Preservation of plant material by large scale sorption freeze-drying

A large-scale sealed system for freeze-drying herbage is described. It utilizes the principle of sorption drying and is dependent upon the vapour pressure differential (VPD) between the herbage and the silica gel drying agent. Ice sublimes to vapour from the sample in a system operating at approximately – 10°C and the vapour is adsorbed by silica gel in an air stream recycled by a blower; equal masses (up to 50 kg each) of wet herbage and silica gel are used. The system is simple to construct and is relatively inexpensive.
Approximately eight days drying time are needed to reduce moisture content from 90 to 10%. Twenty-four different species or cultivars of both temperate and tropical grasses and legumes sampled at several stages of maturity have been dried in the system. When snap-frozen herbage is freeze-dried by this process the physical and chemical changes that otherwise occur when herbage is harvested and prepared for evaluation can be reduced and sufficient material can be obtained to permit animal feeding studies as well as chemical analyses.     

MICROWAVE DRYING OF HERBAGE

Microwave heating has recently been suggested as a method of drying herbage. A slightly modified commercial microwave cooking-oven has been tested for this purpose and was found to dry 400 g of fresh herbage in 15-20 min. The water-soluble-carbohydrate contents of herbage samples dried ( a ) by microwaves and ( b ) by freezing were similar.     

THE VISUAL ESTIMATION OF PASTURE AVAILABILITY USING STANDARD PASTURE CORES

A coring technique (6), that may be used for estimating the mean amount of herbage on closely grazed pastures, has been adapted to include visual scoring. Two methods are described, both of which use sets of pasture cores from the sward as reference standards. The observers score the herbage on view at random sites against the standards. In the first method the scores are converted to herbage yields directly by reference to the yields of the standards. In the second method a double sampling regression technique is used and the set of standards is used as a visual guide only.     

Effect of nitrogen fertilization on herbage production of tall fescue swards continuously grazed by sheep. 2. Consumption and efficiency of herbage utilization

The effect of a reduced level of nitrogen fertilizer application upon the herbage consumption of a continuously grazed sward of tall fescue has been investigated during two successive years. Two contrasting cultivars were used and two levels of leaf area index were maintained on the swards in order to obtain a wide range of sward structure. The herbage growth, herbage senescence and herbage consumption were measured directly on labelled tillers. It was possible to estimate the different components of the defoliation process (frequency and intensity) at the level of individual tillers of each leaf category. The results show that the effect of reduction in N fertilizer on herbage consumption rate is proportionally more important than that on herbage growth rate. In consequence, the efficiency of herbage utilization in continuously grazed conditions is reduced when nitrogen nutrition becomes limiting for herbage growth. The data suggest that this phenomenon is not directly attributable to nitrogen deficiency but is an indirect effect owing to the reduction of the stocking density at the low N level, which leads to a lower frequency of defoliation of individual tillers.     

Interactions between leaf lifespan and defoliation frequency in temperate and tropical pastures: a review

In continuously stocked swards or pastures the frequency at which individual tillers and individual leaves are defoliated by ruminant livestock, relative to leaf lifespan of the grass species within the sward, determines the proportion of each leaf defoliated before senescence, and hence the efficiency of harvesting of herbage. In this paper, sets of data obtained in a range of climatic conditions and with a range of grass species are used in order to document this relationship. It is shown that the frequency of defoliation of individual tillers or individual leaves is closely linked to the average stocking density used within a period of time for maintaining a steady state sward or pasture height, herbage mass or leaf area index. Consequently, any decrease in herbage growth rate should lead to a decrease in the efficiency of harvesting of herbage and then to a more than proportional decrease in total herbage consumption by ruminant livestock. These effects will be more important for grass species having short leaf lifespan than for species with long lifespan. In rotational stocking, the link between herbage growth rate and frequency of defoliation of leaves can be broken by controlling the grazing interval, so any decrease in herbage growth would not be systematically associated with a decrease in efficiency of harvesting of herbage. Rotational stocking should be more efficient than continuous stocking in low herbage production conditions, while in high herbage production systems rotational and continuous stocking would have similar efficiency. The implications of these conclusions for the management of swards and pastures to meet different objectives are discussed briefly.     

The use of conserved forage as a supplement for grazing dairy cows

The difficulty in matching the herbage requirements of grazing dairy cows to herbage production, due mainly to the unpredictability of the latter., causes stocking rates to be too low for maximum per hectare production and, thus, cows to be underfed at certain times in the grazing season. Conserved forage may be used as a supplement for grazing dairy cows in order to reduce variation in forage intake by the cow, to allow pasture stocking rates to be increased and to increase the efficiency of land use. The effect of offering conserved forage with herbage on intakes and production is reviewed in comparison to both ad libitum and restricted herbage. Total nutrient intakes and milk fat + protein yields are reduced for cows offered herbage and supplementary forage compared with cows offered ad libitum herbage, but increased compared with cows offered a restricted herbage level. Increasing pasture stocking rates may allow increases in utilized metabolizable energy levels from grassland but further research is needed in this area. Both grass and maize silage supplements offer potential for increasing the efficiency of land use, but in the case of grass silage this is only achieved in the best management practices.     

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.     

STUDIES IN HERBAGE DIGESTIBILITY

White-clover herbage proved to be of relatively high digestibility and it was possible to predict the digestibility of mixed grass and clover herbages from a knowledge of the digestibility and proportions of the components. Lucerne proved to be of low digestibility. Aftermath herbage was not so highly digestible as first cuts; and in autumn digestibility falls slowly as herbage ages. Digestibility was unrelated to the nitrogen content of herbage. In three trials no significant differences were found between the digestive efficiencies of wether sheep and dairy cows, while hormone implantation, although affecting animal metabolism, failed to influence feed digestibility. Restricted feeding at 50% of the ad libitum intake resulted in a slight increase in the apparent digestibility of herbage.     

SOME ESTIMATES OF THE AREAS OF PASTURE FOULED BY THE EXCRETA OF DAIRY COWS

Observations were made of the areas of herbage receiving the faeces of grazing dairy cattle and of the areas and relative palatability of herbage whose growth was affected by faeces and urine. The average area covered by faeces was 7·3 sq. ft./cow/day. Faeces dropped during grazing had a negligible affect on the utilization of herbage at that grazing, but each dung-pat probably affected the growth and palatability of an area of herbage about six times as great at the next grazing. The area of herbage whose growth was affected by urine was equal to that affected by faeces, but unlike faeces, urine improved the palatability of the herbage to dairy cows. The data were used to calculate approximate areas of herbage likely to be affected by excreta at different levels of stocking, and it appeared that excreta return plant nutrients to a given pasture acreage more quickly than some other estimates suggest.     

The reaction of grazing sheep and cattle to the presence of dung from the same or the other species

An experiment is described in which steers and wether sheep separately grazed perennial ryegrass swards, managed so that half of each sward had previously been grazed by sheep and half by cattle. The influence of the presence of dung from the same or the other species on grazing patterns and herbage utilization was examined.
Regression analysis of extended sward height along transects laid across dung pats after grazing revealed that the limits of the rejected herbage were more clearly defined around cattle dung than sheep dung when grazed by cattle, whereas there was less distinct avoidance of herbage around both cattle and sheep dung when grazed by sheep. As grazing proceeded there was a progressive movement of animals from the half of the plot previously grazed by the same species to the half previously grazed by the opposite species, and this movement was more marked in the cattle than in the sheep.
It was concluded that under mixed grazing a greater proportion of the herbage would be available to the sheep giving them an advantage over the cattle.     

THE NORMAL-ACID FIBRE CONTENT OF SPFCIES AND VARIETIES OF HERBAGE GRASSES

Normal-acid fibre content has been suggested as a useful indication of the digestibility of herbage. The changes in fibre content were therefore recorded during the spring and early summer of 1957 and 1958 to see whether regular differences occurred between species and varieties of herbage grasses.
All species showed an increase in fibre content during spring and early summer, but considerable year-to-year fluctuations occurred: fibre content was also influenced by manuring and spacing. Regular differences between species and varieties have been detecled and, in perennial ryegrass, differences between individual genotypes. It should be possible to select breeding material for high or low fibre content if required.     

Changes in the herbage nutritive value and yield associated with threshold responses of vegetation to grazing in Mongolian rangelands

We examined the changes in the nutritive value and yield of herbage along a grazing gradient, where abrupt changes in community composition occurred, at multiple ecological sites in Mongolian rangelands. At grassland sites, changes in the herbage nutritive value could be attributed to rapid replacement of perennial grasses or forbs with weedy annual forbs along a grazing gradient. Crude protein (CP) concentration increased sharply in approaching the source of grazing gradient, whereas neutral detergent fibre and metabolizable energy (ME) concentrations decreased sharply. As ME can be utilized as a main index of herbage nutritive value, these results indicated its overall loss with severe grazing. Consequently, gradual increases in the yields of CP and ME in the direction of the gradient source at the grassland sites did not necessarily indicate the improvement of rangeland condition. In contrast, at shrubland sites, we could not generally detect any significant trends in the herbage nutritive value. The yield of ME gradually decreased in the direction of gradient source, suggesting that grazing affects herbage yield rather than herbage feed value at shrubland sites. Thus, the nutritive value and yield of herbage can be modified greatly in association with nonlinear responses of vegetation to livestock grazing.     

THE ESTIMATION OF 'GREEN DRY MATTER' IN A HERBAGE SAMPLE BY METHANOL-SOLUBLE PIGMENTS

To estimate the proportion of the total dry matter of a herbage sample which arises either from dead or from green herbage, four methods have been compared. One of the methods, the pigmentation method, is described.     

The effect of herbage surface water and the provision of supplementary forage on the intake and feeding behaviour of cattle

High rainfall and the corresponding low herbage DM content has been shown to adversely affect cattle intakes and production. This could arise from physical restrictions on intake or digestion rate, or other behavioural limitations such as reduced palatability. A knowledge of the reason for the intake reduction would assist in determining the optimum supplement to feed. Eight steers were offered four diets in a changeover design. The diets were: A, cut herbage; B, cut herbage with added surface water; C, as B but with a low dry matter (DM) forage supplement (silage); and D, as B but with a high DM forage supplement (hay). The addition of surface water to herbage reduced DM intake and feeding time but had no effect on biting rate or rate of intake. Neither hay nor silage was eaten in sufficient quantities to restore DM intake, even though the silage was of similar nutrient composition to the herbage.     

The effects of variation in sward characteristics upon the ingestive behaviour and herbage intake of calves and lambs under a continuous stocking management

Groups of calves and lambs grazed on plots of S23 perennial ryegrass, in successive periods of 2, 2 and 3 weeks, at stocking rates which resulted in a slow change in herbage mass on each plot and measurements were made of ingestive behaviour (biting rate, bite size and grazing time) and herbage intake. As the green herbage mass was progressively reduced from approx. 3000 to 1000 kg OM per ha between periods, biting rate and grazing time increased, but insufficiently to offset the rapid fall in bite size so that herbage intake declined by 24% and 39% for calves and lambs respectively. Patterns of response were similar in calves and lambs, though in all parameters except biting rate the lambs appeared to be more sensitive than the calves to changes in sward conditions and there was no evidence that lambs were better adapted to grazing on short swards than calves. Intake increased in both calves and lambs up to levels of 2500–3000 kg green OM per ha, though this response may have been attributable in part to the reinforcing effects of increasing herbage mass and diet digestibility. Lambs consistently selected a more digestible diet than calves. Both calves and lambs increased grazing time substantially in response to limiting sward conditions, in contrast to results in earlier strip-grazing trials with calves, thus supporting the suggestion that the lack of response under strip-grazing is a characteristic of the management imposed.     

Sodium fertilizer application to pasture. 9. The effects of combined or separate applications of sodium and sulphur fertilizers on herbage composition and dairy cow production

An experiment was conducted to examine the response of herbage grazed by dairy cows to sodium fertilizer applied with or without sulphur fertilizer. The residual effects of applying sodium fertilizer in the previous year were also evaluated. The application of sodium or sulphur fertilizer did not affect herbage growth or height, but the application of sulphur fertilizer increased crude protein content of herbage. The increase in sodium content with application of sodium fertilizer was small, but was greater when sodium fertilizer had also been applied in the previous year. Herbage potassium was increased when sodium fertilizer was applied in the year of the experiment, but only if sodium had not been applied in the previous year. Application of sulphur fertilizer increased herbage sulphur content and reduced the contents of boron, chromium, molybdenum and nickel. Cows grazing pasture that had received sodium fertilizer had increased milk yields and the content of lactose in milk, whereas those grazing pasture that had received sulphur fertilizer application had reduced milk yields and the content of milk fat.     

THE EFFECT OF ENSILING ON CROP DIGESTIBILITY

The digestibilities of 22 herbages, and of the silages made from them, were measured with sheep: in two experiments batches of the same herbage were ensiled by several different methods. In every case the digestibilities of herbage and of the corresponding silages were found to be very similar, and no significant effect of method of ensilage on digestibility was found. The importance of using the true dry-matter content of silages (i.e. corrected for losses of volatile constituents during drying) is emphasized; a depression in the digestibility of herbage during ensilage is likely to be estimated unless this correction is made. These experiments have shown that silage of high digestibility (>80%) can be made from highly digestible herbage; however the intakes, both of dry matter and of digestible dry matter, from such silages were found to be much lower than expected. If the potential for animal production of high digestibility in silage is to be exploited, intakes must be in-creased; two possible measures, viz. the wilting of herbage before ensilage, and the use of high-digestibility forages of high soluble carbohydrate contents, are discussed.     

Modelling the concentrations of nitrogen and water-soluble carbohydrates in grass herbage ingested by cattle under strip-grazing management

There is scope of increasing the nitrogen (N) efficiency of grazing cattle through manipulation of the energy and N concentrations in the herbage ingested. Because of asymmetric grazing by cattle between individual plant parts, it has not yet been established how this translates into the concentrations of N and water‐soluble carbohydrates (WSC) in the herbage ingested. A model is described with the objective of assessing the efficacy of individual tools in grassland management in manipulating the WSC and N concentrations of the herbage ingested by cattle under strip‐grazing management throughout the growing season. The model was calibrated and independently evaluated for early (April), mid‐ (June, regrowth phase) and late (September) parts of the growing season. There was a high correlation between predicted and observed WSC concentrations in the ingested herbage (R² = 0·78, P < 0·001). The correlation between predicted and observed neutral‐detergent fibre (NDF) concentrations in the ingested herbage was lower (R² = 0·49, P < 0·05) with a small absolute bias. Differences in the N concentration between laminae and sheaths, and between clean patches and fouled patches, were adequately simulated and it was concluded that the model could be used to assess the efficacy of grassland management tools for manipulating the WSC and N concentrations in the ingested herbage. Model application showed that reduced rates of application of N fertilizer and longer rotation lengths were effective tools for manipulating herbage quality in early and mid‐season. During the later part of the growing season, the large proportion of area affected by dung and urine reduced the effect of application rate of N fertilizer on herbage quality. In contrast, relative differences between high‐sugar and low‐sugar cultivars of perennial ryegrass were largest during this period. This suggests that high‐sugar cultivars may be an important tool in increasing N efficiency by cattle when risks of N losses to water bodies are largest. The model output showed that defoliation height affects the chemical composition of the ingested herbage of both the current and the subsequent grazing period.     

Response of herbage regrowth and water-soluble carbohydrate concentration of ryegrass species to defoliation practices when grown in a Mediterranean environment

Three experiments were conducted to determine the association between leaf number per tiller at defoliation, water‐soluble carbohydrate (WSC) concentration and herbage mass of juvenile ryegrass plants when grown in a Mediterranean environment. Seedlings of ryegrass were grown in nursery pots arranged side‐by‐side and located outside in the open‐air to simulate a mini‐sward in Experiments 1 and 2, and a mixture of annual ryegrass and subterranean clover (Trifolium subterraneum L.) was grown in a small plot field study in Experiment 3. Swards were defoliated mechanically with the onset of defoliation commencing within 28 d of germination. Frequency of defoliation ranged from one to nine leaves per tiller, whilst defoliation height ranged from 30 mm of pseudostem height that removed all leaf laminae in Experiment 1, to 50 mm of pseudostem height with some leaf laminae remaining post‐defoliation in Experiments 2 and 3. A positive relationship between herbage mass of ryegrass, WSC concentration and leaf number per tiller at defoliation was demonstrated in all experiments. In Experiment 1, the herbage mass of leaf, pseudostem and roots of tillers defoliated at one leaf per tiller was reduced to 0·10, 0·09 and 0·06 of those tillers defoliated less frequently at six leaves per tiller. However, the reduction in herbage mass from frequent defoliation was less severe in Experiment 2 and coincided with a 0·20 reduction in WSC concentration of pseudostem compared with 0·80 measured during Experiment 1. In Experiment 3, the highest harvested herbage mass of ryegrass occurred when defoliation was nine leaves per tiller. Although the harvested herbage from this sward contained senescent herbage, the in vitro dry‐matter digestibility of the harvested herbage did not differ significantly compared with the remaining treatments that had been defoliated more frequently. Leaf numbers of newly germinated ryegrass tillers in a Mediterranean environment were positively associated with WSC concentration of pseudostem and herbage mass. A minimum period of two to three leaf appearances was required to restore WSC concentrations to levels measured prior to defoliation thereby avoiding a significant reduction in herbage mass. However, maximum herbage mass of a mixed sward containing ryegrass and subterranean clover was achieved when defoliation was delayed to nine leaves per tiller.