Agriculture group symposium recent developments in forage conservation and feeding

J . Sci. Food Agric. 1987,39,221-231

Agriculture Group Symposium Recent Developments in Forage Conservation and

Feeding

The following are summaries of papers presented at a meeting of the Agriculture Group of the Society of Chemical Industry held on 18 November 1986 at the Society of Chemical Industry, 14-15 Belgrave Square, London SWlX 8PS. The papers published here are entirely the responsibility of the authors and do not reflect the views of the Editorial Board of the Journal of the Science of Food and Agriculture.

Grass Silage in UK Agriculture

A. R. Henderson

The Edinburgh School of Agriculture, West Mains Road, Edinburgh EH9 3JG, UK

The 1985 Agricultural Census shows that the area of grasses cut for silage continues to increase whereas the area cut for hay and artificial drying has decreased gradually in recent years. This changeover from mainly hay to silage as conserved fodder has resulted from the introduction of the forage-harvester and from a better understanding of the biochemistry of the ensilage process. Chop- ping the grass into short lengths improves compaction in the silo and releases substrate for the indigenous lactic acid bacteria. With the wide range of silage additives available to the farmer, the fermentation process need no longer be left to chance.’

The increase in the capacity of silage-making tackle and the commensurate increase in the cost of silage production has led research workers to consider less sophisticated harvesting systems. One low-cost system uses the big baler. Initially developed for the small-scale livestock producer who wanted to switch from hay to silage, it has now been adopted on larger units. Even with a good fermentation, baled silage has a lower intake potential than short-chop clamp silage made from similar grass. Direct flail cutting gives a shorter chop length than the big bale, uses less power than the pre-wilt precision-chop system and can be more efficient than either of these.2

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J . Sci. Food Agric. (39) (1987)-@ Society of Chemical Industry, 1987. Printed in Great Britain

222 Developments in forage conservation and feeding

The results of Eurowilt3 demonstrate that direct-cut silage treated with an effective additive will be as good as, if not better than, wilted silage made from similar grass. Adopting the direct-cut system brings the farmer into conflict with the conservationist. Effluent, one of the strongest pollutants to enter water- courses, must be collected in tanks and can be fed to stock4 or diluted and sprayed on the land. Many silage additives contain acids or acids with formalin, but manufacturers and research workers are now seeking to replace these with biological additives which are both safe to handle and effective in use.

The quantity of silage made in the UK is increasing but the number of cows is decreasing. At the Dairy Farming Event at Stoneleigh, milk producers were urged not to cut back on feeding. Scots dairy farmers who were below target on milk quota for the year ending in April 1987 were encouraged to maximise silage intake. Failure to maintain production during this autumn and winter could put Scotland below quota next April.

With cattle numbers down, more silage is being fed to sheep, both stored lambs and housed ewes. Hay is the traditional winter food for sheep, but good quality silage of high digestibility can be fed to ewes as their sole food up to two weeks before parturition.

Grass is the commodity which British farmers grow best, but our grassland is not always used to its full potential. Manipulation of fertiliser application and a buffer feeding system can maximise grass production. Efficient silage making and judicious supplementation of silage will ensure maximum animal production.

References

1. Wilkinson, J. M. Silage UK. Chalcombe Publications, Marlow, Bucks, UK, 1986. 2. Gordon, F. J. The effect of systems of silage harvesting and feeding on milk production.

3. Zimmer, E.; Wilkins, R. J. Efficiencyof silage systems: acomparison between unwilted

4. Steen, R. W. J. An evaluation of effluent from grass silage as a feed for beef cattle

Grass and Forage Sci. 1986, 41, 209-219.

and wilted silages. Landbauforschung Volkenrode, 1984, 69.

offered silage-based diets. Grass and Forage Sci. 1986,41, 39-45.

Complementary Forage Crops for Milk Production

R. H. Phipps

The Animal and Grassland Research Institute, Church Lane, Shinfield, Reading RG2 9AQ, UK

The 7 million ha of effective grassland is the most important source of forage for grazing and conservation. In winter milk-production systems, conserved forage generally accounted for less than 50% of metabolisable energy (ME) intake. This occurred because of a relatively favourable milk to concentrate price ratio, and the ease with which concentrates could be acquired to mask inadequacies in existing stocks of grass silage.

Agriculture Group Symposium 223

With the arrival of milk quotas, many producers reduced production costs by decreasing concentrate input and attempted to place more reliance on forage. In this respect the potential advantages of high-quality grass silage have been clearly demonstrated but so have the drawbacks of lower dry matter (DM) yields ha-’ and the requirement for an increased conservation area if adequate winter forage is to be produced.

It is in the context of this inverse relationship between yield and quality of grass silage that the role of complementary forage crops should be considered. In order for such crops to be attractive to livestock producers they must offer some positive benefit. This may take the form of higher DM yields, better quality in terms of energy, protein or mineral concentration, improved consistency, lower production costs, a potential cash crop or allowing the production of high-quality grass silage by acting as a ‘silage replacer’ or ‘silage extender’.

The two main complementary forage crops providing a high energy concentration and a markedly more consistent product than grass silage are fodder beet and maize silage. The area of fodder beet has increased from 5000 ha in 1983 to 11500 ha in 1986, although no increase occurred in 1986. It is generally accepted that fodder beet has the potential to produce the highest yield of DM and ME of any forage crop including perennial ryegrass, and has the added advantage of also being an easily saleable commodity. However, although highly palatable and with the ability to increase forage intake, its complex growing requirements coupled with harvesting problems in November/December may be some of the reasons why the area under cultivation remained static during the 1986 growing season. In contrast the area of maize increased from 15000 ha in 1983 to 22000 ha in 1986, with a 20% increase occurring in 1986. Although used by some growers as an alternative to grass, its main use should be in conjunction with grass silage. Work at the Animal and Grassland Research Institute has shown that, with both average (60D) and high quality (67D) grass silage, access to maize silage will not only increase forage DM intake but will also improve quality and increase yield of milk constituents, and can reduce concentrate inputs.

At present, the area of forage legumes grown specifically for conservation is small. This is in spite of the fact that crops such as lucerne and red and white clover can increase DM intake by over 20% while providing 30% more non-ammonia nitrogen to the duodenum of dairy cows, and have produced highly significant increases in both milk yield and yield of milk constituents.

The spectre of nitrogen quota makes it important to consider the role of nitrogen in silage production. With grass silage, inorganic N fertiliser accounts for approximately 60% of total support energy inputs. Due to the high energetic costs of production for N fertiliser (80 MJ kg-1 N) the resultant energy input/output ratio is about 0.6. This does not compare favourably with ratios of 0.4 and 0.2 for legume and maize silages. These improved ratios are due to lower fertiliser requirements and the ability to utilise organic manures.

The use of untreated and treated (4% NaOH) barley straw fed in conjunction with high-quality grass silage is currently being evaluated as a silage replacer at the Bernard Weitz Centre, Shinfield, Reading. Preliminary results indicate that from mid-lactation 20% of high-quality grass silage can be replaced by treated straw


without affecting milk production. The use of untreated straw at the same inclusion rate led to decreased performance.

There is evidence to suggest that a range of complementary forage crops, which offer specific advantages within various management systems, should now be seriously considered by a large number of livestock producers.

New Developments in Forage Evaluation

J . K. Thompson and I. Murray

School of Agriculture, 581 King Street, Aberdeen AB9 lUD, UK

Forage crops vary in nitrogen, energy and mineral nutrient status more than most other feeds so that there is a continual need to analyse forages for research and farmer advice. Advances in research place an increasing burden on routine testing which has to be rapid, reliable and cost effective in predicting animal productivity. The animal integrates all the chemical and physical characteristics which together determine palatability, intake, digestibility and utilisation of nutrients. Prediction of animal performance needs an integrated multivariate solution based on data from carefully conducted animal trials such as those from the Feed Evaluation Unit, Rowett Research Institute, Aberdeen. We see a number of major developments altering the conventional approach to forage evaluation which include the following.

Improvements in the prediction of animal performance from modelling studies Modelling will increase our understanding of animal physiology and the animal’s response to nutrients. Components of the complex models of today will be incorporated into simpler schemes which can be applied in practical farming situations. This will lead in our opinion to better estimates of intake and improved sensitivity to ration changes and adjustments.

A displacement of the use of rumen fluid in in vitro systems of determining the digestibility of forages Animal welfare considerations will limit the use of animals in such studies. Fortunately, fungal enzymes with a broad spectrum of fibre-hydrolysing activity are now become available, and methods are already well advanced to displace the classical Tilly and Terry method.

The change from traditional analytical procedures to physico-chemical methods for the estimation of various forage attributes The most promising and most successful innovation is the application of near infrared (NIR) reflectance to forage analyses. We are assured that already the


prediction of digestible organic matter in the dry matter (DOMD) and crude protein in grass, hay and silage crops is sufficiently accurate for the needs of practical farmers. If it is desired, NIR methods are capable of further development and further refinement. The approach can be used, for example, to estimate the ratio of grass to legume in a mixed forage, and shows promise in the estimation of voluntary intake.

A comparison of NIR with alternative methods for silage analyses is illustrated in Table 1.

TABLE 1 Correlation of ‘D’ Estimated by Different Methods with in

vivo Values for 28 Silages

R2 SE

Lignin D 0.89 2.25 Modified acid detergent fibre D 0.51 4.68 In vitro D 0.69 3.71 Near infra-red reflectance D 0.85 2.61

Other physico-chemical approaches such as nuclear magnetic resonance (NMR) have not yet been developed to a stage at which they can be usefully applied to forages.

ICP-AES Inductively coupled plasma-atomic emission spectroscopy (ICP-AES) provides a rapid and relatively inexpensive method of analysing forages for mineral elements. A group of macro- and micro-elements can be determined in the same sample.

Areas needing development In some areas of interest progress has been disappointingly slow or is still dependent on cumbersome procedures. These include the methods used to describe heat or storage damage and to describe protein degradability, and the direct determination of water in fermented forages.

Recent Developments in Silage Additives

J. A. Rooke and D. G. Armstrong

Department of Agricultural Biochemistry & Nutrition, University of Newcastle upon Tyne, Newcastle upon Tyne NE17RU, England

Silage is now the major form in which grass is conserved for winter feeding to ruminant livestock in the UK. Conservation techniques have improved dra-


matically over the last 25 years, with the use of silage additives being a major contributor to this improvement. Silage additives can be considered to have several distinct functions in the ensilage process:

(1) To minimise the risk of an unsuccessful fermentation in adverse conditions. (2) To improve the efficiency of an otherwise successful natural fermentation. (3) To improve aerobic stability when the silage is fed.

The first is by far the most important in the UK situation. The variety of additives available on the UK market has widened considerably

in recent years with the advent or re-emergence of sulphuric acid, inoculants and enzymes. It is the mode of action and efficacy of these additives which will be discussed.

Sulphuric acid is a lower-cost alternative to formic acid as a means of reducing herbage pH rapidly at ensiling to ensure domination of the fermentation by lactic acid bacteria and thus to achieve a stable silage in conditions where substrate availability would otherwise limit the fermentation. However, unlike formic acid, sulphuric acid has no antimicrobial properties perse, and if applied in inadequate quantities a sulphuric acid based fermentation will carry a greater risk of an undesirable secondary fermentation than will a formic acid fermentation. Both these acid additives have little or no inhibitory activity against yeasts, which can survive low pH. Thus there is increasing awareness of the risk of yeasts fermenting sugars to ethanol with the consequent loss of crop dry matter in otherwise well ensiled material.

Although the criteria for selecting a lactic acid bacterium for use as a silage inoculant were first established 25 years ago, there is still considerable uncertainty over the efficacy of such products. Recent European collaborative research (EUROBAC, 1986) has summed up current knowledge.

(1) Most available inoculants are either ineffective or not as effective as formic

(2) Consistent improvements with inoculants are only obtained with wilted grass. (3) In part, the reason for the lack of success with inoculants may be related to the

numbers of lactic acid bacteria found naturally on crops at ensiling. The EUROBAC research has shown there to be lo4 to lo5 lactic acid bacteria g-l crop ensiled and not lo2 to lo3 as previously accepted.

(4) Therefore an inoculation rate of lo6 lactic acid bacteria g-l crop ensiled is needed to have a realistic chance of dominating the silage fermentation.

The most recent silage additives to appear have been the enzyme-based products. These products aim to make available to the silage microflora, substrates derived from the plant cell wall, and therefore to ensure that there is sufficient substrate available for a successful fermentation. In addition, continuing enzyme activity after completion of the silage fermentation may provide a different mix of substrates for the host animal when the silage is fed, and thus improve the nutritive value of the silage. However, there is little evidence to date about the efficacy of these additives.

acid when applied to wet, low-sugar crops.


Nutritional Aspects of Conserved Forages

P. C. Thomas

The Hannah Research Institute, Ayr KA6 5HL, UK

Forages can be conserved by artificial drying (dried grass), field drying (hay) and ensilage. The nutritional value of the feeds depends on the chemical composition of the initial crop (which is influenced by type, variety, growing conditions and stage of growth at harvesting) and by the conservation method. Artificial drying is now generally uneconomic except for specialist uses, and for ease of field drying, crops must be relatively mature and stemmy. Thus for immature crops of high nutritive value ensilage is the conservation method of choice. However, ensilage produces major changes in crop composition which vary with the ensilage method and its effectiveness. Typically the fermentation leads to hydrolysis of proteins, loss of water-soluble carbohydrates and formation of fermentation end-products (lactic acid, acetic acid, ethanol, etc). Adverse clostridial fermentations also lead to the production of ammonia, various amines and butyric acid. The effects of silage fermentation are quite crucial since they have a modulating influence on the underlying relationships between the digestible nutrient content of the crop and its feeding value.

The voluntary intake of silage dry matter (DM) has been reported to be less than for corresponding crops in dried form. However, the difference tends to be overestimated because of failure to account for silage volatiles in DM determina- tions. There is no clear understanding of the factors controlling silage intake. Rumen-fill mechanisms and chemostatic mechanisms depending on silage fermentation products have both been demonstrated. Intake is influenced by the amount and type of supplementary feed, and high-protein supplements are more effective than low-protein supplements in promoting silage consumption.

There are relatively few calorimetric data on the efficiency of utilisation of metabolisable energy (ME) for tissue synthesis and milk production in animals given diets containing a high proportion of silage. However, the data available indicate that for some silages the efficiency of utilisation is lower than predicted by the ME system. The presence of flavonoid compounds in silage has been suggested as a cause for the low efficiency but that has yet to be confirmed. Silage diets are extensively fermented in the rumen, and the ‘high-acetate’ fermentation which results is stable and relatively resistant to change. Starchy supplements which lead to ‘high-propionate’ fermentations and reduced milk-fat contents with dried forage diets thus generally have less impact with silage diets.

Silages are characterised by a high rumen degradability of nitrogen and a low efficiency of utilisation of nitrogen for rumen microbial protein synthesis. The latter is partly explained by the poor ATP yield derived from rumen fermentation of silage fermentation products. However, recent research suggests that microbial protein synthesis may be enhanced by using dietary supplements containing readily fermented sugars, proteins and sodium bicarbonate.


With many silage diets the passage of amino acids to the duodenum apparently fails to meet the animals' requirements, and there are particular limitations on the supply of methionine and lysine. Dietary supplements of low-degradability fishmeal designed to correct the animal's amino acid supply have increased milk yield by 8-20% in dairy cows. Similar responses have also been obtained with barley supplements formaldehyde treated to reduce their rumen degradability , but not as yet with 'rumen-protected' supplements containing methionine and lysine.

Feeding Value of Conserved Forages

C. Thomas" and R. Raeb

UAnimal and Grassland Research Institute, Hurley, Maidenhead SL6 SLR, UK and bICI Jealott's Hill Research Station, Bracknell RG12 6EY, UK

Grass silage is a major source of forage for the feeding of beef cattle and dairy cows during the winter. The objective of the paper is to examine the factors influencing animal performance from silage-based diets and in particular to discuss recent developments in the supplementation of silage.

Digestibility of the crop at cutting is clearly one of the most important factors influencing the performance of cattle given dried forage. Although voluntary intake and liveweight gains of beef cattle given ensiled herbage also tend to increase with increasing digestibility, the response is considerably modified by the fermentation characteristics of the silage. Nevertheless, high rates of liveweight gain (0.8 to 1.0 kg day-') can be achieved by beef cattle given silage of high quality as the sole feed, but there remain considerable disadvantages both in terms of a reduced efficiency of energy utilisation and a tendency to deposit a high proportion of fat in the empty body. When dairy cows have been given silage as the sole feed, voluntary intake has ranged between 11.5 and 13-6 kg DM day-' and milk yield between 19.3 and 23.1 kg day-I. However, these levels have been achieved at the expense of some loss in body weight and possibly growth, and the long-term consequences of this have yet to be established.

In view of the disadvantages of feeding silage as the sole feed much research effort has been expended on supplementation, but in the main cereal-based concentrates have been used. Results show high rates of substitution between the concentrate and high-quality silage, and thus the benefits from making high- digestibility silage with good fermentation characteristics are much reduced. Therefore, recent work has concentrated on the use of alternative supplements. For example, it has been shown that the inclusion of by-products containing fibre of high digestibility can elicit higher intakes of silage by dairy cows even at relatively low levels of feeding. Also the low supply of amino acids from silages has prompted work on protein supplements. The use of fishmeal has resulted in


increments in gain by beef cattle of between +Ow24 to +0-46 kg day-', the degree of response depending on the quality of the silage and the potential of the animal for the growth of lean tissue. Similar approaches have been taken with dairy cows, where equivalent milk yields have been observed with 1.3 kg DM of a fishmeal/soyabean meal mix as with 4.3 kg DM of commercial compound. Lacta- tion yields were 5200 kg with total supplement inputs of 0.21 and 0.70 t DM cow-' respectively. In other complete lactation trials where cows were given 0.25 t DM of high-protein supplements as the sole supplement to silage, lactation yields have ranged from 4950 to 5910 kg depending on the length of the winter feeding period and the quality of the silage. However, the use of protein supplement bypasses the cause of the low amino acid supply from silage diets in that it results from low microbial efficiency. A novel approach which seeks to improve microbial capture of nitrogen will be discussed in the general context of a more logical approach to the supplementation of high-digestibility silage.

South Wales Autumn-made Silage 1983-1985

P. M. Haigh

Welsh Office Agricultural Department, ADAS Sub-centre, Ty Glas Road, Llanishen, Cardiff CF4 5ZB, UK

Silage-making practices in respect of 188 samples of autumn-made silages from commercial farms in South Wales during 1983-1985 were investigated to discern the effect of wilting and/or silage additives on fermentation of bunker and big- bale silages.

Silages were primarily made during October in fine weather from perennial ryegrass pasture which had not been grazed for 6 weeks. On average 12.4 ha of pasture was cut for silage. Analysis of 120 samples of grass showed it contained 176 g kg-l dry matter (DM) with (g kg-' DM) 215 protein, 240 modified acid detergent fibre (MAD fibre), 78 water-soluble carbohydrate (WSC) and 95 ash. Most farmers attempted to pre-wilt herbage for 1 day prior to ensilage, and one- quarter of them made unwilted silage. Silage making was usually completed within 5 days of starting to cut, and herbage was ensiled mainly in a bunker using a precision-chop machine. One-third of the silages were ensiled in plastic bags. Silage additives applied to bunker silages were (litres t-') formic acid (3.9), formic acid+formalin (4.7), sulphuric acid+formalin (4-2), sugars (10) and inoculants (0.65 kg t-').

With bunker silages formic acid significantly reduced pH, and formic acid* formalin significantly reduced ammonia N content of silages compared with other treatments. Protein contents of acid/formalin-treated silages were significantly higher, and MAD fibre contents of formic acid& formalin-treated silages were significantly lower than other treatments. Pre-wilting herbage prior to ensilage


did not significantly increase subsequent silage DM content and significantly increased the pH of non-additive-treated silages. Unwilted formic acid *formalin-treated silages had a significantly lower ammonia N content and higher residual WSC than other treatments. Big-bale silages had a significantly higher DM content and pH than bunker silages, and ammonia N content was inversely correlated with increasing DM content.

With bunker silages it is suggested that only formic acid application either alone or in conjunction with formalin to unwilted silage was successful in producing well preserved silages, and that a herbage WSC content of 17 g kg-I would be necess- ary to achieve this. Similarly with big-bale silages additives were not used, and a WSC of about 25 g kg-l or DM content of about 300 g kg-' would be required.

The Digestibility of Grass Silage and its Effect on Milk Production

R. C. Rae," A. Reeve" and C. Thomasb

C I Jealott's Hill Research Station, Bracknell RG12 6EY, UK and bAnimal and Grassland Research Institute, Hurley, Maidenhead SL6 5LR, UK

The digestibility of grass silage is known to influence the performance of dairy cows, but responses have not been consistent due, possibly, to the range of silage and concentrate intakes and the preservation characteristics of the silages used. The objective of the present experiment was to assess the milk production response to increasing the digestibility of grass silage within a system where the cows were given relatively low levels of concentrates and had ad libitum access to the silage.

Two silages, of high and low digestibility, were prepared from the primary growth of ryegrass. A third silage, silage M, of intermediate digestibility, was prepared by mixing equal quantities of silages H and L in a forage mixing wagon prior to feeding each day. Fifty-four British Friesian cows with calving dates ranging from 4 October to 17 December were assigned to one of the three silages from day 15 of lactation until turnout to grass on 13 April (average duration 161 days). The silage was available ad libitum and was given on a treatment-group basis. Each cow was given 6 kg concentrates per day (18% crude protein, metabolisable energy=13-5 MJ kg-' DM) from day 15 of lactation until turnout. After turnout, concentrate feeding was stopped and the cows grazed ryegrass swards in a modified set-stocking system until the end of lactation.

The results are shown in Tables 1 and 2. Silage intake increased by 0.24 kg DM per digestible organic matter in the dry matter but the increase may have been partly due to differences in fermentation quality; silage L had poorer fermentation characteristics although the level of intake achieved was satisfactory. The increase in milk yield during the winter feeding period was a reflection of the higher ME intake, as was the substantial improvement in milk protein concentra-


tion. The results suggest that the amount of milk and milk solids produced from grass silage can be substantially increased by raising the digestibility of the silage.

TABLE 1 Composition of the Silages

Silage

H M L

Dry matter (g kg-I) 274 239 216 Ash (g kg-I DM) 98 95 90

650 615 Estimated DOMD" (g kg-') 705 Total N (g kg-' DM) 29 29 25 Ammonia N (g kg-I total N) 134 161 175

4.20 4.37 4.36 PH

"DOMD =945 -0.912 (MAD fibre).

TABLE 2 Feed Intake and Milk Production

Silage SE Digestibility effect

H M L Linear Quadratic

Winter period Silage intake (kg DM d-l) 11.6 10.3 9.4 Milk yield (kg d-I) 23-5 20.7 19.5 0-6 * * * NS Milk composition (g kg-')

Fat 43.2 40.9 42,3 1.1 NS NS Protein 31.9 29,4 28-8 0.7 * * * NS

NS Complete lactation * * Milk yield (kg cow-') 5887 5344 5241 231

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Agriculture group symposium recent developments in forage conservation and feeding