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.     

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.     

Grazing methods and stocking rates for direct-seeded alfalfa pastures: I. Plant productivity and animal performance

A 4-yr study was conducted to determine the effects of two grazing methods (GM) at two stocking rates (SR) on alfalfa pasture plant productivity and animal performance and to ascertain the effect of grazing systems on subsequent performance of steers fed a high-concentrate diet. Eight pasture plots (.76 ha) were seeded in 1988 with alfalfa (Medicago sativa L. var. WL225) and divided into two blocks of four pastures each. Grazing methods consisted of a traditional four-paddock or an intensive 13-paddock system. Pastures were managed to allow a 36-d rest period with an average grazing season of 110 d. The low and high SR were 5.9 vs 11.7, 5.3 vs 10.5, 5.3 vs 7.9, and 5.3 vs 7.9 steers/ha for years 1989 to 1992, respectively. Following the grazing season, steers were placed in a feedlot and fed a high-concentrate diet (81% high-moisture corn, 14% corn silage, 5% protein-mineral supplement) for an average of 211 d. There was no effect of GM on herbage mass, pasture phase ADG, or live weight gain/hectare. Increasing the number of paddocks was beneficial when herbage mass was limited and stocking rate was above 7.9 steers/ha. Increasing SR above 7.9 steers/ha decreased herbage mass and pasture-phase ADG. As forage allowance increased, pasture-phase ADG increased quadratically (R2 = .82, P < .001), reached a plateau, and then decreased. Previous grazing system did not influence the performance of steers in the feedlot or their carcass characteristics. Optimum SR is dependent on herbage mass produced.     

The effect of veld condition on the quality of diet selected by cattle grazing the Natal Sour Sandveld

The quality of diet selected by steers fistulated at the oesophagous was related to veld condition in a simulated rotational grazing system on the Natal Sour Sandveld. Six camps, ranging in veld condition score from 8,5 to 53%, were grazed simultaneously for a two‐week period in spring, summer, autumn and winter. Fistula samples were collected on the first, middle and last day of a period of occupation in a camp. Samples were analysed in terms of crude protein (CP), in vitro digestibility (IVD) and plant‐part (% leaf, % stem and % dead material) composition. Dietary quality in terms of CP, IVD and plant‐part composition was not related to veld condition but was dependent largely (P≤0,01) upon season and to a lesser extent upon period of occupation in a camp. It was concluded that in sourveld areas, where dietary quality may be limiting, the veld condition score may be a poor index of potential animal production.     

Pasture management effects on diet composition and cattle performance on continuously stocked rhizoma peanut-mixed grass swards

In Florida, rhizoma peanut (RP; Arachis glabrata Benth.), a tropical legume, combines the attributes of excellent nutritive value, competitive ability with tropical grasses, and high animal performance. The objective of this study was to determine the effects of spring N fertilization (0 vs 35 kg/ha) and summer stocking rate (1.5 and 2.5 bulls/ha) on herbage mass, nutritive value, herbage allowance, and diet botanical composition of grazed RP-grass swards and their interaction with growth and development of bulls (Senepol, and Brahman or Angus). The study was conducted in 1995 and 1996 at the USDA, ARS, Subtropical Agriculture Research Station in Brooksville, FL. Nitrogen was applied in April of each year, and all pastures were stocked with 1.5 bulls/ha until approximately July of each year, when stocking rate was increased on half the pastures to 2.5 bulls/ha. Herbage mass (HM, kg/ha), herbage allowance (HA, kg/kg BW), nutritive value (CP and in vitro organic matter digestibility [IVOMD]), and diet botanical composition (fecal microhistological) readings were determined. Animal measurements included total and seasonal (spring vs summer), ADG, hip height (cm), scrotal circumference (SC, cm), and plasma urea nitrogen (PUN, mg/dL). Herbage mass (3.0 +/- 0.12 Mg/ha and 3.4 +/- 0.13 Mg/ha in 1995 and 1996, respectively) was not affected by nitrogen fertilization or stocking rate but was affected by season (P < 0.05) due to increased plant growth rate associated with summer rainfall. Stocking rate did affect herbage availability, but it never fell below 3 kg/kg BW, indicating herbage availability was never limiting. Crude protein (200 to 140 g/kg) and IVOMD (650 to 540 g/kg) were not affected by treatment, but declined (P < 0.001) from spring until fall. Treatments also had no effect on diet botanical composition. Summer ADG averaged about 0.2 kg/d lower than spring ADG, due, in part, to seasonal declines in nutritive value. Because herbage allowance was never limiting, full-season ADG was not affected by stocking rate or N fertilization and averaged 0.61 +/- 0.03 and 0.60 +/- 0.02 kg/d in 1995 and 1996, respectively. There were season x breed interactions (P < 0.05) for ADG due to greater declines during the summer for Angus than for Senepol or Brahman. There were no differences in final BW, SC, BCS, hip height, or PUN due to treatments, but breed differences were noted (P < 0.05) for all measures except BCS.     

Effects of establishment method and fall stocking rate of wheat pasture on forage mass, forage chemical composition, and performance of growing steers

Stocking rate is a fundamental variable for managing pastures, and there is a distinct relationship between stocking rate and animal performance for each forage type. This research was conducted to determine the effects of fall stocking rate (SR) and method of establishment of wheat pasture planted into dedicated crop fields on animal performance during the fall and subsequent spring. There was a factorial arrangement of tillage methods used in the establishment of wheat pasture and fall stocking rates. Tillage treatments included 1) CT, seed sown into a prepared seedbed, 2) RT, a single pass with a light disk followed by broadcasting of seed, or 3) NT, direct seeding into the undisturbed stubble of the grazed-out wheat pasture from the previous year. The fixed SR during the fall were 1.9, 2.5, and 3.7 growing beef steers (Bos taurus L.)/ha. In the spring all pastures were grazed at the same fixed SR by steers for graze out. Data were analyzed using the mixed procedure of SAS as a randomized complete block design with field as the experimental unit and year as the block. Forage mass, forage nutritive composition, and animal performance during the fall or spring were not affected (P ≥ 0.14) by tillage method. During the fall grazing season, with increasing SR there were linear (P < 0.01) decreases in BW of steers upon removal from pasture, BW gain per steer, and ADG, whereas grazing-day per hectare and BW gain per hectare increased linearly (P < 0.01) with increasing SR. The carryover effects of fall SR into the spring grazing season decreased (P< 0.01) grazing-day per hectare and tended (P ≤ 0.09) to produce quadratic changes in BW upon removal from pasture and BW gain per hectare. Across the fall and spring grazing seasons, grazing-day per hectare increased linearly (P < 0.01) with greater SR, and BW gain per hectare increased quadratically (P = 0.02) with increased fall SR. A tillage treatment by fall SR interaction (P = 0.10) indicates that although there was no difference (P ≥ 0.12) due to tillage treatment in BW gain per hectare at 1.9 or 2.5 SR, NT fields produced (P ≤ 0.04) more BW gain per hectare than CT or RT at the 3.7 SR. Although increasing SR of growing steers leads to reduced animal performance in the fall and reduced carrying capacity in the spring, NT appears to be capable of withstanding greater fall SR with less impact on total production per hectare than CT or RT.     

Sward characteristics, grass dry matter intake and milk production performance is affected by timing of spring grazing and subsequent stocking rate

The objective of this study is to investigate the effect of contrasting spring grazing dates (GD) and stocking rate (SR) on sward characteristics, grass dry matter intake and milk production performance of autumn calving dairy cows during the spring period. Two swards were created by grazing in March (early grazing; E) or by delaying first grazing until mid-April (late grazing; L). Two stocking rates, high (H; 5.5) and medium (M; 4.5) were applied across each sward. Forty eight autumn calving Holstein cows (160 ± 35 days in milk) were assigned to one of four (n = 12) different grazing treatments. The experiment began on April 17th and finished after 2 grazing rotations on June 20th. Later spring grazing significantly increased herbage mass (kg DM/ha) above ground level (+ 933, P < 0.05) and > 50 mm (+ 738, P < 0.05). Compressed sward height (+ 22.1 mm, P < 0.05), extended tiller height (+ 73 mm, P < 0.001) and pseudostem height (+ 35 mm, P < 0.001) were also significantly higher for later grazed swards. In the grazing horizon (> 80 mm— extended tiller height), later grazed swards had significantly lower leaf proportion (− 0.09, P < 0.05) and higher dead material (+ 0.05, P < 0.001). Daily herbage allowance (> 50 mm) was on average 12.7, 15.9, 18.2 and 21.9 kg DM/cow for EH, EM, LH and LM, respectively. Daily leaf allowance (> 80 mm) was 10.1, 12.3, 13.3 and 14.5 kg DM/cow for EH, EM, LH and LM, respectively. The EM (16.2 kg DM/cow), LH (+ 0.1 kg) and LM (0.8 kg) treatments all had similar grass DM intake, however there was evidence of an interaction (P < 0.10) between GD and SR, this was due to the low grass DM intake of the EH (13.9 kg DM/cow) treatment. When expressed as UFL (Fill unit) intake the EM treatment recorded the highest value. There was a significant interaction between GD and SR (P < 0.01) for milk, protein yield, 4% fat corrected milk yield (P < 0.05) and protein concentration (P < 0.001). Cows grazing the EM treatment produced 23.9 kg of milk, 876 and 685 g of fat and protein yield. The difference in milk production (cow/day) between EM and EH treatments was + 3.6 kg milk, + 98 g fat and + 107 g protein. The production yield difference between LM and LH treatments was + 1.1 kg milk, + 27 g fat and + 29 g protein in favour of the LM treatment (23.9 kg of milk, 877 and 687 g fat and protein yield). Herbage quality and morphological characteristics are clearly improved with early spring grazing as herbage mass is reduced on subsequent rotations. Swards grazed in early spring allow higher grass utilisation and high milk production performance when grazed at a medium stocking rate. Improved milk production from herbage can be achieved provided herbage mass and allowance are maintained at levels where herbage quality decreases are minimised.     

Technical note: stocking equivalents and stocking rate-gain relationships for steers and cow-calf pairs grazing oversown bermuda grass.

Grazing experiments may use steers or cow-calf pairs for measuring animal performance on pasture treatments, but the validity of extrapolation between these classes of cattle has not been verified. A grazing study was conducted in the spring and summer of both 1988 and 1989 to determine stocking equivalents and stocking rate-weight gain relationships for steers and cow-calf pairs grazing Coastal bermuda grass (Cynodon dactylon [L.] pers.) oversown with rye (Secale cereale L.) and ryegrass (Lolium multiflorum Lam.). Average daily gain and stocking rate (SR; 3.2, 4.2, 6.2, and 7.4 animals per hectare for steers and 1.7, 2.5, 3.7, and 4.9 pairs per hectare for cow-calf pairs) were both adjusted so that comparisons could be made on an equal BW basis. Disk meter height readings were used as measurements of forage accessibility. Disk meter height responses to SR did not differ (P greater than .10) between steer and cow-calf paddocks. There was a linear (P less than .001) decrease in ADG as SR increased, but this decline was steeper (P less than .001) for steers than for cows or suckling calves. Steers tended to be more productive than calves at low SR but less productive at high SR. Disk meter heights for the range of SR used in the study did not differ (P greater than .10) for steers and cow-calf pairs at equivalent BW per hectare. Our study suggests that live BW is a reasonable basis for determining forage requirements of steers and cow-calf pairs under grazing conditions, but extrapolation of production between classes of livestock will not be reliable.     

A study of animal production under different grazing regimes in the False Upper Karoo at Grootfontein

Three systems of animal production on the fragile Karoo veld, i.e. multi-paddock rotational grazing, pauci-paddock rotational grazing and continuous grazing were studied. Of these systems, multi-paddock rotational grazing gave the best results with continuous stocking resulting in the worst. All three systems studied had long histories of both continuous stocking- and of pauci-paddock rotational grazing. The veld, under both these previous systems of management has stabilised, but at different seral stages. The continuously stocked range stabilised in the early developmental seral stage, consisting mainly of annual grasses. The veld under pauci-paddock rotational management stabilised in the early to mid-developmental seral stage, consisting mainly of perennial grasses. Experimentation on veld in a stable condition is a prerequisite if valid conclusions in respect of rotational grazing and continuous stocking are to be drawn. Rotational grazing on overgrazed veld will result in poor animal performance, while it is generally accepted that continuous stocking on pristine veld will result in excellent animal performance for a number of years. Multi-paddock rotational grazing outperformed both pauci-paddock rotational grazing as well as continuous stocking on both types of veld. This is surprising taking into account the mid-seral stage condition of the vegetation. This supports the argument that with improved veld management, an improved production potential is possible on veld even in a degraded or current condition.     

Influence of stocking rate and grazing system on plant basal cover and botanical composition of veld in the northern cape 1

Abstract

Changes in basal cover and botanical composition were recorded at four stocking rates, both under continuous and rotational grazing in the Northern Cape. The experiment was conducted with cattle. Results suggested that heavier stocking rates could be applied under rotational grazing than under continuous grazing without veld deterioration occuring. After four seasons, botanical composition deteriorated only under continuous grazing. Plant basal cover decreased significantly at the heavy stocking rates, both under rotational and continuous grazing. This result illustrates the danger of grazing strategies based on an injudicious increase in stock numbers.

Basal cover was found to be a better indicator of trends in veld condition than botanical composition, despite annual fluctuations resulting from rainfall variability. Changes in the botanical composition apparently occur only where veld deterioration is more advanced.     

Impact of grazing intensity on herbage intake, composition, and digestibility and on live weight gain of sheep on the Inner Mongolian steppe

High grazing pressure during the last decades caused severe ecological problems in the steppe of Inner Mongolia, China. The objective of the present study was to determine the effects of grazing intensity of sheep on herbage mass (HM) and intake, chemical composition and digestibility of herbage, and on live weight gain (LWG). A grazing experiment with six different grazing intensities (1.5, 3.0, 4.5, 6.0, 7.5, and 9.0 sheep/ha) was conducted in the growing season of 2005 in the Xilin River Basin. HM decreased from 1.5 t DM/ha at the lowest grazing intensity to 0.6 t DM/ha at the highest grazing intensity. NDF content of the herbage was high (> 700 g/kg DM) and relatively constant, whereas acid detergent lignin (ADL) content increased with grazing intensity and with proceeding grazing season. Digestibility of organic matter ingested (DOM) tended to decrease with grazing intensity as well as intake of organic matter (OMI) and of digestible organic matter (DOMI) per sheep (P = 0.090 and P = 0.065, respectively), whereas LWG per sheep decreased with increasing grazing intensity (P = 0.018). DOM and OMI were negatively related to ADL content. However, herbage intake and LWG per ha increased with grazing intensity (P < 0.001) and reached their maximum at 9 and 7.5 sheep per ha, respectively. This observation confirms the current farmers' practise of high grazing pressure ignoring long term grassland productivity and ecological problems. Therefore, the studies are continued to provide further information on long term effects. This study could show pronounced effects of grazing intensity on animal and grassland productivity and the suitability of the methods applied to measure intake and digestibility of herbage in a large scale grazing experiment with sheep.     

Towards the development of a bioeconomic stocking model for the semi‐arid savanna of KwaZulu‐Natal

Abstract

Rainfall variability is a major determinant of system dynamics and profitability of livestock enterprises in arid and semi‐arid environments. Range managers consequently require detailed information on the financial and ecological implications of various stocking strategies in order to formulate viable management systems. Data collected over seven seasons (1986–1993), from a series of extensive grazing trials in the semi‐arid savanna of KwaZulu‐Natal with cattle stocked at three rates (0.17, 0.23 and 0.30 LSU ha^?1) were used to develop a bioeconomic stocking model (LOWBEEF). The model comprised two biological sub‐models (BEEF and GRASS), and an integrated economic component. The BEEF sub‐model related seasonal live mass gain to stocking rate and rainfall. The GRASS sub‐model related residual herbage at the end of summer to summer stocking intensity, range condition (indexed as the sum of proportions of three key forage species, Themeda triandra, Panicum maximum and P. coloratum) and rainfall. The period over which supplementary feeding would be required to maintain cattle mass was related to residual summer herbage mass. The biological sub‐models were linked to an economic component model (ECON) to reflect the influence of various environmental and economic parameters on profitability.     

Influence of stocking rate and grazing systems on available grazing in the northern cape 1

Abstract

The influence of rotational and continuous grazing systems, each applied with four stocking rates, on the above‐ground phytomass of veld was determined over four years.

Grazing systems showed a significant influence on available herbage during one year only. Increased stocking rates brought a progressive decline in above‐ground phytomass. During the fourth season (1980/81) the average grazing pressures at stocking rates of 10 ha, 7 ha, 5,5 ha and 4 ha/Large stock unit were 5 984 kg, 3 417 kg, 2 390 kg and 1 238 kg and 1 238 kg phytomass/Large stock unit, respectively. At the end of the fourth season (July, 1981) there was reserve grazing available on the various stocking rates for approximately 579 days, 337 days, 202 days and 76 days, respectively. The risk of high stocking rates in the marginal rainfall regions, is emphasised.     

The influence of stocking rate and grazing system on the crude protein content and digestibility of Tarchonanthus veld in the northern cape 1

Abstract

Four stocking rates (10, 7, 6 and 4 ha/large stock unit), in both rotational and continuous grazing, have been applied with cattle on Tarchonanthus veld. The crude protein content and digestibility of organic matter of handcut samples and herbage samples collected by means of oesophageal fistulated steers in the different treatments, were determined.

The results indicated that the crude protein content (3,9 to 6,7%) and digestibility (48,7 to 59,4%) of handcut samples was not representative of the diet of grazing cattle. The crude protein content of the samples collected by means of oesophageal fistulated steers varied from an average of 13,6%. (October to December) to an average of 5,3% (July and August). On average, the digestibility of the fistula collected samples varied between 60,4% (February to April) and 50,2% (July to October). The crude protein content of the fistula collected samples tended to increase with increasing stocking rate while digestibility declined. Both crude protein content and digestibility of the fistula collected samples did not differ significantly between rotational and continuous grazing.     

Forage production of some grass species in the false Thornveld of the Eastern Cape

Abstract

The most commonly occurring grass species in the False Thornveld (Acocks, 1953; veld type no. 21) were clipped before and after grazing on veld in good and poor condition at different times of the year. Herbage yield per species was expressed per unit basal tuft area, and the difference in yield before and after grazing was considered to reflect the production of available forage. Themeda triandra produced more forage than any other species at all times of the year. Sporobolus fimbriatus generally produced the second highest amount of available forage. Cymbopogon plurinodis, despite having the second highest herbage yield before grazing, was not grazed to a significant extent. On the basis of the results, Themeda triandra and Sporobolus fimbriatus were identified as key grass species in the False Thornveld of the Eastern Cape.     

Timing of herbage allocation in strip grazing: Effects on grazing pattern and performance of beef heifers

The timing of grazing bouts (GB) determines how cattle allot time to meet their nutritional needs. Net photosynthesis and evapotranspirational losses increase herbage nonstructural carbohydrate and DM concentrations, which may lead to longer and more intense GB at dusk. Hence, linking the grazing pattern, plant phenology, and herbage allocation time emerges as an option to manipulate the GB and nutrient intake. The objectives of this work were to analyze grazing behavior and performance of beef heifers when herbage allocation was at 0700 each morning (MHA) or at 1500 each afternoon (AHA). Two pairs of experiments were conducted during the winter and spring examining behavior and performance. Measurements were grazing, rumination, and idling times during daylight hours, and their patterns, as well as bite rate, ADG, change in BCS, and daily herbage DMI. In the behavioral experiments, 8 heifers strip-grazed annual ryegrass (Lolium multiflorum Lam.). The grazing, rumination, and idling times as well as bite rate were measured and also analyzed per time of day. In the performance experiments, 48 beef heifers strip-grazed annual ryegrass in 2 groups according to treatments. Daily DMI, ADG, and changes in BCS were analyzed. The AHA increased daily idling time (P < 0.01) and decreased grazing time (P < 0.01). The AHA concentrated grazing time in the evening, when bite rate was greater (P < 0.01). The daylight rumination time varied by time of day (P < 0.01), but total daylight rumination time did not differ (P = 0.11). With AHA, rumination time and idling time were concentrated in the morning and afternoon. In the performance experiment during the winter, there was a treatment x week effect (P < 0.01) for ADG and change in BCS. Beginning in wk 4, heifers in AHA gained 150 g of BW and 0.0145 points of BCS more than those in MHA (P < 0.05) per day. In the spring, AHA increased ADG by 549 g and 0.0145 points of BCS more than those in MHA (P < 0.05) per day during the entire 6 wk. The herbage DMI (kg/d) did not differ in winter (AHA, 5.0 vs. MHA, 4.5) or spring (AHA, 5.6 vs. MHA, 5.0). These results suggest that timing of herbage allocation alters grazing, rumination, and idling patterns; AHA leads to longer and more intense GB when herbage has greater quality, which improves cattle performance.     

Evaluation of veld potential in east griqualand using beef cattle under two grazing management systems

Abstract

Beef production from veld, in the short term, was found to be greater under a continuous grazing system than under a rotational grazing system. Average daily gains decreased from a maximum in late‐spring and the highest three‐year mean value was 0,5 kg/animal/day. Livemass gains/ha were highest at a stocking rate of 2,2 animals/ha and were 131,4 kg/ha under continuous grazing and 88,6 kg/ha under rotational grazing. Estimated mean maximum gains/ha were 0,78 kg/ha/day at a stocking rate of 2,5 animals/ha under continuous grazing and 0,55 kg/ha/day at a stocking rate of 1,7 animals/ha under rotational grazing. However, optimum economic stocking rates were estimated to occur below those where beef production/ha was maximum.     

Grazing methods and stocking rates for direct-seeded alfalfa pastures: III. Economics of alternative stocking rates for alfalfa pastures

A framework that permits estimation of economically optimal stocking rates for alternative economic parameters and alfalfa forage allowance was developed and applied to a controlled grazing experiment conducted with Holstein steers (243 kg) placed on direct-seeded alfalfa pastures in central Michigan. Responses of ADG to alternative levels of forage allowance (FA) were summarized by a quadratic function and the associated gains/hectare were calculated. The standard stocking rate (SSR; standard livestock units/ha) that maximized gain/hectare increased with FA and was greater than that which maximized ADG. Net returns to fixed resources(NRFR)/hectare were calculated for alternative SSR and economically optimal SSR were identified under various levels of herbage mass (kg/d). The SSR that maximized NRFR were between the SSR that maximized ADG and gain/hectare. Magnitude of the sale price discount for heavier calves, the slide, influenced the optimal SSR and the sensitivity of net return to SSR. The economically optimal SSR increased as the slide increased because animals stocked under higher SSR weighed less off pasture and therefore received a lower price discount.     

Patch grazing of Tall Grassveld by cattle after a spring burn

Patterns of herbage removal by rotationally stocked cattle (at a density of 4.85AUE ha^-1) on initially structurally homogenous Tall Grassveld were examined over a single season. Three unreplicated camps were stocked early (29 days), at the recommended '10-15cm' sward height (44 days), and late (80 days) after a spring burn. Temporal change in the spatial distribution of herbage in each treatment was described by intensive measurement of compressed sward height (CSH) with a disc pasture meter and analysed with parametric and spatial statistics. Grazing pressure at the start of the grazing was highest in the early graze, intermediate at the recommended, and least in the late graze treatment because of variation in initial herbage mass related to period of deferment after the burn. The early graze paddock was most spatially uniform and the late graze paddock the most uneven and patchy before grazing. Such initial conditions significantly affected subsequent herbage removal patterns: the greater the amount and spatial variability of herbage accumulated before grazing, the greater the chance for patches to develop through area-selective grazing. The early graze paddock was utilised non-selectively during the first two grazing periods but similar to other treatments, became patchier with time. Spatial pattern, a mosaic of short, intermediate and tall patches, peaked in late summer and was most pronounced in the late graze treatment. Intensive, early stocking after a burn is recommended for minimising intraseasonal development of patches and efficient use of high-quality forage available after a burn.     

Rotational and continuous grazing of sheep in the Inner Mongolian steppe of China

The aim of this study was to compare the effects of rotational and continuous grazing on herbage mass (HM), organic matter digestibility (dOM) and intake (OMI) and live weight gain (LWG) of sheep grazing on the inner Mongolian steppe, China at a stocking rate of 4.5 sheep/ha during the growing season. In the years 2005 and 2006, four 2-ha plots were used of which two were divided into four 0.5 ha paddocks each for rotational grazing, where sheep were moved each 10 days to the next paddock. The dOM was estimated from faecal crude protein concentration and OMI by oral administration of titanium dioxide. Herbage mass was similar in both grazing systems and dOM and OMI were higher (p < 0.05) at continuous grazing than at rotational grazing, but LWG did not differ probably because of extra energy expenditure for grazing and walking in a larger area. The dOM and OMI decreased (p < 0.05) with progress of the growing season and differed between years. Since precipitation during the growing season in both years was lower than the 30 years average which was probably the reason that positive effects of non-grazing periods on herbage regrowth and quality at rotational grazing could not occur, further studies are required in years with average precipitations before a final evaluation of these grazing systems can be made. Moreover, it seems necessary to quantify energy expenditure for physical activity of animals in grazing studies.