Spear Grass Research Articles

Leaf water potentials of pasture plants in a semi-arid subtropical environment

Leaf water potentials (�1) were measured on pasture plants at the Narayen Research Station in southern Queensland. The main findings were: 1. There were marked differences between species in the value of �1, measured during drought. Lucerne (Medicago sativa cv. Hunter River) and buffel grass (Cenchrus ciliaris cv. Biloela) usually showed a lower (i.e. more negative) �1 than Siratro (Macroptilium atropurpureum cv. Siratro), when they were grown together in a mixed pasture. Siratro seemed to possess a useful degree of drought avoidance. High drought resistance was observed in buffel grass; this was attributed to its tolerance of water stress. Green panic (Panicum maximum var. trichoglume cv. Petrie) was found to have as low a �1 as lucerne during drought when the two species were grown with Siratro in a mixed pasture. 2. The plants were under severe water stress before all the available water was removed from the deeper soil horizons. 3. �1 was lower in nitrogen-fertilized buffel grass or spear grass (Heteropogon contortus), than in the corresponding unfertilized controls. 4. The vapour-exchange and dye-marker densiometric methods gave different values for �1 in buffel grass, green panic and Siratro; the vapour exchange technique recorded lower, i.e, more negative figures than the other method when the plants were under severe water stress. The two methods gave similar values for lucerne. The relation between the values obtained for buffel grass by the two methods was affected by nitrogen fertilization. The reaction of sown pasture plants to drought at Narayen is discussed.

Comparison of the diets of goats and sheep on a Casuarina cristata - Heterodendrum oleifolium woodland community in western New South Wales

The diets of sheep and feral goats grazing a semi-arid woodland in western New South Wales were assessed using oesophageal fistulated animals. The diet of the goats consisted largely of browse, with the leaves of Heterodendrum oleifolium (rosewood) a consistent component, although a large proportion of herbaceous material (mainly Bassia spp.) was eaten on occasions. The sheep showed a preference for the pasture species Stipa variabilis (spear grass) and Bassia spp. (copper burrs). When these plants were not available they were replaced in the diet by a higher proportion of browse, mainly of the tree Casuarina cristata (belah). Nitrogen contents of the diets ranged from 1.6 per cent to 3.0 per cent, with that of the goats generally being greater than that of the sheep. In vitro digestibility data indicated comparable values for both animal species, with lower values occurring under higher stocking pressures. The woody weed Eremophila sturtii (turpentine) was ignored by both sheep and goats at all stocking rates. Another weed shrub Cassia eremophila var. platypoda (punty) was browsed very sparingly. This indicates that the use of goats in an attempt to eliminate established stands of these species is unlikely to be successful at low to moderate stocking rates.

Reproductive activity in beef heifers following post-weaning feeding on spear grass hay alone or with supplements

A group of 24 heifers was weaned, divided into three groups of eight and pen-fed during the dry season in north Queensland (Lat. 18�S). One group, which received poor quality native pasture hay only, lost body weight. Another group, which received in addition a small portion of legume hay in the diet, gained body weight slowly. The third group received a further addition of legume hay plus cereal grain and gained body weight more rapidly. During the following wet season all animals were allowed to graze and the occurrence of oestrus was noted. Only two heifers in the poorly fed group exhibited oestrus. Six heifers in each of the other groups exhibited oestrus, but those that were better fed exhibited oestrus cycles for a longer period. Following this grazing period, all animals were slaughtered and analysed for the major chemical components.It was concluded that only small improvements in nutrition need be made during the tropical dry season to increase protein and energy intake sufficiently to support body weight gain. During subsequent grazing marked changes in oestrous activity can result from such improvements. The onset of oestrous appeared closely related to body fat content.

The utilization and excretion of sulphur in cattle fed on tropical roughages

The effect of additions of sulphateh to the diet of cattle given tropical spear grass (Heteropogon contortus) and Townsville stylo (Stylosanthes humilis) was studied in three experiments. In one experiment there was a small increase in the digestibility of dry matter, but the intake of feed was not affected. The concentration of volatile fatty acids in ruminal liquor from cattle offered spear grass was increased by supplemental sulphate; there was a concurrent small decrease in the proportions of propionic and isovaleric acids. Excretion of faecal sulphur varied with the intakes of total sulphur, organic matter, and digestible organic matter, while urinary sulphur excretion varied with the sulphur and organic matter intakes. Excretion of organic sulphur and total sulphate in urine and faeces increased with sulphur intake. The ratio of nitrogen to sulphur in faeces declined when sulphate was given. The retention of nitrogen was correlated with sulphur retention. It was concluded that the intake and digestion of the hays were not limited by the intake of sulphur.

Effect of stocking rate and fertilizer on the performance of steers grazing Townsville stylo-based pasture in north Queensland

The performance of steers grazing Townsville stylo (Stylosanthes humilis)-native grass pasture, with and without superphosphate fertilizer, was studied at two stocking rate (0.41 and 0.82 beasts ha-1) on the sub-coastal spear grass region of the dry tropics of north Queensland over a period of three and a half years. Fertilizer increased yield and quality of pasture, but invasion of the fertilized areas by annual grass species was occurring by the end of the study. Liveweight gains on fertilized Townsville stylo pastures were greater than on unfertilized Townsville stylo, where performance was similar to that recorded on untreated native pasture at stocking rates of 0.25 and 0.41 beasts ha-1. Liveweight gains at the lighter stocking rate were greater than at the higher level on the Townsville stylo-native grass pasture, but at the stocking rates applied to native pasture there was no significant effect of stocking rate. A stocking rate of 0.41 beast ha-1 on fertilized Townsville stylo was safe in all years. Wastage of material was high owing to mould development on the Townsville stylo which remained as standing hay during the winter.

Digestion of polysaccharide constituents of tropical pasture herbage in the bovine rumen : Part IV. The hydrolysis of hemicelluloses from spear grass by cell-free enzyme systems from rumen fluid

Hemicelluloses have been isolated from spear grass ( Heteropogon contortus), before and after digestion in the rumen, and separated into linear and branched fractions. Similar fractions have also been obtained from a pasture sample and from the faeces fibre of a steer fed on the same pasture. The rates of hydrolysis of all of these hemicellulose fractions have been determined in the presence of extracellular enzymes from rumen fluid and of enzymes liberated by disruption of rumen microorganisms. The oligosaccharide products of such enzymic degradations have been partially identified. The results confirm that the incomplete digestion of hemicelluloses in the rumen is due to physical protection ( e.g. by lignin), rather than to structural differences between different components of the hemicelluloses. There is no difference between rates of digestion of branched and linear hemicelluloses, and previous results which indicated such differences were probably caused by presence of a readily digested glucan in linear hemicellulose fractions.

Digestion of polysaccharide constituents of tropical pasture herbage in the bovine rumen : Part III. Examination of the celluloses and hemicelluloses of spear grass ( heteropogon contortus) which resist digestion

The hemicellulose and cellulose components of spear grass which survive digestion in cattle have been examined by isolation of these polysaccharide fractions from the following samples: ( i) fresh spear grass, ( ii) spear grass held in the rumen for 3 days, ( iii) a mixed pasture sample (predominantly spear grass), ( iv) faeces fibre from cattle fed on ( iii). The digested samples showed lower contents of cellulose and higher contents of hemicellulose than the undigested samples. The hemicellulose-B components from each were further separated into linear and branched fractions and compared. In all cases, the branched hemicellulose contained more arabinose and uronic acid than the corresponding linear hemicellulose. The arabinose content of the samples of undigested hemicellulose-B was higher than that in the digested samples.

Digestion of polysaccharide constituents of tropical pasture herbage in the bovine rumen Part II. Spear grass ( Heteropogon contortus)

The digestion of the polysaccharide constituents of spear grass ( Heteropogon contortus), namely hemicelluloses and cellulose, has been studied by enclosing samples in Terylene bags in the bovine rumen. Hemicelluloses (measured by total xylose content) and cellulose were digested slowly and incompletely (∼30% and ∼50%, respectively). The arabinose component of the hemicelluloses was digested slowly, but more extensively than the xylose component ( e.g., 45% and 30%, respectively). The resistance of these polysaccharides to complete digestion in the rumen appears to be due to physical protection by lignin.

The utilization of spear grass (Heteropogon contortus). III. The influence of the level of dietary sulphur on the utilization of spear grass by sheep

The effect of additions of sulphate to a spear grass diet fed to sheep with or without urea supplements was studied. With spear grass (0.39 g nitrogen/100 g dry matter), sulphate additions did not improve intake or digestion, but nitrogen retention was improved. With urea-supplemented spear grass, sulphate additions caused an increase in intake, digestion, and nitrogen retention. Nitrogen retention reached a plateau of about 2.5 g nitrogen per day. Sulphate added in excess of that required for microbial synthesis was excreted mainly as urinary sulphate. Nitrogen and sulphur in blood, rumen liquor, urine, and faeces were determined and the interrelationships between these variables are discussed. The differences between results of this experiment and results previously reported are discussed in relation to the variation in nitrogen content of mature spear grass between years, and to nutrition of the grazing ruminant.

The utilization of spear grass (Heteropogon contortus). I. Factors limiting intake and utilization by cattle and sheep

The addition of 13.6% lucerne to a diet of spear grass increased the total intake of digestible organic matter of cattle by nearly 30%. Further additions (24.5 and 44.9%) increased the total organic matter intake, but decreased the spear grass intake. In cattle, the digestibility of the spear grass portion of the diet appeared to decrease as lucerne was added to the diet. Sheep consumed and digested spear grass poorly, although an addition of 14.4% legume increased both digestibility and intake. Further additions of legume slightly decreased the digestibility of the spear grass. The addition of urea alone did not influence digestion or feed intake by either cattle or sheep. When cattle were fed on spear grass, urea, and minerals, the quantity of organic matter digested was not significantly different from that with a diet of spear grass and 20% lucerne. The digestibility of the spear grass was not influenced by urea and minerals, whereas it decreased with the addition of lucerne. Increased feed consumption was maintained when various components of the mineral supplement were withdrawn, excepting nitrogen and sulphur. The energy derived from diets of spear grass and lucerne or spear grass and minerals appears to be above the maintenance requirements of cattle, but below those of sheep.

Nutritional value of Townsville stylo (Stylosanthes humilis) and of spear grass (Heteropogon contortus)-dominant pastures fed to sheep. 1. The effect of plant maturity

The voluntary dry matter intake, digestibility and chemical composition of Townsville stylo and of black spear grass cut at different times of the year from a site near Townsville, Queensland, have been examined using penned sheep. Nitrogen, sulphur, and phosphorus intakes and retention in the sheep were measured. The concentrations of N, P, S, Na, and Ca in most cuts of spear grass and P and Na in Townsville stylo were less than the published requirements of animals. With spear grass, digestible dry matter intake declined rapidly from January to April and more slowly from April to October and by mid-March fell below the estimated energy requirements for maintenance of sheep. There was little change in digestible dry matter intake of Townsville stylo between February and May and the level was well above maintenance requirements. Dry matter intake and dry matter digestibility were linearly related but only about 50 per cent of variations in intake were caused by variations in digestibility. Nitrogen balance was linearly related to nitrogen intake, and sulphur balance was linearly related to sulphur intake. Phosphorus intakes were usually less than 1 g P day-l and animals were usually in negative P retention.

A comparison of the nutritional value of spear grass (Heteropogon contortus)-dominant pastures and Urochloa grass (Urochloa mosambicensis)

Both spear grass and Urochloa grass were cut at six intervals between January and October, near Townsville, Queensland, and the herbages, which ranged in age from 37-296 days, were fed to sheep indoors to compare voluntary dry matter intake, dry matter digestibility, and intake and retention of nitrogen, sulphur, and phosphorus. The dry matter intake and intake of digestible dry matter of Urochloa were greater than those of spear grass but dry matter digestibilities were similar at the same stage of growth. After mid-March, voluntary intake of digestible dry matter of both pasture species by the sheep was less than the amount needed to meet energy requirements. Nitrogen and phosphorus concentrations were higher in Urochloa than in spear grass, but the reverse applied to sulphur. Sheep were in negative nitrogen, sulphur, and phosphorus balance after early March, even though both grasses had been fertilized with superphosphate.

Effect of sulphate ion on the in vitro rumen digestion of polysaccharide constituents of bagasse.

The dry matter digestibility (DMD) of poor quality roughages such as spear grass (Heteropogon contortus) by sheep and cattle has been shown to increase on addition of sulphur to the diet. The sulphur is added most frequently as inorganic sulphate, either alone (Playne 1969) or supplemented with urea (Bray and Hemsley 1969; Kennedy and Siebert 1972; Siebert and Kennedy 1972) or gluten (Playne 1969). These supplements have also increased feed intake in sheep (Playne 1969; Kennedy and Siebert 1972; Siebert and Kennedy 1972) and cattle (Siebert and Kennedy 1972), and have improved the nitrogen and sulphur balance (Moir, Somers, and Bray 1967; Bray and Hemsley 1969; Playne 1969; Kennedy and Siebert 1972) within the animal. Sulphates have been shown to increase the in vitro rumen digestion of starch (Kennedy, Mitchell, and Little 1971), crude fibre (Bray and Hemsley 1969), and acid-detergent fibre and cellulose (Barton, Bull, and Hemken 1971).

Polysaccharides of tropical pasture herbage. VI. Identification of myo-inositol, galactinol, and raffinose in spear grass (Heteropogon contortus)

Polysaccharides of tropical pasture herbage. VI. Identification of myo-inositol, galactinol, and raffinose in spear grass (Heteropogon contortus)

The utilization of spear grass (Heteropogon contortus). II. The influence of sulphur on energy intake and rumen and blood parameters in cattle and sheep

Sheep and cattle were used to study the influence of nitrogen and sulphur on the consumption and digestion of spear grass. With sheep, additions of sulphur to the diet increased the digestibility and intake of the feed. The relatively high levels of plasma urea which were found in sheep fed on spear grass alone, decreased with sulphur intake. In cattle, sulphur supplementation did not increase the digestibility of feed. The levels of plasma urea were comparable with those of sheep receiving additional sulphur, which suggested that sufficient sulphur was returned to the bovine rumen to maintain digestion. As previously shown, feed intake was further raised in cattle receiving supplements of nitrogen and sulphur. With the addition of sulphur to the diet of spear grass and urea, the concentration of rumen ammonia was reduced and more nitrogen was retained. The levels of serum sulphate in groups of heifers fed in yards or at pasture demonstrated that sulphur may be limiting for the optimum utilization of spear grass in particular situations.

Nutritional value of Townsville stylo (Stylosanthes humilis) and of spear grass (Heteropogon contortus)-dominant pastures fed to sheep. 2. The effect of superphosphate fertilizer

Penned sheep were used to measure the voluntary dry matter intake, digestibility and chemical composition of Townsville stylo and of black spear grass fertilized at three different annual rates of superphosphate -0, 125 and 750 kg ha-1. Dry matter intake of spear grass fertilized at 125 kg ha-1 was greater (P<0.05) than that of spear grass fertilized at 750 kg ha-1, which in turn was greater than that of grass not fertilized (P<0.05). Dry matter digestibilities were generally similar, although the digestibility of the grass fertilized at 125 kg ha-l tended to be greatest. In Townsville stylo, no significant differences in intake or digestibility occurred with different fertilizer treatments.

Changes in soil nitrogen following different establishment procedures for Townsville stylo on a solodic soil in north-eastern Queensland

The effect of the legume Townsville stylo (Stylosanthes humilis) on soil nitrogen status was studied under mown plots with different conditions of establishment and fertilizer application on a solodic soil in north- east Queensland. Increase in soil total nitrogen 0-7.5 cm of 180 kg N per ha and total nitrogen accession (plant and soil) of 460 kg N per ha was measured over a four year period where the legume was sown into existing spear grass and fertilized with superphosphate at 375 kg per ha per year. Soil nitrogen increases did not occur until the pasture was legume dominant and main increases took place where superphosphate was applied. Under these conditions there was also a dry season accumulation of soil nitrate nitrogen.

Growth and water metabolism of cows and progeny on fertilized and unfertilized tropical pastures

Growth of Brahman x Shorthorn cows and their calves grazing unfertilized and fertilized pasture was studied in relation to body water content and water turnover; the main plant species in the pasture were spear grass (Heteropogon contortus) and Townsville stylo (Stylosanthes humilis). During the dry season, prior to the birth of calves, there was little difference in body weight or body composition between cows from the unfertilized and fertilized areas, despite the greater yield of pasture on the latter. The increase in body weight of both groups after the onset of the new season was due to expansion of the body water space. Body solids did not increase until c. 2 months later. The cattle from the fertilized pasture continued to increase in weight over the entire wet season at a significantly faster rate (P < 0.001) than those in the unfertilized pasture, and this latter group ceased growing a month before the end of the season. There was no significant difference in birth weight between the two groups of calves, although those from the fertilized pasture were significantly heavier at 2 weeks of age; during these 2 weeks they had received 45 % more milk, and until about 20 weeks they continued to grow more rapidly and turn over more water than the group from the unfertilized pasture. From 20 weeks the quality of the forage in the unfertilized pasture became superior, owing to the relatively high proportion of legume (Stylosanthes humilis), and the calves from the unfertilized pasture grew more rapidly until the end of the wet season. Plant nitrogen content was reflected in plasma urea nitrogen levels. The relationship between pasture quality and growth of cows and their calves is discussed.

Fertility and seasonal changes in liveweight of Droughtmaster cows grazing a Townsville stylo-spear grass pasture

An experiment was conducted to examine the fertility and seasonal changes in liveweight of cows grazing a Townsville stylo–spear grass pasture for over 4 years. There were two replicates of 12 treatments, which were factorial combinations of two stocking rates and three levels of superphosphate with and without conservation of hay. All experimental factors influenced cow liveweight. Cows on the pastures receiving superphosphate were heavier throughout the experiment than cows on unfertilized (F0) pasture; in most years there was little difference between pastures receiving superphosphate at 377 kg/ha (F3) and 126 kg/ha per year (F1). Stocking rate and conservation of hay had smaller but significant effects throughout the experiment. There were also marked seasonal fluctuations in cow liveweight associated with the amount and distribution of rainfall. Superphosphate was the only treatment that significantly affected conception and calving rate (F3 > F1, F0 at P < 0.01). Numerical analyses published elsewhere of average cow liveweight before and after mating and of conception rate strongly indicated a direct effect of superphosphate on conception rate that could not be explained by liveweight differences. This effect was primarily associated with the highest rate of superphosphate (F3), the F1 effect being more equivocal. There were significant differences between the three rates of superphosphate in the rate of change of cow liveweight during the first lactation (F3 > F1 > F0 at P < 0.05) but the differences appeared inadequate to influence conception rate markedly. Without fodder conservation, 1 cow unit to 2.4 ha was a safe stocking rate for fertilized pastures. This is three to four times the carrying capacity of unimproved spear grass pastures in the region.

Polysaccharides of tropical pasture herbage. I. Studies on the distribution of the major polysaccharide components of spear grass (Heteropogon contortus) during growth

The total carbohydrate content of spear grass stalk and leaf at several different stages of growth has been separated into fractions by a sequence of extraction procedures and each major polysaccharide fraction has been analysed for its monomer composition. As growth advanced the low molecular weight carbohydrates (sucrose, glucose, fructose) decreased, while hemicelluloses and cellulose increased in relative amount. Hemicelluloses, which are the major type of component in the plant, were predominantly of the B-type in the leaf, but both A- and B-types were present in the stem. The hemicellulose A-fractions contained proportionately less arabinose and uronic acid and more xylose than the corresponding B-fractions.