Sward dynamics of a smooth-stalked meadowgrass dominantwhite clover sward rotationally grazed by cattle and/or sheep

This experiment was carried out to study the responses of sward components (particularly white clover, Trifolium repens ) to grazing management in a natural sward dominated by smooth-stalked meadowgrass ( Poa pratensis ) syn. Kentucky bluegrass. Treatments during two grazing seasons (1989–90) were: cattle grazing alone (C); cattle grazing followed by topping (CT); cattle grazing followed by sheep grazing (CS); and sheep grazing alone (S). Mean target pre- and post-grazing herbage masses were 2200 and 1100 kg DM ha⁻¹, estimated by single-probe electronic capacitance meter. Sward component dynamics were monitored using turf dissections, marked white clover stolons, and ring-toss white clover leaf counts. Component and sward data for the C, CT, CS and S treatments respectively, were: number of white clover leaves m⁻², 1295, 1384, 1408, 900 (s.e. ± 108); number of leaves per growing point, 3·2, 3·4, 3·0, 2·8 (s.e. ± 0·2); herbage accumulation (t DM ha⁻¹), 5·16, 5·02, 5·87, 8·28 (s.e. ±0 08); rejected herbage (% pasture area) 39·7, 7·7, 16·0, 0 (s.e. ± 75); and annual net herbage production (t DM ha⁻¹) 3·39, 4·35, 4·99, 8·28 (s.e. ± 0.07). Swards grazed by sheep alone contained less white clover, but regrew quicker and produced more herbage than other treatments. Close topping or grazing by sheep following dairy cattle grazing decreased sward rejection by cattle. These treatments maintained more of the pasture in better condition for subsequent cattle grazing, resulting in greater net herbage production than where no post-cattle grazing treatment was used.     

Grazing cycle length and silage supplementation: effects on the performance of lactating ewes with twin lambs

Masham ewes, stocked at 20 ewes ha⁻¹, reared twins at pasture in 1979 and 1980 and were rotationally grazed around six paddocks. There were three lengths of grazing cycle (18, 30 or 42 d) and the ewes at pasture were either offered silage ad libitum (S) for 8 weeks of lactation or they were not supplemented with silage (N). By feeding silage, S ewes and lambs moved into greater herbage masses (3735 u. 3390 kg organic matter (OM) ha⁻¹), but there was little effect on net herbage accumulation (10.5 v. 10.0 t OM ha⁻¹) and herbage intakes per ewe were similar (2.31 v . 2.27 kg OM d⁻¹) over the 7-month grazing season. During the period of silage supplementation, total intake was 19% higher for S than N ewes, lamb growth rates were slightly higher (280 v . 273 g d⁻¹) and the ewes lost less weight (−78 v −96 g d⁻¹).
For 18-, 30- and 42-d grazing cycles respectively the herbage masses before grazing were 2825, 3620 and 4240 kg OM ha⁻¹; net herbage accumulations were 9.8, 10.4 and 10.6 t OM ha⁻¹; mean daily herbage intakes by each unit (ewe+lambs) were 2.22, 2.35 and 2.30 kg OM and lamb growth rates from birth to weaning at 20 weeks were 205, 204 and 204 g d⁻¹.
Frequent grazing of relatively light herbage masses or infrequent defoliation of heavier herbage masses made little difference to sward or animal performance. It is concluded that, at this stocking rate, different grazing cycles of 18, 30 or 42 d do not affect the performance of lactating ewes.     

Effect of stocking rate on the grazing behaviour and faecal output of lactating dairy cows

Information about the grazing behaviour and the return of dung to pasture by lactating dairy cows was collected from stocking rate experiments in northern Victoria. Grazing behaviour was observed for 24-h periods in mid-summer in two years. Grazing time increased as herbage allowance decreased to about 32 kg DM cow⁻¹ d⁻¹ but as herbage allowance decreased further grazing time also decreased. A herbage allowance of 32 kg DM cow⁻¹ d⁻¹ corresponded to a stocking rate of about 5.5 cows ha⁻¹. This effect of herbage allowance on grazing time may have been confounded by herbage mass, however. Rumination time of the cows increased by 003 h for each kg increase in herbage allowance while resting time was not affected by treatment.
The effects of stocking rate on some of the characteristics of faecal output were measured for a 3-d period in mid-summer. The number of pats deposited per cow daily declined by 0.66 for each unit increase in stocking rate. The fresh weight of dung also declined as stocking rate increased by 0.16 kg per unit of stocking rate. While the values for the amounts of dung deposited on the pasture by the cows at the lower stocking rates are similar to many of those reported in the literature, this study has quantified the way in which stocking rate may influence this in one instance. Furthermore, provided that some measure of herbage intake is made when measurements of dung excretion are performed, it is suggested that estimates of in vivo digestibility can be obtained.     

The utilization of N fertilizer, applied to perennial ryegrass/white clover pasture growing on a humus iron podzol in N.E. Scotland

Applications of N fertilizer (0.40, 80, 120 and 240 kg N ha⁻¹ year⁻¹ in dressings of 40 or 80 kg N ha⁻¹) were made to a perennial ryegrass/white clover ( Lolium perenne L. Trifolium repens L.) pasture growing on a humus iron podzol reclaimed from heather ( Calluna vulgaris L.) moor in 1982 and 1983. Where no N was applied, estimates of Ni fixation and mineralization were almost equal, being approximately 50 kg N ha⁻¹ year⁻¹ from each source. Apparent efficiencies of fertilizer use were generally low; for each dressing they ranged between –0·7 and 25·5 kg dry matter (DM)kgN⁻¹. Also, responses to N fertilizer were affected by previous dressings. The net N recovery in harvested herbage from application of 120 kg N ha⁻¹ year⁻¹ was 30 kg N ha⁻¹ year⁻¹.     

The intake and performance of cashmere goats grazing sown swards

An experiment was conducted to examine the relationships between sward surface height and the intake and liveweight gain of lactating female goats and their single kids and of 12-month-old castrated male goats continuously grazing grass pasture. Herbage intake was measured using the n -alkane marker technique. Goats grazed the experimental area from May to August at nominal sward heights of 3–4, 5–6, 7–8 and 9–10 cm. Sward heights achieved were variable but were consistently ranked in treatment order.
The herbage intake of females [57-140 g DM (kg LW^0.75)⁻¹ d⁻¹] and castrates [26-88 g DM (kg LW^0.75)⁻¹ d⁻¹] increased linearly with sward height over the range 3.2-11.0 cm. The liveweight change of females and castrates reflected the pattern of change in sward height.
The herbage intake of kids [17-41 g DM (kg LW^0·75)⁻¹ d⁻¹] was not related to sward height, but there was a consistent increase in liveweight gain with sward height from 98 to 129 g d⁻¹. The herbage intake of kids did not increase with age with means of 25–29 g DM (kg LW 0·75 d⁻¹ for kids aged 9–17 weeks.
There was evidence that all classes of goat selected green leafy material of high digestibility.     

The effect of stocking rate on a lamb production system with February-lambing ewes

Masham ewes were stocked at 12(L), 16(M) or 20 (H) ewes ha⁻¹, with 1·8 lambs per ewe on average, on two blocks (A and B) in both 1976 and 1977. Silage was offered at pasture to the ewes in early lactation and as stocking rate increased from 12 to 16 and then 20 ewes ha⁻¹, 47, 73 and 100 kg DM per ewe was consumed respectively. Silage was cut mainly in the autumn and 179, 100 and 9 kg per ewe was made for L, M and H respectively. More variation between treatments was measured in net herbage accumulation in summer than spring and 11·4, 10·0 and 9·7t DM ha ⁻¹ was grown over the whole season for L, M and H respectively as a mean of both years.
High intakes of herbage OM were measured with values up to 40 g per kg live weight for BL lambs in 1976. Rapid lamb growth was achieved. There were effects of stocking rate on lamb performance and for L, M and H the respective growth rates to 4 weeks were 266, 248 and 247 g d⁻¹; growth rates to sale were 274, 263 and 252 g d⁻¹; days to sale were 124, 126 and 129; mean carcass weights were 17·7, 17·1 and 16·7 kg. Most ewes lost weight in early lactation, especially AH and BH in 1976, but there were no stocking rate effects on ewe weight change in 1977.     

The combined use of fertilizer nitrogen and white clover on grazed ryegrass swards

A 1-year grazing experiment with dairy cows is described in which the milk yield and herbage intake from a sward of S23 perennial ryegrass alone receiving fertilizer N at an annual rate of 360 kg ha⁻¹ were compared with those from a ryegrass-white clover var. Blanca sward given a total N application of 180 kg ha⁻¹. Both treatments gave virtually the same total milk yield of about 12500 kg ha⁻¹ over a 20-week grazing season.     

Effects of concentrate supplementation and herbage allowance on the performance of grazing suckling lambs

An experiment was conducted to examine the effect of concentrate supplementation on the performance of suckling lambs while grazing at variable levels of herbage allowance. Twenty-four ewes suckling twin lambs were allocated 55 d after lambing between four grazing treatments (two levels of herbage allowance × two levels of supplementation) in a 2×2 factorial design. The sward consisted of Tall Fescue and was grazed rotationally.
Daily herbage organic matter (OM) allowances were 57.0 (H) and 38.5 (L) g OM kg LW⁻¹ above 1·5 cm cutting height. Lambs were either supplemented (S) ad libitum with high-moisture whole maize grain or unsupplemented (U).
Supplement intake during the 60-d grazing period was 16 kg DM and 17.5 kg DM respectively for LS and HS lambs. The effect of supplementation on lamb growth rate differed significantly between allowances: at the low allowance level, supplementation increased growth rate (287 g d⁻¹ vs 226 g d⁻¹), whereas it had no effect at the high level (277 g d⁻¹ vs 276 g d⁻¹). Growth rate of unsupplemented lambs was significantly reduced at the low level of allowance compared to the high level (226 g d⁻¹ vs 276 g d⁻¹). The effect of sward height on time spent grazing by unsupplemented lambs is described during the defoliation of a plot.     

Supplementary forage for grazing sheep. 1. Effects on lactating ewes and lambs

In two experiments, ewes in weeks 1–20 of lactation received either pasture only or pasture plus ad libitum conserved forage. Herbage height was maintained at 3·3–3·4 cm on both treatments by manipulation of stocking rate in the 24 plots (twelve per treatment) used for the experiment with additional ewes and lambs. In experiment 1, silage, which was of lower metabolizable energy (ME) and crude protein (CP) contents than the grazed herbage, was consumed at an average of 375 g dry matter (DM) ewe⁻¹ d⁻¹. In experiment 2 a strawmix, containing (g kg ⁻¹ freshweight) 480 g barley straw, 300 g concentrate and 220 g molasses, again with a lower ME and CP content than the grazed herbage, was consumed at an average of 165 g DM ewe ⁻¹ d ⁻¹. In both experiments ewes not receiving forage lost weight whereas those with forage gained weight and tended to have increased body condition scores. Offering silage or strawmix did not affect lamb liveweight gain or stocking rate.     

How does protein supplementation affect the selectivity and performance of Charolais cows on extensively grazed pastures in late autumn?

Management of beef cows grazing extensively grazed semi-natural pastures in temperate regions in late autumn can require supplements to be offered. The effects of supplementation with soya bean meal on the diet selected by Charolais cows and on their subsequent performance were examined for an 8-week period in late autumn in 2 years. Three groups of eight cows were compared: non-supplemented dry cows (D), non-supplemented (L) and supplemented (LS) lactating cows. The amount of soya bean meal supplement offered per cow was 250 g d⁻¹ in year 1 and 800 g d⁻¹ in year 2. Dietary choices were measured by direct observations and herbage intake was estimated in year 2. Supplementation affected neither diet selection (L: 0·42 vs. LS: 0·43 for the proportion of bites on green patches in year 1; 0·24 vs. 0·22 in year 2) nor daily organic matter intake of herbage (L: 15·6 vs. LS: 15·9 kg d⁻¹), which may have resulted from an adequate crude protein concentration of herbage. The higher total dry matter intake by cows offered the supplement reduced losses in live weight (L: −1212 vs. LS: −828 g d⁻¹; P  < 0·01) rather than increased milk production (L: 5·1 vs. LS: 5·0 kg d⁻¹). This may be linked to the low milk yield potential of the Charolais cows. The use of lactating cows rather than dry cows for pasture management in late autumn would increase the utilization of herbage but a reduction in liveweight losses of cows by supplementation is unlikely to be economic.     

Effect of supplementation on production by spring-calving dairy cows grazing swards of differing clover content

An experiment was carried out to examine the effect of supplementation on the performance of spring-calving dairy cows grazing swards of differing perennial ryegrass and white clover content. Seventeen heifers and sixty-four Friesian cows in their third to ninth week of lactation were turned out onto one of three pastures with different proportions of perennial ryegrass and white clover. Nine animals on each pasture received either 0, 2 or 4 kg d⁻¹ of a concentrate with a crude protein concentration of 180 g kg⁻¹ dry matter (DM). Prior to grazing, swards contained proportionately 0·01 (L), 0·15 (M) and 0·20 (H) of total DM as clover. During the experiment, grazing pressures were adjusted by movement of buffer fences to maintain compressed sward heights at 6 cm. Samples taken 26 and 68 d after the start of grazing showed little change in the proportion of clover in sward L (< 0·01 and 0·02 respectively), but convergence in the proportion of clover in swards M and L (0·08-0·16 and 0·10-0·15 respectively). Mean daily yields of milk, fat, protein and lactose increased significantly with increased clover content and, even without supplementation, daily yields were 25·4, 0·98, 0·73 and 1·09 kg respectively on sward H. Of the milk components, only protein was significantly increased by increasing sward clover content. The response in milk yield to supplementation was greater on sward L than on swards M and H.     

Herbage growth rates on heterogeneous swards as influenced by sward-height classes

The contribution of four classes of sward height to daily herbage growth rates of a heterogeneous sward in eight periods throughout a grazing season was investigated in two continuous cattle-grazing systems differing in intensity (moderate stocking rate: MC; lenient stocking rate: LC). At the beginning and end of periods of 12 to 28 d, the compressed sward height (CSH) was measured in exclusion cages at eighteen fixed points per cage to derive daily growth rates for the four classes of sward height. Stratified calibrations were made to relate sward height to herbage mass for each treatment in each period. Quadratic regressions described the relationship between herbage growth rate and initial CSH for each treatment in each period. For scaling up to the scale of the plot, CSH was measured monthly at 100 points per plot. Daily herbage growth rates declined from more than 100 kg dry matter (DM) ha⁻¹ d⁻¹ on both treatments at the beginning of the grazing season to 20 kg DM ha⁻¹ d⁻¹ or less, especially on treatment LC. This was due to the larger area covered by tall herbage on treatment LC than on treatment MC. On treatment MC, daily herbage growth rate was predominantly derived from short sward areas of up to 12 cm in height while sward areas taller than 12 cm contributed most to daily growth rates on treatment LC in early summer. The method used is considered suitable for estimating daily herbage growth rates of different classes of sward height in extensively managed pastures and can easily be adapted to deal with more heterogeneous swards than used in this study.     

Herbage potassium levels in a permanent pasture under grazing

Herbage potassium levels were measured in 1986 in a permanent pasture under continuous grazing with cattle and receiving 200 kg N ha⁻¹. In April, before grazing started, K concentration in the herbage was relatively uniform across the pasture, with a value of 1·9 ± 0·038% K in the herbage dry matter. In July, a significantly lower concentration of herbage K was found in the grazed areas of the pasture (1·8 ± 0·10%) compared with the level (2·4 ± 0·088%) found in the rejected areas of the sward. The difference between the grazed and rejected areas was similar in September, with 1·6 ± 0·087% and 2·2 ± 0·172% K, respectively, in the herbage dry matter. This result suggests that herbage growth in the grazed areas might have been limited by K supply and highlights the need for more information on the K requirements of grazed grassland.     

Some effects of herbage composition, as influenced by previous grazing management, on milk production by cows grazing on ryegrass/white clover pastures. 1. Milk production in early spring: effects of different regrowth intervals during the preceding winter period

Two experiments (1a and 1b) were carried out to examine the effects of differences in pre-grazing herbage mass and composition on milk production by cows grazing in early spring. Swards with high (5 · 1t DM ha⁻¹) or low (2 · 9 t DM ha-1) pre-grazing masses in early spring were created by either long or short periods of regrowth during the preceding winter.
The low-mass swards contained lower concentrations of grass stem and senescent material, but higher concentrations of clover, than the high-mass swards. Herbage from the low-mass swards was also more digestible.
Cows were offered common daily herbage allowances from both swards (26 and 22 kg DM cow⁻¹ in Experiments la and lb respectively). The cows grazing on the low-mass swards produced significantly greater yields of milk, milk fat and milk protein.
The results show that herbage from the lowmass swards was of higher feeding value for lactating cows in early lactation. The practical implications for milk production per cow and per hectare are discussed.     

Supplementary forage for grazing sheep. 2. Effects on weaned lambs

In two experiments weaned entire ram lambs were offered either pasture alone or pasture plus ad libitum conserved forage for 7–12 weeks during the finishing period. Herbage height was maintained at 3·2 cm on both treatments by manipulation of stocking rate in the twenty-four plots (twelve per treatment) used for the experiment. In experiment 1 silage, which was of lower metabolizable energy (ME) and crude protein (CP) content than the grazed herbage, was consumed at an average of 194 g DM head⁻¹ d⁻¹, providing approximately 40% of total DM intake requirements. In experiment 2 a strawmix, containing (g k g ⁻¹ freshweight) 450 g barley straw, 300 g concentrate and 250 g molasses and again with a lower ME and CP content than the grazed herbage, was consumed at an average of 57 g DM head⁻¹ d⁻¹, providing approximately 11% of total DM intake requirements. In both experiments stocking rate was increased by 20–25% by providing forage, but lamb growth rate was not affected.     

Effect of long-term changes in relative resource availability on dietary preference of grazing sheep for perennial ryegrass and white clover

Three replicate paddocks, each of 0·235 ha, containing adjacent monocultures of perennial ryegrass or white clover [50:50 by ground area, 6 cm sward surface height (SSH) at start of experiment] were continuously stocked with three yearling and four mature non-lactating, non-pregnant Scottish halfbred ewes for 12 weeks. Herbage intake, grazing behaviour and dietary selection were measured on seven occasions. Clover SSH declined rapidly over the first 5 weeks then stabilized at 1·2–1·6 cm, whereas perennial ryegrass SSH rose slightly initially, then declined gradually. Animals initially included proportionately c . 0·6 white clover in their diet but, by the end of the experiment, this had fallen to 0·3. Total daily herbage intake declined over the 12 weeks from 1·8 kg dry matter (DM) day^–1 at the start to 1·0 kg DM day^–1. Total grazing time increased from 561 min day^–1 to 649 min day^–1 at the end of the experiment. The results suggest that, despite overall herbage depletion and a greater depletion of white clover than perennial ryegrass as a result of the initial partial preference for white clover, the animals traded-off a reduced total intake and an increased grazing time in an attempt to maintain their initial preferred dietary composition.     

A comparison of buffer and partial storage feeding of a straw/concentrate mixture to grazing dairy cows

A straw/concentrate mixture was offered to set-stocked dairy cows over a 24-week period. The cows were offered grazed herbage only (G), or grazed herbage with a straw/concentrate supplement offered either for 45 min after each milking (B), or overnight (P). The overnight treatment involved housing the cows between afternoon and morning milking. The straw/concentrate mixture contained 0·33 long barley straw, 0·28 barley, 0·12 soya bean meal, 0·25 molaferm and 0·02 minerals. During the first 8 weeks of the experiment an average of 2·25 kg of concentrate were fed, and from weeks 9–24, 2·0 kg of concentrate were fed.
The feeding of the straw/concentrate mixture led to a decrease in estimated herbage dry matter (DM) intake, particularly for treatment P. Estimated total DM intakes were increased throughout the experiment by offering the straw/concentrate mixture. However, total metabolizable energy (ME) intakes were only increased in mid-and late season.
Milk yield was higher in early season for treatment G; 28·1 kg d⁻¹ compared to 26·8 kg d⁻¹ and 25·5 kg d⁻¹ for treatments B and P respectively. In late season the cows in treatment G had lower milk yields; 13·3 kg d⁻¹ compared to 15·5 kg d⁻¹ and 16·8 kg d⁻¹ for treatments B and P respectively. Milk fat content was increased in early season in treatment P, and milk protein content tended to be reduced throughout the experiment for cows offered the straw/concentrate mixture overnight. Over the whole experiment there were no differences in yield of milk solids.     

Seasonal changes in the crude protein concentration of mixed swards of white clover/perennial ryegrass grown without fertilizer N in an organic farming system in the United Kingdom

Changes in the crude protein (CP) concentration of white clover and perennial ryegrass herbage from a mixed sward were determined on six sampling dates from May to October in each of 2 years. The swards were grown without fertilizer N in an organic farming system and continuously grazed by dairy cows during the grazing season. The annual mean contents of white clover in the dry matter (DM) of the sward were 272·3 and 307·0 g kg⁻¹ in Years 1 and 2. The mean CP concentrations of the white clover and perennial ryegrass herbage were 251·6 and 151·9 g kg⁻¹ DM in Year 1 and 271·9 and 174·0 g kg⁻¹ DM in Year 2 respectively. The CP concentration of the white clover increased significantly during the grazing season from 220·0 to 284·1 g kg⁻¹ DM in Year 1 and from 269·0 to 315·5 g kg⁻¹ DM in Year 2. In the perennial ryegrass herbage the CP concentration increased from 112·2 to 172·6 g kg⁻¹ DM in Year 1 and from 142·7 to 239·5 g kg⁻¹ DM in Year 2. The rate of increase during the season in the CP concentration of the perennial ryegrass herbage was similar to the rate of increase recorded in the white clover herbage.     

Assessment of contrasting perennial ryegrasses, with and without white clover, under continuous sheep stocking in the uplands. 3. Herbage production, quality and intake

Herbage characteristics were monitored over 3 years (1985–1987) in three perennial ryegrass ( Lolium perenne L.) varieties as grass/only (200 kg N ha⁻¹) and grass/clover ( Trifolium repens L.) (75 kg N ha⁻¹) swards when continuously stocked with sheep. Although mean total annual herbage production was similar from the grass varieties, growth of Aurora, a very early-flowering variety, was higher than that of Aberystwyth S23 and Meltra (tetraploid) late-flowering types in spring. Herbage production from grass-only swards was 15% higher than from grass/clover swards.
In vitro organic matter digestibility (OMD) of Aurora and Meltra was 34 g kg ⁻¹ and 26 g kg ⁻¹ higher ( P < 0·01) than that of S23. Averaged over varieties, the OMD of grass/clover was 25 g kg ⁻¹ higher ( P < 0·05) than grass-only during the post-weaning period. Individual lamb digestible organic matter intake (DOMI) was 22% higher ( P < 0·05) on grass/clover than on grass-only during this period. Water-soluble carbohydrates content of Aurora was 42% higher ( P < 0·001) than that of both Meltra and S23.
Herbage characteristics were related to lamb performance reported previously. Lamb production was positively correlated with DOMI. However, the magnitude of differences in lamb performance between treatments was much greater than the extent of differences detected in herbage characteristics.     

The liveweight gain of Limousin × Friesian heifers grazing perennial ryegrass/white clover swards of different clover content and the effects of their grazing on sward botanical composition

An experiment was carried out in 1992 and 1993 to examine the effect of white clover content of perennial ryegrass/white clover swards on the performance of Limousin × Friesian heifers. Swards with low (L), medium (M) and high (H) white clover contents were established and managed by continuous variable stocking. A compressed sward height of 5·5 cm was maintained using a buffer fence to vary plot areas, with herbage surplus to grazing requirements cut, removed and yields measured. The mean white clover proportions for treatments L, M and H were 0·02, 0·19 and 0·18 in 1992 and 0·13, 0·16 and 0·31 in 1993 respectively. White clover contents of the swards reached a maximum in August and September, and differences between treatments diminished. There was no significant difference between treatments in the content of white clover in the swards in autumn 1993.
Liveweight gains of heifers increased asymptotically with increasing white clover content of the sward. Below a white clover herbage mass of 300 kg DM ha^–1, there was little effect on liveweight gain, which was 0·70 kg day^–1 over the grazing season. Between 400 and 450 kg DM ha^–1 white clover, liveweight gains were 0·85–0·90 kg day^–1. While clover content of the sward did not significantly affect utilized metabolizable energy output; the mean output over the grazing season in the two years from liveweight gain and herbage yield was 78 GJ ha^–1. It is suggested that, using this grazing system, white clover reached an equilibrium with a mean herbage mass of about 400 kg DM ha^–1 over the grazing season.