Preservation of moist hay in miniature bales treated with propionic acid

J. \rorrd Prod. Rur. Vol. 14. PP. X-33 Q Pergamon Press Ltd 1978. Printed I” Great Britain

HAY IN MINIATURE BALES TREATED WITH PROPIONIC ACID PRESERVATION

D.

OF MOIST

L. EASSON* AND M. J. NASH

The Edinburgh School of Agriculture, Edinburgh, Scotland Abstract-In 2 experiments, propionic acid was applied by hand-sprayer to partly dried hay which was made into miniature bales of about 1 kg. In an experiment in which the hay moisture content was 51%, acid was applied at O%, lY/,, 2%. 4%, 6% and 8% by weight. Bales with less than 4% acid showed severe heating, moulding, and losses of dry matter and nutrient content within a few weeks. Bales with 4% acid or more were still well preserved after 3 months. In a second experiment hays of 32% and 41% moisture showed moulding at 0.5% and LO:/, acid respectively, but slight or no moulding at 1.0% and 1.5% acid. At 48%. 59% and 767; moistures the lowest acid levels used, 2%, 3% and 3.5% respectively, all prevented moulding. It was concluded that acid treatments of 1%. l%-1.5%. and 2?/, for hays of 30%. 40% and 50% moisture respectively were on the margin between being effective and ineffective in the preservation of hay stored under experimental conditions.

INTRODUCTION

the use of propionic acid as a preservative for moist hay (NASH and EASSO~J,1977), using conventional sized bales (90 cm x 45 cm x 35 cm) treated with acid through an applicator attached to the baler, could not establish precise levels of acid required to preserve hay of different moisture contents, due to wide variations in the moisture content of the hay and irregular acid distribution within the bales. As moisture content and acid treatment level are the two most critical factors affecting fungal development, two further experiments were carried out in which the variations in these factors were reduced. This was achieved by using smaller quantities of hay, as miniature bales applying the acid with a hand sprayer, and storing (20 cm x 20 cm x 20 cm) compressed to similar densities as conventional bales. The aim of these experiments, which are described here, was to establish the levels of acid required to preserve hay at different levels of moisture, from 80% down to 20%. FIELD experiments

into

METHODS

Experiment I (1971) A small area of L.&urn perenne was cut at the flowering stage and tedded by machine and by hand labour to ensure as rapid and even drying as possible. When at a moisture content of about 50%, this being considered near the upper limit likely to occur in commercial haymaking, the hay was taken to the store, mixed thoroughly, and divided into 6 equal lots. Each of these was spread as a 1Ocm to 15 cm deep layer on the floor, and treated as evenly as possible with propionic acid using a hand sprayer delivering a fine spray. Draughts were excluded to reduce the risk of acid loss. Treatment levels of Ox, lx, 2%, 4x, 6% and 8% by weight were applied, each lot being turned 2 or 3 times during application. After further mixing, each lot was weighed into 4 equal portions in readiness for baling. Grab samples were taken (i), from the untreated hay, after the initial mixing, to provide a single sample from which an overall water-soluble carbohydrate determination was carried out in triplicate and, (ii) from each of the 6 lots immediately after the acid treatment and second mixing, for moisture content and pH determinations in duplicate. * Present address: Agricultural Research Institute of Northern Ireland. Hillsborough. Co. Down 25

D. L. EASSONand M. J. NASH

26

The bales were made using a specially constructed mini-baler comprising a wooden chamber with one end open and the other closed. When the chamber was filled with hay a sliding base was inserted in the open end. This was compressed against the hay using a hydraulic jack until the required density was reached. Two strings, which had previously been placed in the chamber, were used to tie the bale before its removal. Four replicate bales were made at each treatment level; during storage these were arranged in four randomised blocks. Each bale was trimmed, to remove any loose ends, and then weighed before being placed with 5 other bales in insulated compartments of a polystyrene box. Heat loss from the mini-bales, which have a relatively large surface/volume ratio in comparison with conventional sized bales, was thereby reduced. A loose fitting lid was placed over each box. Mercury-in-glass thermometers were inserted through these and into the centres of the bales. The boxes were stored in an insulated shed for a period of 3 months. Temperatures were recorded daily for each bale, and at the end of storage each bale was reweighed and at the same time its visual appearance noted. Using the corer designed by ALEXANDER et al. (1969), 3 or 4 cores were taken from each bale, this amounting to about 25% of the total volume of the bale. Each cored sample was mixed and sub-sampled for dry matter, pH and water-soluble carbohydrate determinations. The latter were carried out according to the method of MCDONALD and HENDERSON (1974). Moisture contents were determined using the standard oven-drying technique, i.e. 24 hr at 100°C. Experiment II (1972) Bales were made at 5 moisture levels, ranging from about 76% in the case of freshly cut grass to about 30% for the driest hay (Table 1). At each moisture a different range of acid treatments was used, encompassing levels above and below those which were thought necessary for preservation. Steps of 0.5% were chosen, since it was clear that these would give more precise data on preservation than the wider steps used in Experiment I. However, in the case of highest moisture grass, 1% steps were used giving the advantage of an extended range of treatments for material which would not normally be considered capable of aerobic storage. To obtain hay close to the desired moisture levels, samples were dried within 3 to 1 hr using a hot air fan drier. The results from 2-3 samples daily were used to predict when the required water content would be obtained. The same procedure for sampling, treating and baling was adopted as described for Experiment I. In addition, the acid treatments received by the hay were checked by means of a simple method of acid extraction. A 10 g chopped sub-sample was placed in a polythene bag along with 100 ml of deionised water and left to soak overnight at room temperature. A 10 ml aliquot of the resulting solution was then titrated with N/10 NaOH to the end point with phenolpthalene indicator. Each determination was carried out in triplicate. An improved design of mini-baler was used, which enabled bales to be made more quickly. During baling it was found, as with normal field baling, that the drier hays could not be compressed to the fresh matter densities obtained with high moisture content hay. To improve the accuracy of comparison between treatments, therefore, bales were made at similar dry matter densities-at 0.1 g/cm3. TABLE 1. DESIGN OF EXPERIMENT II Moisture level (%) 16

nil

59

x x

48 41 32

X X X

0.5

1.0

Propionic acid treatment (per cent by weight) 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

x

X

X X

X X

X X X

X X

X X

x x

x

X

X

x x

x

5.5

6.5

7.5

x

x

x

Preservation of Moist Hay in Miniature Bales

27

TABLE2. RESULT FOREXPERIMENT I Acid treatment (“/b) Initial MC% Final MC% Initial pH value Final pH value WSC in DM. loss O0 DM loss % Moisture loss Y, Visible moulding

nil

lo’ /ll

2”’ /0

4%

6%

8%

LSD

50.4 21.5 6.5 8.2 91.0 30.1 81.2 severe

51.0 24.8 5.5 8.1 95.1 31.3 78.3 severe

51.1 25.6 5.0 8.3 9.5.9 25.1 15.6 severe

50.2 43.8 4.6 4.9 + 10.2 3.4 25.1 nil

51.3 45.7 4.4 4.7 10.0 9.0 21.3 nil

51.0 45.9 4.3 4.7 +O.l 4.4 22. I nil

12.9 9.1 1.3 (P = 0.05)

MC = moisture content; WSC = water-soluble carbohydrate;

DM = dry matter.

RESULTS

Experiment I The results of Experiment I are given in Table 2. All the bales of the nil, 1% and 2% acid treatments were black in colour. These bales showed severe moulding and rotting, with dry matter losses of 25% to 30%, and almost complete loss of water-soluble carbohydrates. pH values exceeded 8.0 in every case. From the mean results for temperature it will be seen that heating occurred in the nil, 1% and 2% treated bales (Fig. 1). In the untreated bales initial peaks of from 20” to 25°C occurred after 2 days, this being followed by a second peak of from 30” to 35°C after 6 to 7 days. In contrast, the 1% and 2% treated bales showed negligible initial heating, while secondary heating, up to 3040°C in some individual bales, was delayed until 2 weeks and 334 weeks after storage respectively. Nevertheless, the losses in the 1% and 2% treated bales were not significantly below those in the untreated bales. In the bales treated with 4%, 6% and 8% acid, there was little evidence of heating, even during the first few days of storage, and no moulding was visible. The losses of dry matter were small with the 4% and 8% treatments, but were as high as 95”, with the 6% treated hay. Apparent losses of water-soluble carbohydrate ranged from - 10% to + 10%. Experiment 11 For convenience, the results of this experiment are considered in 2 sections, ‘high moisture’ hays of 76%, 59% and 48% moisture content, and ‘low moisture’ hays of 41% and 32% moisture content (Table 3).

0

1

2

3

L

Weeks

0 - untreated 0 - 1vOo/o acid Each

* - 2.0’/. * - 1*0% line

a mean

of

four

replicate

bales

FIG. 1. Mini-bale temperatures, Experiment 1.

acid acid

5

D. L. EASON and M. J. NASH

28

TABLE 3. RESULTSFORHIGHMOISTURE HAYSIN EXPERIMENT II (MEANSOF 4 REPLICATES)

Moisture level 76% Acid treatment % Initial MC 9; Final MC % Initial pH value Final pH value WSC in DM, loss % DM, loss % Moisture, loss % Visible moulding

Nil 77.9 78.6 5.6 8.1 56.9 61.2 98.9 severe

3.5 15.3 72.4 4.4 4.2 20.2 7.9 11.9 nil

Initial WSC 28.3: 4.5 76.7 72.3 4.1 4.1 23.2 3.3 29.4 nil

5.5 74.9 72.2 4.1 4.0 22.5 11.8 32.0 nil

6.5 76.2 73.5 4.0 3.9 18.2 6.2 33.3 nil

Moisture level 59% Acid treatment Y0 Initial MC % Final MC % Initial pH value Final pH value WSC in DM, loss % DM, loss % Moisture, loss % Visible moulding

nil 61.4 54.7 5.6 8.7 98.9 56.4 65.5 severe

3.1 58.2 55.1 4.7 4.5 20.4 9.3 19.9 nil

nil 52.1 17.4 6.5 8.0 94.3 29.4 86.8 severe

2.2 41.2 40.7 5.2 4.1 + 2.4 3.7 25.8 nil

LSD

13.1 3.6 28.5 (P = 0.01)

Initial WSC 29.89, 3.6 59.0 56.2 4.6 4.4 9.5 9.2 19.0 nil

4.2 60.0 55.0 4.3 4.4 4.4 4.9 22.4 nil

4.6 56.6 53.5 4.5 4.4 24.8 12.0 22.1 nil

Moisture level 487’0 Acid treatment % Initial MC % Final MC % Initial pH value Final pH value WSC in DM, loss 70 DM loss % Moisture, loss % Visible moulding

1.5 73.4 72.0 4.0 4.0 20.2 15.0 38.1 nil

5.0 58.3 56.1 4.3 4.3 10.7 11.5 19.2 nil

LSD

29.2 7.2 47.4 (P = 0.01)

Initial WSC 24.1Y0 2.8 46.4 40.7 5.0 4.6 -t 1.4 2.9 22.9 nil

MC = moisture content; WSC = water-soluble carbohydrate;

3.2 46.8 39.1 4.8 4.6 +9.1 0.9 27.5 nil

3.8 46.4 41.2 4.8 4.5 10.3 5.3 22.8 nil

4.2 48.1 39.9 4.6 4.6 +5.5 0.1 28.0 nil

LSD

21.1 5.7 9.9 (P = 0.01)

DM = dry matter.

High moisture hays. All the untreated hays showed severe moulding and decomposition. By far the highest mean dry matter loss, 61.2%, took place in the fresh grass with moisture contents of 76%, but the highest storage temperatures were reached in the 59% moisture bales, 6 days after storage (Fig. 2A). All the control bales showed the same pattern of heating, with initial temperature peaks occurring at 1 to 4 days, followed by secondary but higher peaks at 7 to 9 days. All the acid treatments significantly reduced losses of dry matter, water-soluble carbohydrates and moisture; the temperatures did not rise above the ambient, nor was there any visible moulding apparent in any of the bales. Water-soluble carbohydrate losses were reduced to insignificant levels, even by the lowest levels of acid, i.e. by the 2.2% and 3.1% treatments on the 48% and 59% moisture hays respectively. At the 76% moisture level, however, about 20% of the soluble sugar was lost at all acid levels. Mean dry matter losses were also relatively high, both at the 76% and 59% moisture levels, reaching 10% to 15% in some cases. At the 48% moisture level the mean dry matter losses were generally low, ranging from 0% to 5%. The pH values of the acid treated hays tended to show a slight fall during storage whereas those in the mouldy bales rose considerably. Low moisture hays. The untreated bales were again severely mouldy with almost complete loss of water-soluble carbohydrates, and, with dry matter losses of 21% and 30% at the 32% and 41% moisture levels respectively. Heating took place only to a limited extent in these bales for the first 10 days of storage (Fig. 2B, 2C), during which time the ambient temperature was between 10°C and 15°C. Heating became more noticeable, however, during the third and fourth weeks, probably because at the beginning of this

Preservation of Moist Hay in Miniature Bales

29

d0 ‘C

A

20

High moisture

0

I

I

1

2

I

I

I

3

k

5

LO OC 0 Ll’l,

moisture

2o

0 10 “C

C 32%

moisture

2o

0 0

Weeks - Ll% c- 4%

o - 76% moisture, - 76Vo moisture,

nil acid 3.5% acid

*- 59*Io moisture, A - L~*/o moisture, A - LflYo moisture,

nil acid nil acid 2.Oo/o acid V - 32% moisture,

l

Each

line

a mean

of

four

moisture, moisture,

nil acid 1.0’/0 acid

41% moisture, - 32%moisture, 0 - 32’/* moisture, 1.0*/o acid

1.5% acid nil acid 0.5 % acid

l

replicate

.-

l

bales

FIG. 2. Mini-bale temperatures, Experiment II. period there was a significant rise in ambient temperature. It will be noticed that even in the treated batches, which underwent no biological heating, there was a slight rise in temperature at this time. The lowest acid rates at both the 40% and 30% moisture levels, i.e. 1.07; and 0.5”; acid, were unable to prevent moulding, although in both cases these treatments delayed the onset and reduced the degree of heating. All losses in these bales were high, and were not significantly below those of the untreated bales in most cases. On the other hand, in one of the 30% moisture bales which received 1% acid, slight visible moulding was present which may have been the cause of the slightly increased heating and loss of dry matter. Higher acid levels either completely or almost completely prevented visible moulding and reduced heating to insignificant levels, although water-soluble carbohydrate losses tended to be high; of the order of 30%. These losses, however, were still significantly below those from the untreated and lowest acid treated bales. Propionic

acid recovery

and pH values

The results of the acid determinations are shown itl Fig. 3. At the 0.5y0 and l.O:,; rates of application very little of the acid was recovered by the extraction method used, but as the level of application increased so did the proportion of acid recovered. Above about 4% acid application there was a consistent recovery of 90% to 957;. However, the results for any one acid application rate varied considerably. Also titration

D. L. EASSON and M. J.

30 TABLE

NASH

4. RESULTSFOR LOW MOISTUREHAYS IN EXPERIMENT II (MEANSOF 4 Moisture level 41%

Acid treatment 7: Initial MC % Final MC % Initial pH value Final pH value WSC in DM, loss % DM, loss % Moisture, loss % Visible moulding

nil 41.0 19.4 6.0 8.2 88.1 30.2 75.9 severe

Imtlal WSC 24.3:”

1.0 41.3 24.2 5.6 7.5 86.1 17.6 62.4 moderate

1.5 40.5 31.9 5.3 5.1 32.0 0.4 31.0 nil

2.0 41.6 32.0 5.2 4.9 25.2 +1.0 33.0 nil

2.5 42.1 31.8 5.0 4.9 16.1 + 2.2 34.5 nil

Moisture level 32% Acid treatment % Initial MC “/‘, Final MC % Initial pH value Final pH value WSC in DM, loss % DM, loss % Moisture, loss % Visible moulding

nil 33.0 18.8 6.1 7.3 92.1 21.4 63.2 severe

REPLICATES)

3.0 41.0 32.1 4.9 4.7 30.3 0.8 32.2 nil

LSD

29.7 5.4 3.2 (P = 0.01)

Initial WSC 24.3%

0.5 30.2 18.2 5.9 6.7 78.1 18.7 58.0 moderate

1.0 30.4 24.6 5.8 5.7 36.4 6.4 30.0 slight

1.5 33.3 24.5 5.5 5.6 35.2 0.2 34.8 nil

MC = moisture content; WSC = water-soluble carbohydrate;

2.0 31.0 24.2 5.3 5.2 24.0 2.7 26.0 nil

LSD

34.2 9.2 (P 2.0,)

DM = dry matter.

was required even with the untreated hay, indicating the presence of natural acidic extracts. The initial pH vaIues also give an indication of the acid received by the hay (Figure 4). These follow a regular descending pattern with increasing acid application at all moisture levels and do not confirm the low acid levels on the hays which the recovery figures mentioned above would suggest. DISCUSSiON

AND CONCLUSION

Mini-bales have been advocated in the U.S.A. as part of a possible new system of handling hay (ANON., 1972). At Edinburgh mini-bales have been used solely as a research tool, mainly with the object of eliminating unwanted variables. In earlier work with conventional sized bales (NASH and EASSON, 1977) treatment with propionic acid only preserved patches within bales. This inefficient preservation was attributed to a combination of irregular distribution of the acid within the bales and natural variations in

E a

0 0

FIG. 3. Apparent

I

2

3

4

Propionic

acid

awlication

recovery of propionic

5

6

7 %

rate

acid from hays in Experiment treatment.

II 24 to 48 hr after

Preservation of Moist Hay in Miniature Bales

6.5!

31

Moisture levels * - 76%

PH

2

3

L

5

Propionic acid application

6

1

rate

8%

FIG. 4. pH values in Experiment II 24 hr after treatment.

the moisture content of the hay. As nothing was known of how much acid actually reached each part of these conventional sized bales, or of the precise extent of the moisture variations, no conclusions could be drawn concerning the levels of acid required for preservation. In the exploratory work of Experiment I there was either uniform preservation or uniform moulding of the bales, presumably due to a more uniform moisture content and acid treatment made possible when using relatively small quantities of hay. In the conventional bales used in earlier experiments (NASH and EASSON,1977) the 2% and 4% acid treated high moisture hays (43% moisture) differed slightly in the proportion of the hay which was mouldy, but not in any other major respect. The equivalent mini-bale treatments, however, resulted in a clear differential between the ‘inadequate’ 2% treatment, which showed severe deterioration and high losses, and the ‘adequate’ 4%’ treatment which was well preserved. The storage temperatures in the untreated mini-bales were much lower than those in the corresponding small batches of untreated conventional bales. This would suggest that the level of insulation round the mini-bales with their relatively large surface to volume ratio was inadequate. Also, the densities of the mini-bales were only 74% to 88% of that of corresponding conventional bales, and this may have contributed to the lower temperatures. However, in spite of the lower temperatures the untreated minibales showed losses as high, or higher, than the corresponding conventional bales. NELSON (1966, 1968, 1972) also found that bales of low density had lower temperatures. He concluded that density had little effect on both the extent of moulding and losses, and agreed with GREGORY et al. (1963) that the moisture content was the fundamental factor influencing deterioration. It is possible that the lower temperatures, as found by the present authors, may have influenced the particular species involved in the fungal succession, but they are unlikely to bear any relationship to the amount of acid required for preservation because any heating at all simply indicates that the acid treatment has failed. In both Experiments I and II the treatments which did not prevent moulding at least delayed its onset for a number of days. LORD and LACEY (1975) have found a species of fungus, Paecilomyces varioti, which is capable of metabolising low concentrations of propionic acid. It is possible, therefore, that at the low application rates there was an initial slow growth of fungi which, although partly inhibited, were still capable of metabolising acid. Eventually they would become sufficiently free from inhibition to make rapid growth. While the results of Experiment I indicated that an application rate of between 29;

D. L. EASSON and M. J.

Moisture content

3*

/

0

0

Acid treatmmts being effective

100

Propionic

mouldy

marginal

*

Experiment

II

l

Moisture

1,

application

I

hay ceases.

3

acid

Experiment

0

on the margin between and ineffective

2

1

0

NASH

content

5 %

rate mould-free *

0 atwhich

mould

0

grovrth on

I Waite, 19b9 1

FIG. 5. Elective, marginal and ineffective propionic

acid treatment

levels.

and 4% acid would be needed to preserve hay at 50% moisture, Experiment II showed that for this moisture content the 2% treatment must in fact have been marginal, because the slightly higher level of 2.2% allowed effective preservation of hay at 48% moisture. The 1% acid treatment at 32% moisture also proved to be marginal, as one of the four replicate bales showed some moulding. At the next higher moisture level, 41x, the 1.0% treatment was mouldy throughout all the bales while the 1.5% treatment was well preserved so that acid treatments between these would be marginal. The results of this work therefore suggests that at the moisture contents of about 500/, 40% and 30x, propionic acid application rates of 2%, 1.0% to 1.5% and 1.0% respectively are on the margin between being effective and ineffective in preventing the moulding of hay (Fig. 5). LEWIS (1951) working with 300g samples of hay of 40% moisture stored in glass jars, found that an acid application rate of between 2% and 3% was. required for effective preservation. SHUKKING(1972), experimenting with loose hay stored in insulated containers 28 cm x 22 cm’x 26 cm found that application rates of 0.8x, 1.5x-2% and 2.5x-3% provided mould-free preservation at moisture contents of 31x, 40% and 50% respectively. While the above workers suggest acid requirements in excess of those established in the Edinburgh experiments, work published more recently has suggested lower requirements for preservation. CANDLISHet al. (1973), found that acid treatments as low as 0.1% prevented moulding and reduced heating, in hay with a moisture content of 40%. However this result related only to the first 3 days after baling and not to any subsequent changes. A more comprehensive series of trials carried out by KLINNER (1976) showed that net acid levels of 0.5% to 1.0% would give a low risk of heating in hay of 29% to 35% moisture content. KNAPP et al. (1976) also found that 1.0% propionic acid was sufficient to preserve hay of 34% moisture, although in this case the hay was treated after, and not during, baling. The slightly higher acid requirements found in the present mini-bale work compared to those quoted by KLINNER (1976) and KNAPP ef al. (1976), may have been due to volatization of acid during application. All the workers mentioned above have reported

Preservation of Moist Hay

in MiniatureBales

33

problems caused by losses from this source. The relatively fine spray used in the Edinburgh work may have aggravated the problem as KLINNER (1976) has suggested that losses can be expected to be higher with a fine spray rather than one with coarser droplets of about 800 p diameter. Unfortunately, the method used at Edinburgh for the propionic acid extractions was not very reliable, particularly at the lower acid levels where the results were more critical. The true extent of the volatile losses cannot therefore be ascertained. The very low recovery of the acid at the application rates between 0% and 3% could have been caused by the formation of less soluble calcium salts once the acid had been absorbed by the hay (LESSARDand MCDONALD, 1966). However, despite these low acid recoveries, the initial pH values over the whole range of treatments shows a clear relationship with the quantity of acid applied. The losses due to volatilization may not therefore have been as high as the recovery figures would suggest. Although the acid treated bales at the two highest moisture levels, 760,; and 59”, were free from moulding, such material could hardly be called ‘hay’. The relatively high losses of dry matter and water soluble carbohydrates which occurred in these bales cannot be easily explained. Under such high moisture conditions bacterial activity is likely to occur, but even this should have been prevented by the high hydrogen ion concentration at the higher acid levels (pH 4..0). The occurrence of any anaerobic fermentation would have resulted in the production of organic acids, but none other than propionic acid was found when samples were analysed using a silica gel chromatographic column. Aerobic growth, on the other hand, would have led to oxidative changes and a rise in pH value, but again the results were negative. Clearly further work is necessary to elucidate these points. This work has proved the value of mini-bales as a research tool for work on hay, and permitted the establishment, with reasonable confidence, of the minimum levels of propionic acid needed to preserve hay under experimental conditions. Acknowledgements-We are grateful to BP Nutrition (U.K.) Ltd. for financial assistance, to Dr. P. McDonald and Dr. A. R. Henderson of the Biochemistry Department of the Edinburgh School of Agriculture for laboratory assistance and to the staff of the School’s farms for practical help. Also to Dr. B. D. Witney and staff of. the Engineering Department for constructing the Mini-Baler Mark II.

REFERENCES ALEXANDER, R.

H., MCGOWAN, M. and STEWART,D. (1969) A manually operated tool for sampling hay bales in stacks. J. agric. Engng. Res. 14, 89-91. ANONYMOUS (1972) Experiments with mini-bales, U.S.A. Power Farming 48, 23. CANDLISH, E., CLARK, K. W. and INGALLS,J. R. (1973) Organic acid treatment of hay. Can. 1. Anim. Sci. 53, 513-518. GREGORY,P. H., LACEY,M. E., FESTENSTEIN, G. N. and SKINNER,F. A. (1963) Microbial and biochemical changes during the moulding of hay. J. gen. Micro&o!. 33, 147-174. KLINNER,W. E. (1976) Mechanical and chemical treatment of grass for conservation. Report 21, nat. fnsr. agric. Engng, Silsoe, England KNAPP,-W. R., Hotr, D. A. and LECHTENEERG, V. L. (1976) Propionic acid as a hay_ _ preservative. Aqron. J. 68, 12%123. LESSARD,J. R. and MCDONALD, P. (1966) A silica gel chromatographic procedure adapted to liquid-scintillation counting of 14C labelled oreanic acids from Dlant material and silaae. J. Sci. Fd Aaric.. 17. 257-263. LEWIS,B.-D. (1951) Preoention-of mould on high *moisture hay with emph&is on the fatty kids as fungicidal agents. M.Sc. Thesis, Michigan State University, U.S.A. LORD, K. A. and LACEY,J. (1975) Prevention of moulding in damp hay. Rorhamsred Ann. Rep. 1974, Part 1, 159. MCDONALD, P. and HENDERSON,A. R. (1974) Determination of water-soluble carbohydrates in grass. J. Sci.

Fd Agric. 25, 791-795. NASH, M. J. and EASSON,D. L. (1977) Preservation of moist hay with propionic acid. J. stored Prod. Res. 13, 65-75. NELSON,L. F. (1966) Spontaneous heating and nutrient retention of baled alfalfa hay during storage. Truns. Am. Sot. agric. Engrs. 9, 509-512.

NELSON,L. F. (1968) Spontaneous heating, gross energy retention and nutrient retention of high density alfalfa hay bales. Trans. Am. agric. Engrs. 11, 596-600. NELSON,L. F. (1972) Storage characteristics and nutritive values of high density native hay bales. Trans. Am. Sot. agric. Engrs. 15, 201-205. SHUKKING, S. K. (1972) Treatment of silage and hay with organic acids. Unpublished report. Wageningen. WAITE, R. (1949) The relationship between moisture content and moulding in cured hay. Ann. uppl. &of. 36, 496-503.