depending on intensity of treading damage event and season when damage occurred. Tiller density was not affected by treatment in either experiment. A perennial ryegrass‐dominated sward on a well‐drained soil was resilient to heavy treading damage. A creeping bent‐dominated sward on poorly drained soil requires a more careful grazing management approach to avoid major losses in cumulative pre‐grazing herbage mass production during wet weather grazing events.     

Effects of ruminal fill on short-term herbage intake rate and grazing dynamics of beef heifers

The impact of manipulating ruminal fill (RF) on intake rate of herbage and grazing dynamics was measured with three rumen‐cannulated beef heifers grazing Bermudagrass pastures individually. The treatments compared were removal of proportions of rumen contents of 0 (treatment RF0), 0·33 (treatment RF33), 0·66 (treatment RF66) and 1·00 (treatment RF100). Treatments were randomly applied in a 3 × 4 Youden‐square design. The rumens were emptied before and after planned grazing sessions (30 min) to set up the treatments, and to estimate intake rate and bite mass, respectively. Measurements were made of bite rate, bites per feeding station, feeding stations per minute, intake per feeding station, time per feeding station, eating and searching step rates and times. Apparent bite area and area grazed per feeding station were calculated. Ruminal fill affected short‐term intake rate and changed grazing dynamics. As RF increased, step rates, searching times, bite mass, apparent bite area, bites per feeding station, area grazed per feeding station, time per feeding station and intake per feeding station decreased (P < 0·01) while step times, eating step rates and bite depth increased (P < 0·01). The results of the present study indicate that RF is an important factor governing the intake characteristics and behaviour of grazing beef heifers.     

Evaluation of the effects of ewe prolificacy potential and stocking rate on herbage production,utilization, quality and sward morphology in a temperate grazing system

This study investigated the effect of ewe prolificacy potential (PP; predicted number of lambs born ewe^?1 year^?1), stocking rate (SR; ewes/ha) and their interaction on herbage dry matter (DM) production, utilization, quality and sward morphology within a temperate grass‐based lamb production system. The study had a 2 × 3 factorial design, consisting of two ewe PP as dictated by sire breed (180 medium prolificacy potential (MP—Suffolk crossbred) and 180 high prolificacy potential ewes (HP—Belclare crossbred)) and three SR: low (LSR; 10 ewes/ha), medium (MSR; 12 ewes/ha) and high (HSR: 14 ewes/ha). Each treatment was managed in a rotational grazing system, with LSR, MSR and HSR treatments grazing to target post‐grazing sward heights (PGSH) of 4.55, 4.15 and 3.75 cm respectively. Herbage DM production (above target PGSH) and utilization were highest at the HSR, intermediate at the MSR and lowest at the LSR (p < .001). Ewe PP had no effect on herbage DM production, utilization, quality or sward morphology (p > .05). The proportion of leaf in the sward (above target PGSH) was 4% greater in MSR and HSR compared with LSR (p < .05). In conclusion, findings demonstrate the potential to support increased ewe PP through the selection of ewe genotypes of a genetically higher PP and lower mature live weight and increased SR within a temperate grass‐based lamb production system.