Short Swards Research Articles

Winter Field Use by the European Starling Sturnus vulgaris: Habitat Preferences and the Availability of Prey

A regular census of an Oxfordshire farm, U.K., showed that the resident Starlings Sturnus vulgaris preferred to feed in established pasture fields. Fields which were closer to the daytime roost, provided feeding areas further from hedges, and had shorter swards were particularly preferred. The Starlings' habitat preferences could also be explained in terms of the availability of prey. This was quantified via the foraging behaviour of individual birds allowed to forage in small enclosures in a sub-sample of the fields available to the flock. The experimental birds' prey capture rates in each of the fields were significantly correlated with the observed flock foraging densities. This was a prey-specific effect: although the birds could have obtained a higher energy

Effect of herbage rejection by steers on white clover (Trifolium repens) branching and development in continuously stocked grass–clover swards

SUMMARYThe proportion of sward area rejected for grazing under different stocking intensities in grass-white clover (Trifolium repens L.) swards continuously grazed by steers toconstant sward height was determined and the effect of these areas on clover stolon developmentwas investigated.In a randomized block field experiment, grazing treatments imposed from 1988 to 1991 comprised target sward surface heights (SSH) of 5, 7 or 9 cm from April to July followed by 7 or 9 cm from July to October (i.e. six treatments). The percentage area rejected was higher in 9 cm than in the shorter swards, the proportion of the total areas rejected increasing generally over the year. Within the rejected areas in spring the number of branches on the main axes of white clover plants was only 17% and the mean number of nodes per branch was 14% of those in grazed areas. Corresponding percentages in summer in rejected areas were 56 and 46% compared with grazed areas.In a glasshouse experiment involving stolons grown for 18–21 days, the difference between those from grazed and rejected areas in branch number per stolon and mean node number per branch was much reduced. Branching and rate of branch development (node number) were slower in stolons maintained under dark conditions.Mean growing point density over six sampling dates from summer 1990 to autumn 1991 was significantly higher in the 5 cm than in the 9 cm spring SSH treatment. Although rejected areashad only 34% of the growing point density of grazed areas in autumn, the latter comprised the majority of the total area in most sward height treatments and so reduced the overall effect of rejected areas on growing point density.

The effect of surface height of swards continuously stocked with cattle on herbage production and clover content over four years

AbstractThe long‐term influence of sward height from April to July (Phase 1) and from July to early October (Phase 2) on total herbage and white clover production was measured over four years (1988–1991) as herbage accumulation. A subsidiary experiment to determine the influence of leaf area index (LAI) on gross canopy photosynthesis was conducted to aid interpretation of growth from herbage accumulation data. Target sward heights in 0·5 ha plots in two blocks were 5,7 or 9 cm in Phase 1 and 7 or 9 cm in Phase 2, although mean actual heights per phase were slightly higher. Net herbage accumulation (NHA) was measured within mobile exclosure areas over successive two‐week intervals. Gross photosynthesis was measured in circular turves removed from the trial area representing a range of LAIs with an at least reasonable clover content. Despite wide differences in mean sward height and herbage mass, NHA and net clover accumulation for a given phase were not generally affected by treatments. Positive effects of grazing at 5 cm in Phase 1 on NHA and clover accumulation later in the year, and of grazing at 7 cm in Phase 2 on NHA in the following spring were sometimes apparent. Gross canopy photosynthesis (g CO2 m−2 h−1) at 1500 μE m−2 s−1 and 18–21°C was linearly related to LAI described by 1·003 + 1·165 LAI over the LAI range 0·7 to 4·5. Total herbage and clover growth, interpreted from NHA by a previously described model, was predicted to be marginally lower in shorter swards. Similarity in NHA and clover accumulation between treatments was considered to be because of lower senescene and decomposition, and a higher proportion of new tissue being assigned to lamina growth, despite lower LAI and gross photosynthesis in the shorter swards. It was concluded that stocking intensity in swards continuously stocked with cattle did not have a strong influence on net total herbage and clover growth.

The effect of genotype × environment interactions on biological efficiency in beef cows

AbstractAn experiment was conducted to examine the response of three genotypes of beef cows to contrasting levels of nutrition supplied from grazed pasture. Twenty-two Hereford × Friesian (HF), 20 Aberdeen Angus × Friesian (AF) and 24 Welsh Black (WB) spring-calving beef cows with their Charolais-cross calves were used in 4 years consecutively. During the summer grazing period they grazed permanent pasture maintained at either 4 to 5 cm (short) or 7 to 8 cm (tall) sward surface height. Sward height treatment significantly (P < 0·001) affected cow and calf live-weight gain (0·498 v. 0·041 (s.e.d. 0·0405) kg/day and 1·12 v. 0·90 (s.e.d. 0·021) kg/day for cow and calf live-weight gain on the tall and short swards respectively). The live-weight gains of the HF and WB cows were similar, but the AF cows gained less weight on the tall sward and lost weight on the short sward. Calf live-weight gain reflected cow milk yield, with the calves from HF and AF cows having similar live weight gains (1·06 and 1·02 kg/day respectively) and those from WB cows having lower gains (0·95 kg/day; P < 0·001). The effect of sward height on calf live-weight gain was greatest in the WB-born calves because of the lower milk yield from WB cows. Body chemical composition changes of cows were predicted from live weight and body condition score, using prediction equations derived from separate groups of cows which were slaughtered at a range of body compositions for determination of chemical composition. Energy balances, calculated from changes in chemical composition, showed the AF cows to have the lowest energy balances with the WB cows the highest. Calculation of energetic efficiency and land use efficiency of weaned calf production taking account of annual food requirements indicated that the HF cows were most efficient, and the WB cows least efficient. The effect of increasing nutritional environment (as represented by sward height treatment) was such as to increase energetic efficiency for all genotypes, but land use efficiency was increased for HF and AF cows, and decreased for WB cows. These results indicate the factors such as size of cows, milk yield potential and pattern of nutrient partitioning can influence energetic land use efficiency of weaned calf production, and that important interactions between genotype and nutritional environment can occur in different measures of efficiency.

Utilization, diet and diet selection by brent geese Branta bernicla bernicla on salt‐marshes in Norfolk

The diet and utilization by brent geese of two plant communities (Limonium/Armeria marsh—a short sward community in the upper mid salt‐marsh and composed of several species, and Salicornia marsh—a community of the lower salt‐marsh dominated by Salicornia europuea agg. and Aster tripolium) were studied on the north Norfolk coast. The biomass on these communities was highest in autumn and declined markedly in November owing to the senescence and die‐off of the succulent species. This decline was not significantly precipitated by the grazing of the geese but coincided with their switch to inland habitats where the biomass m‐2 and total food available on fields of winter wheat and grassland within the population's home range was 20–30 times greater. Brent geese continued to graze salt‐marsh at a low intensity through the winter, feeding largely on Puccinellia maritima. In spring they returned largely to Limonium/Armeria marsh where they significantly reduced the regrowth of Puccinellia maritima.The main plant species ealen was Puccinellia maritima, especially in mid winter. Salicornia maritima agg. leaves and seeds formed much of the diet in autumn, whereas Triglochin maritima, Plantago maritima and Aster tripolium were important foods on Limonium/Armeria marsh in spring. All these species were selected at some part of the year. Selection was related to the proline (an imino acid used by salt‐marsh plants as an osmoregulator) and chloride content and avoidance related to tannins. Two species which contained condensed tannins. Limonium vulgare and Armeria maritima, were rarely eaten. As well as being a nutrient, proline may help to neutralize the effects of tannins in the diet if incorporated into proline‐rich proteins.

Production responses by cows to grass-clover swards maintained at different heights with or without concentrate supplementation

Clements, Huckle and Wilkins (1991) reported that milk yield did not differ significantly between cows grazing grass-clover swards with compressed sward heights maintained at either 4.5 or 6 cm in early season. However, cows grazing the shorter sward produced milk with a lower protein concentration. The feeding of 4 kg concentrates/day resulted in an increase in milk yield at both sward heights but there was no effect on milk constituent concentrations. The present experiment was designed to investigate the effect of a wider range of sward heights and their interaction with concentrate supplementation.Forty eight, multiparous, Holstein Friesian cows with a mean calving date of 21 March were continuously stocked on mixed grass-clover swards. The cows were blocked by calving date, parity and milk yield and randomly allocated to one of six treatments, 0 (U) or 4 kg concentrate supplementation (S) with swards maintained at 4, 6 or 8 cm compressed sward height. Sward heights were maintained by adjusting the grazed area. The swards were permanent pastures which had received no fertilizer nitrogen.

Mitigation of low stream pH and its effects on salmonids: G. L. Lacroix, Environmental Pollution, 78(1–5), 1992, pp 157–164

The winter grazing intensities of brent geese Branta bernicla, pink-footed geese Anser brachyrhynchus, and white-fronted geese A. albifrons, and the breeding densities of lapwing Vanellus vanellus, redshank Tringa totanus and snipe Gallinago gallinago, were related to the environmental characteristics of 81 fields within an area of coastal grazing marshes on the north Norfolk coast. Those fields grazed most intensively by geese in the winter supported lower densities of breeding waders in the summer than fields that were rarely grazed by geese. Lapwing, redshank and snipe all tended to occur in higher breeding densities on the wettest fields (characterised by large areas of surface water and Juncus spp., high soil moisture content and high water levels in field drains and adjacent ditches) and where vegetation was short (6–14 cm) in late March. The highest grazing intensities of geese were recorded on fields close to the roost sites with brent and grey geese rarely using fields at distances of greater than 5 km and 8 km from their respective roosts. The two species of grey geese tended to use those fields that were drier and located at greater distances from sources of disturbance with slightly longer (though still relatively short) swards than those used by brent geese. In a subset of the fields close to the roost site, brent geese used fields more intensively if they had been heavily grazed by livestock, had a short sward in October and if the soil was relatively impenetrable. The results suggest that waders, brent geese and, to a lesser extent, grey geese select areas of grassland with short vegetation, but that the former favour areas where the water table is higher than in those areas favoured by geese. It is suggested that this potential conflict may be relatively easily resolved either by temporal differences in management regimes, whereby water levels are raised in spring and summer and lowered in winter, or spatial differences in which some fields are managed for geese, preferably those close to the roost, and others for waders.

The response of spring-born suckled calves to the provision of supplementary feeding when grazing two sward heights in autumn

AbstractAn experiment was conducted to measure the response of spring-born suckled calves to supplementary feeding when they grazed, with their dams, on swards of different heights in the autumn. Two swards were maintained at mean heights of either 5·8 cm or 9·0 cm, and calves were offered 0, 0·76 or 1 -51 kg organic matter (OM) per day of a commercially available supplement for a period of 60 days until weaning. Supplement intakes by the calves grazing the taller sward increased throughout the 60-day period, but did not exceed 0·75 kg OM per day. There was no response in terms of calf live-weight gain to the provision of supplement on the sward maintained at 9·0 cm. On the shorter sward, intake of supplement increased at a greater rate and reached 0·75 kg OM within 3 weeks. Maximum intake by those calves offered 1·51 kg supplement OM per day was 1·25 kg OM per day. The provision of supplementary feeding when mean sward height was 5·8 cm resulted in a significant increase in calf live-weight gain (P < 0·05), although supplementary feeding did not fully compensate for the reduction in milk and herbage intakes because of partial substitution of supplement for herbage. During the winter after weaning the calves that had previously grazed the shorter sward showed increased live-weight gain compared with those that had previously grazed the taller sward but prior supplementary feeding was without significant effect in this group.

Bite Dimensions and Herbage Intake by Cattle Grazing Short Hand‐Constructed Swards

AbstractThe objectives of this study were to contribute to the understanding and quantification of the effect of sward structure on the ingestive behavior and intake of livestock. Hand‐constructed swards of approximately 0.43 m2 were used to determine the bite dimensions, bite weight, and short‐term intake rate of steers (Bos taurus L.) grazing short swards. Swards were constructed of leaf blades of Paspalum dilatatum Poir. at homogeneous heights of 0.04, 0.06, 0.08, and 0.10 m and heterogeneous heights with means of 0.06 and 0.10 m at two leaf densities. Treatments were replicated using three 4‐yr‐old steers. Bite depth (B) was defined as the initial sward height (H) minus the mean residual height of grazed leaves. Bite area (A) was defined as the surface area represented by the mean number of leaves grazed per bite. Leaf density had no effect on bite dimensions. Linear regression of B on H and linear regression of A on H explained 99% and 89% of the variance, respectively. Mean bite weight ranged from 0.053 to 0.807 g. Correlation of measured bite weight with the product of the measured B, A, and bulk density yielded a coefficient of determination of 0.97. Mean intake rate ranged from 131 to 1473 g h−1. Bite weight accounted for 93% of the variance of intake rate. Bite dimensions on heterogeneous swards were similar to those on homogeneous swards, though by different mechanisms. The importance of biting overlap, leaf insertion in the mouth, and tongue sweeping are discussed in relation to mean bite dimensions and weight.

Maximizing Energy Retention in Grazing Ruminants

SUMMARY (1) Costs of locomotion are frequently ignored in models determining the optimal diet of free-ranging ungulates. In order to determine whether such omissions are justified, the relationship between bite size and distance travelled per day is investigated in several wild species of ruminant grazing natural pastures in the Serengeti National Park, Tanzania. (2) The distance travelled to obtain a gram of food rises exponentially as bite size declines. Animals feeding on short swards have small bite sizes, but it is suggested that animals feeding selectively on course grasslands would also have small bite sizes. It is shown that the heat production in locomotion of selective animals can form a large fraction of the daily intake of metabolizable energy. (3) A simple model of the energy exchange in free-ranging ruminants is developed incorporating parameters of diet quality and heat production. The model applies to pastures which do not set a limit to the daily intake of dry matter. The optimum level of selection for high quality constituents in the grass sward is found by determining the conditions in which energy retention (net energy) is at a maximum. (4) For any particular pasture, the optimum level of selection is found to be strongly dependent on the cost of locomotion per day and on the difference between the metabolizable energy concentration of high and low quality constituents, weakly dependent on the average quality of forage, and independent of the ruminant's resting metabolic rate. (5) The model predicts that the optimum level of selection by large grazing herbivores will be lower than that of smaller animals. This is because large herbivores gain more from digesting low quality constituents due to their ability to digest cell walls, and also because the foraging costs of large animals are higher.

A note on the post-weaning performance of autumn-born suckled calves

Thirty-nine Charolais × (Hereford × Friesian) autumn-born calves, whose dams had been given either 92 or 63 MJ metabolizable energy per day during winter and subsequently grazed at two sward heights, either 4-8 (short) or 7·6 (tall) cm from 6 May until weaning on 3 July in a factorially designed experiment, were used to examine the effect of pre-weaning performance on post-weaning growth rates. Following weaning the calves grazed as one group for a period of 76 days. There was no effect of winter treatment on postweaning performance. From weaning until 76 days later there was a significant (P < 0·01) effect of pre-weaning sward height on live-weight gain (0·94 and 0·69 kg/day for the calves from the short and tall swards respectively), so that the 41 kg liveweight difference at weaning was reduced to 22 kg (P > 0·05) with compensatory growth occurring independently of the height of the sward grazed.

The preference of dairy cows for combinations of high riegrass and high clover feeds and the effects on production

Supplementary forage is frequently fed to grazing cows to overcome pasture shortages. It is particularly Important for cows grazing a high clover Sward because of the need to maintain a short sward that will encourage high clover contents. This experiment compared high clover and high ryegrass silages and hay as supplements for cows grazing high clover or high ryegrass pastures.

Effects of sward surface height on the performance of continuously stocked spring‐calving beef cows and their calves

AbstractThe response of continuously stocked spring‐calving beef cows and calves to a range of sward surface heights was determined. Mean sward heights of 4‐5, 60, 70, 91 and 11‐0 cm (treatments A to E respectively) were maintained from mid‐May to mid‐August (Period 1) and treatments C, D and E continued until the end of September (Period 2), during which time mean sward heights were 5‐4, 7‐8 and 9‐2 cm respectively. Hereford x Friesian or White Shorthorn‐x Galloway cows with their Charolais‐cross calves were used, with 9, 6, 6, 5 and 9 cows on treatments A to E respectively. During Period 1 the mean live weight gains of cows were‐0‐52,‐005,0‐32,075 and 0 40 (s.e.d. 0167) kg d−1 on treatments A to E respectively and during Period 2.‐0‐31, 057 and 059 (s.e.d. 0153) kg d−1 for treatments C, D and E respectively with maximum cow liveweight gain at sward heights of 8 to 10 cm. Calf liveweight gains were 0 88,091, 098, 1 04 and 1‐06 (s.e.d. 0068) kg d−1 in Period 1 for treatments A to E respectively and 098, 1‐22 and 1 35 (s.e.d. 0067) kg d−1 in Period 2 for treatments C, D and E. The percentage of area infrequently grazed was generally less than 20% on treatments A to D, but on treatment E it was more than 40% for 6 weeks after turnout and thereafter remained between 20 and 40%. Maximum calf liveweight gain per hectare was achieved on the shorter swards, but maximum total liveweight gain of cows and calves per hectare occurred on treatment D. It is concluded that for maximum cow and calf performance on continuously stocked pastures, sward height should be maintained at no more than 8 cm in spring and early summer and then increased to 9 to 10 cm later in the grazing season.

Effect of changing grazing severity on the composition of perennial ryegrass/white clover swards stocked with beef cattle

AbstractDuring an experiment in which the height of mixed perennial ryegrass/while clover swards was maintained throughout the season at 3 or 7 cm (S and T, respectively), or were maintained al those heights until 30 June then changed (ST and TS), a limited study was made of the effects on the population densities and masses of the two species. During the earlier part of the season the short swards (S and ST) developed higher tiller and stolon growing point (sgp) densities, but with a reduced mass of ryegrass, principally of the pseudostem fraction, than the tail swards (T and TS). Thiere was little effect of sward height on the mass of clover. Whilst there was a general tendency for tiller and sgp densities to increase during the latter part of the season, tiller density increased greatly where sward height was reduced (TS) and both tiller and sgp densities were reduced where sward height was allowed to increase (ST). Changing sward height, whilst limiting the accumulation of dead grass material (TS), allowed grass leaf and dead masses to increase (ST), and adversely affected the increase in the clover component, principally of stolon material, in both ST and TS.

The Allometry of Food Intake in Grazing Ruminants

(1) A simulation model of grazing mechanics in ruminants shows that, due to the allometric relations of bite size and metabolic requirements to body size, small animals are able to subsist on shorter swards than large animals. (2) The density of nutrients in the grazed horizon of the modelled swards markedly affected the ability of animals of a given body size to satisfy their energy requirements. (3) By extension, the allometric relationships would be expected to apply in selective grazing and browsing species in their choice of food items of different size and nutrient content. (4) The results support the argument that sexual segregation and habitat choice of dimorphic species is an effect of scramble competition for limited resources, the males thus being excluded from mutually preferred swards. (5) The model provides an explanation for two interspecific phenomena amongst grazers: grazing succession and grazing facilitation.

The nature of the relationship of electronic capacitance meter readings to pastures on offer in short swards

AbstractThe residual standard deviations and distribution of residuals around five models were used to investigate the relationship between recordings from an electronic pasture probe and dry matter harvested from annual pastures (predominantly subterranean clover) at low levels of green feed on offer. Pasture material harvested was that considered to have the greatest influence on the probe i.e., within 5 cm of it.The following conclusions were drawn. When measuring short dense green pastures yielding up to 3000 kg dry matter ha‐1 the model best describing the relationship is a split line. Curvilinear models are better than a linear model; however, both single linear and curvilinear models give biased estimates particularly near the middle and at the lower end of the range.The best fitted model is discussed in terms of the structure of the sward and the probe.

The effect of sward height on beef cow performance and on the relationship between calf milk and herbage intakes

ABSTRACTGroups of 12 spring-calving cows and their calves were allocated to each of three continuous grazing treatments: cows and calves grazed a 4- to 5-cm sward (LI), cows grazed a 4- to 5-cm sward and their calves grazed an 8- to 10-cm sward (Lh) and cows and calves grazed an 8- to 10-cm sward (Hh). In each case cows and calves grazed separately. Sward height had a large effect on both cow and calf performance and intake. The short swards reduced cow herbage intake proportionately by 0·2 compared with that of the taller sward. Cow live-weight gains were −0·60, −0·59 and 0·42 (s.e.d. 0·103) kg/day on treatments LI, Lh and Hh respectively while calf live-weight gains were 0·80, 0·95 and 1·14 (s.e.d. 0·040) kg/day. Calf milk intakes were 7·05, 5·78 and 9·34 (s.e.d. 0·508) kg/day respectively while daily herbage intakes were 17·2, 22·0 and 19·8 (s.e.d. 1·35) g organic matter per kg live weight for treatments LI, Lh and Hh. There was a negative association between calf herbage and milk organic matter intakes in the treatments where the calves had access to a more generous sward height (treatments Lh and Hh), the regression coefficient being −0·89 (s.e. 0·381), indicating the calves' ability to increase herbage intake in response to a reduction in milk intake. On the LI treatment there was no significant relationship between milk and herbage intakes. The ability of grazing suckled calves to compensate for a reduction in milk intake is thus dependent on sward conditions, and may also depend on herbage digestibility. The increase in herbage intake cannot however compensate fully for a restriction in milk supply.

The effect of winter food level on compensatory growth of weaned, suckled calves grazed at two sward heights

ABSTRACTTwo experiments were conducted with weaned, suckled calves to investigate the effect of feeding level during the post-weaning winter on their subsequent performance when continuously grazed on pasture maintained at two sward heights. Low, medium and high levels of winter feeding resulted in winter live-weight gains of 0·31, 0·58 and 0·79 (s.e. 0·027) kg/day (P < 0·001) during the 152-day winter in experiment 1 and 0·44, 0·69 and 0·84 (s.e. 0·029) kg/day (P < 0·001) for 189 days in experiment 2. During summer (93 days in experiment 1 and 87 days in experiment 2) there was a significant effect of winter food level on performance when live-weight gains were 1·10, 1·02, 0·87 and 1·35, 1·23 and 1·19 (s.e. 0·060) kg/day for the low, medium and high winter food levels on the short and tall swards respectively in experiment 1 (P < 0·01) and 0·86, 0·66, 0·51 and 1·26, 1·18 and 0·91 (s.e. 0090) kg/day in experiment 2 (P < 0·001). The cattle showing compensatory growth had higher herbage intakes and it is postulated that this occurred because of a negative association between body fat and herbage intake. Sward height had a large positive effect on herbage intake and live-weight gain and it is concluded that for maximum intake on ryegrass swards, herbage height should be at least 8 cm. Lower levels of winter live-weight gain delayed the time to slaughter, but allowed cattle to achieve heavier carcass weights at a fixed level of fatness.It is concluded that there is no single optimum winter food level for weaned, suckled calves but that the choice will depend upon several factors, including availability of winter and summer food resources, the length of the winter feeding period, the desired date of slaughter and type of carcass to be produced.

The fitting of frequency distributions to height measurements on grazed swards

AbstractHerbage height was measured in ryegrass/white clover (Lolium perenne/Trifolium repens) swards grazed by cattle using the rising plate meter or the sward stick. Ordinary single normal and double normal distributions were fitted to the data obtained. After the first 6 weeks of continuous grazing the double normal distributions fitted data for the taller swards better than the single normal distribution did, but for a short sward there was no improvement. There was no improvement due to the use of the double normal distribution with data for swards grazed by sheep.

Defoliation of ryegrass‐dominated swards by sheep

AbstractPatterns of defoliation in perennial ryegrass‐dominated swards were examined in two experiments. In Experiment I measurements were made on four swards after a single overnight grazing. In Experiment 2 observations were made repeatedly on marked tillers in two continuously stocked swards which were grazed down over a 24‐d period. In both experiments the chance of defoliation was related to lamina height both within and between age classes. Lamina angle was measured in Experiment 2 and within age classes the chance of defoliation was also independent of lamina angle. In Experiment 1 tillers most frequently had both of the two youngest laminae grazed; in Experiment 2 tillers with only lamina 1 grazed occurred most frequently, but defoliation of the two youngest laminae was again common.The different frequencies of grazing of the different classes of laminae is interpreted as being a function of their frequency of occurrence within the grazed layer at the top of the sward. The pseudostem apparently restricted the depth of the grazed layer in the very short swards of Experiment 2.Grazing behaviour in relation to sward structure and the patterns of defoliation and their implications for herbage production are discussed.