Effect of Arachis Oil on the Conservation of Heavily Wilted Herbage Ensiled in Plastic Containers 1.-Effect on silage fermentation quality, nutritive value, nutrient losses and intake by sheep by N. Jackson Department of Agricultural Chemistry, The Queen's University of Belfast, Belfast, BT9 6BB and Ministry of Agriculture for Northern Ireland

(Revised Manuscript received 5 April, 1971)

Arachis oil was added to heavily wilted herbage of approximately 40 dry matter, bejore ensiling in polyethylene containers. The oil was added at a mean level of 4 9 16% of the total dry matter ensiled. The mean dry matter loss from the two control and the two oil-treated silages was approximately 13%. There was a lower loss as inedible waste in the oil-treated silages and mould growth appeared to be inhibited by the oil. There was a lower percentage of butyric acid and propionic acid in the oil-treated silages than in the control silages, this effect being statistically significant. Ensiling resulted in a greater fall in digestibility of the control material than in the oil-treated material. The oil-treated silages had higher metabolisable energy contents than the control silages but the dry matter intakes o,f both silages by sheep were low.

Introduction

THE conservation of grass as silage has several major dis- advantages. The high dry matter losses are perhaps the greatest disadvantage, and in recent years it has been shown that the use of synthetic films to exclude air will greatly decrease the dry matter losses from the sil0.l-7 Also, the digestible energy content of silage is commonly fairly low. In a previous experiment8 it was found that silage produced by the addition of 4.9% arachis oil (on a dry matter basis) to wilted grass, had a higher metabolisable energy (ME) than control silage, and that the silage produced was of satisfactory quality and readily eaten by dairy cows and bullocks. The results suggested that there was no appreciable change in the composition of the fatty acids present in the arachis oil while the material was in the silos.

Hoffmann et al.9 found that arachis oil increased methane production by cattle and sheep in the rumen. A considerable number of further experiments have been carried out on the fate of vegetable oil or fatty acids in the ruminant and their effect on the utilisation of dietary energy by ruminants.10-17 These latter experiments have shown that dietary or infused linseed oil or fatty acids led to a marked reduction in the production of methane, the effect being greater with un- saturated than with saturated fatty acids. Czerkawski ef aI.lo found that when fatty acids were infused into the rumen, the reduction in energy loss as methane was greater than the incfeased loss of energy in the faeces with the result that the ME of the fatty acids was 104% of their heat of combustion. Their results and their reinterpretation of the results of other workers, some of whom used arachis oil,gJS led them to conclude that long-chain fatty acids arising from lipids, when absorbed by ruminants, are utilised with an efficiency much the same as that found in non-ruminant animals, i.e. about 80%, and retained by the body as fat. This suggested that the fatty acids, once absorbed, were not broken down to any appreciable extent, but were incorporated directly into the lipids of the tissues.

The results of the above investigations, mainly published since the results of the original experiments in which arachis oil was used as an energy source, prompted the author to carry out a further experiment in which arachis oil was again used. This experiment investigated in further detail the

J. Sci. Fd Agric., 1971, Vol. 22, August

effect of the oil on fermentation quality, and in a further comm~nicat ion~~ the fate of the added oil and its effect on the rumen fermentation of sheep is reported.

Experimental The herbage was cut with a flail mower in September and

was the second cut of a perennial ryegrass sward (L. perenne). The material was wilted to a dry matter content of approxi- mately 40 % in 30 h, collected with a forage harvester and filled into 4 rectangular containers (2 x 1.5 x 1.3 m) specialIy constructed using 500-gauge polyethylene. Wilted grass was put into silos 1 and 4 and wilted grass to which arachis oil was added was filled into silos 2 and 3. The oil was added and mixed thoroughly with the grass before it was placed in the containers. The ensiled material was consolidated by being trampled down. All silos were sealed by a heat-sealing process, in addition to which the seals were covered with a PVC waterproof adhesive tape. The average weight of dry matter put into the silos was approximately 190 kg. During the cutting, wilting and filling period the weather conditions were satisfactory. The weather was sunny with a maximum air temperature of 16"c and a minimum of 11 "c with a mean relative humidity for the two days of 86%. The arachis oil was applied at a rate such that its final concentration would be approximately 4 %. The actual concentrations were 4.26 % of the total dry matter ensiled in silo 2 and 4.06 % of the total dry matter ensiled in silo 3. Samples were taken from the grass or grass with oil, put into each silo for dry matter deter- mination and the dried material from each silo was bulked for gross chemical analysis and gross energy determinations. Samples of fresh material were used for the lipid analysis.

A number of samples, each of approximately 500 g of fresh material, were taken at random from the material being ensiled in silos 2 and 3, and the individual samples dried and extracted using petroleum ether (b.p. 40-6O"c) in order to assess the degree of distribution of the arachis oil within the mass.

The silos were opened in January, 1967. The weight of all the material present in the silos was recorded on the day of opening, and samples were taken for dry matter, chemical analysis and gross energy determinations. The material was then tightly packed and sealed in polyethylene sacks for

420 Jackson: Arachis Oil and Conservation of Heavily Wilted Silage. I

TABLE I

Composition and gross energy content of the ensiled material and edible silage dry matter

Control Oil-treated

Silo 1 Silo 4 Silo 2 Silo 3

Grass Silage* Grass Silage* y z silage* Grass Silage* + oil

Dry matter, % i S.E. of mean Ether extract, % i S.E. of mean Crude fibre. "/, . ~~.~

Crude protein; % Ash, % N-free extractives, % Organic matter, % True orotein. "/,

38.78(15)? 35.86(25) 40*14(14) 37.94(25) 41.65(14) 39.43(25) 43.48(15) 41.60(25) & 0.680 f 0.400 0.514 f 0.386 & 0.512 f 0.209 5 0.618 5 0.255 1.77 2.69 2.18 3.05 7.02(10) 7.21 5.97 6.59

29.22 30.97 30.00 32.18 i 1 .i26 29.08 29.90

& 0.428 29.08 30.33

12.09 12.75 12.19 12.70 11.40 12.09 11.89 12.37 _ .

13.26 14.03 12.59 13.21 12.54 i5.15 12.15 11.73 43.66 39.56 43.04 38.86 39.96 37.65 40.91 38.98 86.74 85.97 87.41 86.79 87.46 86.85 87.85 88.27 10.61 7.53 10.05 6.98 8.84 7.18 9.00 7.09

11.19 - 10.47 - 9.38 - 9.36 WSC, as glucose, % 17.20 4.08 15.68 3.26 11.22 5.02 11.99 3.66 Gross energy, kcal/g* * 4.24 4.24 4.24 4.24 4.45 4.48 4.45 4.48

Corrected true protein, % -

* Silage dry matter corrected for volatiles

t Figures in parenthesis are the number of samples on which the means and standard errors are based ** Determined on bulked material from two silos

digestibility determinations and voluntary feed intake studies. The methods used for chemical analysis were those of Jackson.6 In the computation of losses, volatile acids lost in drying were added to the N-free extractives fraction and the volatile bases to the crude protein fraction. The lipids in food and faeces were extracted using the procedure of Hopkins et a1.20 Metabolisable energy (ME) determina- tions were carried out on the grass ensiled and on both types of silage using wethers fed at the maintenance level, following the procedure of Anderson & Jackson.21

The voluntary feed intake for both types of silage was determined using three wethers and the ME of both types of silage was determined at this level of intake as well as at maintenance. In the intake trial the preliminary feeding period was 3 weeks. The intakes were recorded and the faeces and urine were collected over the last 10 day period, the amount of diet offered to the sheep being adjusted to give a 10% level of refused food.

Results The chemical composition and the gross energy values of

the material ensiled and of the silage removed are given in Table I. The standard errors for the dry matters of the grass, grass plus oil and the silages show that the material ensiled and removed was fairly homogeneous with respect to dry matter content. That the oil was reasonably well distributed throughout the,grass was indicated from the analysis of the individual samples. The large standard error of the ether extract content in silo 2 was mainly due to one sample which had an ether extract of 16.2%, while the range for the other samples was 4-14-7.83%.

The mean crude fibre content of the grass put into the control silos was 29.6% and that of the oil-treated grass was 29.1 %, while the corresponding mean crude protein contents were 12.1 % and 11 *6%, respectively. The mean dry matter contents of the material ensiled lay in the range 38.8-43.5%. The addition of the arachis oil to the grass caused a large increase in the ether extract of the ensiled material and a corresponding decrease in the other constituents. The gross energy of the material ensiled (as kcal/g) was increased by a mean value of 4 .9% with the addition of the oil, the mean calculated increase being 5-27;. The gross energies of the grass and silages were identical for the control silos and similar for the oil-treated grass and silage. The water-

soluble carbohydrate (WSC) content of the grass was high, the mean value being 17% of the dry matter. The residual WSC contents of the silages were low.

On opening the silos more waste was found in the control than in the oil-treated silages. There was a small amount of mould present in both types of silage, this being more pro- nounced in the control silages. Samples were taken for identification of the moulds and the results are presented in Table IT.

The mean contents of volatile acids, lactic acid, residual acidity and pH values together with volatile nitrogen and amino acid nitrogen percentages are given in Table 111. The pH values reflect the low organic acid production in wilted silage from which air has been effectively excluded. The levels of the volatile acids were low in both types of silage compared with values normally found for silage made in open trenches. The levels of lactic acid were high. The level of volatile nitrogen as a percentage of total nitrogen was low in all the silages. The butyric acid content was much higher in the control silages, a level of 1.8 % being recorded in silo 1, but the low volatile-N content does not indicate any major proteolytic clostridial activity in this silage. Traces of propionic acid and other volatile acids (isobutyric, isovaleric and valeric acids) were detected in the silages. These acids are produced by the de-amination of amino acids by the clostridial bacteria.22

TABLE I1 Identity and numbers of colonies which developed

in dilution plates Ten thousands/g of silage

Control Oil-treated

Silo 1 Silo 4 Silo 2 Silo 3 Organism

3 Penicillium sp. 21 - - Geotrichum sp. 4 23 4 2 Fusarium avenaceum - -

7 Cephalosporium sp. __ 67 -

Yeasts 24 666 43 133

- 1

-~

J. Sci. Fd Agric., 1971, Vol. 22, August

Jackson: Arachis Oil and Conservation of Heavily Wilted Silage. I 421

TABLE 111 pH values, volatile constituents and lactic acid contents

of the silages on a dry matter basis

Control Oil-treated

Silo 1 Silo 4 Silo 2 Silo 3 -

~ ~

pH value 4.45 4.25 4.25 4.30 Volatile N, %

of total N 9.65 7.72 7.11 6.79 Amino acid N, %

of total N 18.12 23.07 20.35 21.02 Residual acidity as

lactic acid. OL 4.43 5.30 4.92 5.12 Lactic acid, % 8.25 7.80 7.84 7.74 Aceticacid, % 0.77 1.05 1.57 1.05 Propionic acid, % 0.06 0.05 0.03 0.02 Butyric acid, % 1.80 0.82 0.11 0.45 Other volatile acids, % 0.05 0.03 0.01 0.07

TABLE IV Weights of dry matter filled into, and removed from silos, and dry

matter losses ~

Control Oil-treated

Silo 1 Silo 4 Silo 2 Silo 3

Dry matter put in as

Dry matter put in as

Edible silage dry matter

grass, kg 191.2 190.1 173.4 187.6

oil, kg - - 7.7 7.9 Total dry matter, kg 191.2 190.1 181.1 195.5

taken out, k g (corrected for volatiles) 133.6 148.1 148.5 169.5

Inedible silage dry matter

(corrected for volatiles) 37.8 10.6 7.0 1.7 Loss of dry matter, % 10.3 16.5 14.1 12.5

taken out, kg

In Table IV the weights of dry matter filled into and re- moved from the silos are presented, together with the per- centage dry matter losses. The inedible material taken out constituted 19.8, 3.9, 0.9 and 5.6% of the dry matter put into silos 1, 2, 3 and 4, respectively. A separate chemical analysis of the waste material from each silo was made for calculating losses of nutrients from the silos.

The mean losses of dry matter were 13.4 and 13.3 % from the control and oil-treated silos, respectively. The mean percentage loss of edible dry matter was quite high for both types of silage, being 26.1 and 15.6% for the control and oil-treated silos, respectively.

The mean digestibility of the dry matter of the grass ensiled as a control was 67-5 and for the oil-treated grass it was 65-7, while for the corresponding silages the mean dry matter digestibilities were 60.6 and 62.5, respectively. The percent- age digestibility of crude fibre was 76-7 and 74.8 for the grass and oil-treated grass, respectively.

The mean digestibility of the lipid materialz0 in the control grass was 19-3 while for the grass with added oil it was 61.6. In the corresponding silages digestibilities were 61 .6 and 77 -3, respectively. These data indicate the high apparent digestibility of the arachis oil. There was no evidence of any effect of the presence of oil on the apparent digestibility of any specific fraction of the grass or the silage.

The digestible nutrients present in the grass and silages are shown in Table V together with the ME values determined at the maintenance feeding level.

The mean total digestible nutrients (TDN) content for the grass was 63.9 and for the grass with oil added was 66.7, while for the corresponding silages the mean TDN values were 58.8 and 64.6. The mean starch equivalent (SE) value of the control silages was 37.9 and that of the oil-treated silages was 42.6. The mean percentage digestibility of the gross energy for the control silages was 63.2 while that for the oil-treated silages was 65.6. The mean ME values at maintenance of the grass and grass with added oil were 2.38 and 2.54 kcal/g respectively. The ME values at maintenance of the corresponding silages were 2.14 and 2.41 kcal/g.

The percentage losses of individual totaI and digestibte constituents from the silos are shown in Table VI. The per- centage losses from the total NFE fraction (19.4 and 24.6% for the control silages; 21-0 and 16.6% from the oil-treated silages) are in general lower than the losses reported in a previous experiment.8

Since the gross energy contents of the silages are virtually identical with those of the grass, the gross energy losses from the silos are very similar to the dry matter losses.

The data for the loss of digestible nutrients indicate that the losses of digestible dry matter were greater from the control silages (mean loss =34.6%) than from the oil-treated silages (mean loss =19.8%).

The largest loss was in the digestible N-free extractive fraction in both types of silage. The mean N-free extractive

TABLE V Percentage digestible nutrients, starch equivalents and metabolisable energy values of ensiled dry matter and silages

Control Oil-treated

Silo 1 Silo 4 Silo 2 Silo 3

Grass Silage Grass Silage Grass Silage Grass Silage

Ether extract Crude fibre Crude protein Ash N-free extractives Organic matter True protein Corrected true protein Total digestible nutrients Starch equivalent ME* (kcal/g)

0.34 22.40 7,45 4.18

33.15 63.34 6.28

63.77 45.15 2.38

-

1.65 22.42 8.00 4.16

24.39 56.46 2.80 6-58

58.52 38.18 2.14

0.42 1.88 4.31 5.77 3.66 5.09 23.00 23.30 21.76 22.08 21.76 22.26 7.51 7.97 6.77 7.79 7.06 7.97 3.97 3.91 3.99 4.19 3.86 3.74

32.62 23.56 28.84 22.83 29.33 22.02 63.55 56.71 61.68 58.27 61.81 58.72 5.95 2.60 5.00 3.07 5.09 3.03

5.43 - 5-42 - 6.16 - 64.07 59.06 67.07 65.23 66.39 64.08 44.62 37357 46.66 43.31 45.99 41.89 2.38 2.14 2.54 2.41 2.54 2.41

~ ~~

* Determined on bulked material from two silos J. Sci. Fd Agric., 1971, Vol. 22, August

422 Jackson: Arachis Oil and Conservation of Heavily Wilted Silage. I

TABLE V1 Percentage losses of total and digestible constituents from the silos

Control silages Oil-treated silages

Silo 1 Silo 4 silo 2 Silo 3

Total Digestible Total Digestible Total Digestible Total Digestible constitu- constitu- constitu- constitu- constitu- constitu- constitu- constitu-

ents ents -ents ents ents ents ents ents

Dry matter Ether extract Crude fibre Crude protein Ash N-free extractives Organic matter True protein Corrected true protein Total digestible nutrients Starch equivalent Gross energy ME Water-soluble carbohydrates

10.3 39.2 $30.2 +239.9

5 . 1 30.0 4 . 0 24.9 3 .1 30-4

19.4 48.5 11.4 37.7 3 3 . 1 68.8 4.0 26.8 - 35.9 - 40.9

- 37.1 10.2 -

83-4 -

16.5 30.1 +16*7 +248.9

10.5 21.1 1 3 - 1 17.3 12.4 23-3 24.6 43.7 17.1 30.5 42.1 66.0 1 3 . 1 19.4 - 28.2 - 34.4

16.5 - - 30.0

83.8 -

14.1 22.0 11.8 $6.0 11.7 16.8 8.9 5.7 9.9 13.9

21 .o 35.1 14.7 22.5 30.3 49.6 8.9 10.9 - 20.2 - 23.9

- 22.2 13.6 -

75.0 -

12.5 17.6 3.4 +20.6 8 . 1 10.8 8.9 2.1

15.5 16.0 16.6 34.2 12.0 17.6 31.0 48.4 8.9 7.7 - 16.3 - 21.1

11.9 - - 17,7

81.6 -

digestibility of the grass and grass plus oil was 70.2, and this fell to a mean of 61 a 0 for the silages. The mean ME content fell by lO.l%, i.e. from 2.38 kcal/g in the grass to 2.14 kcal/g in the corresponding silage, and by 5 e l % from 2.54 kcal/g in the grass plus oil to 2.41 kcal/g in the corres- ponding silage. The mean ME losses from the silos were 33.5% from the control silages and 19.9% from the oil- treated silages.

The mean feeding level attained by sheep fed the oil-treated silage was 19% higher than the feeding level for the control silage diet (Table VII). The mean intake of the oil-treated silage above the maintenance level was four times that of the intake above maintenance when the control silage was fed. The ME content of the oil-treated diet at the voluntary food intake level was 2.35 kcal/g compared to 2.22 kcal/g for the control silages. The methane energy loss was calculated using the equation given by Blaxter & Clappert0n.~3 This value for methane energy loss is probably high since work carried out by Czerkawski et aZ. lOJ1 indicated that a decrease in methane energy loss occurs when fatty acids or glycerides are added to a diet. The ME content of 2.35 kcal/g for the oil-treated silage is thus probably an underestimate of the ME content of the diet.

TABLE VII

Mean metabolic bodyweight of sheep their daily voluntary intakes of dry matter, digestible organic matter and metabolisable energy

Control Oil-treated S.E. of silages* silages* mean*

Mean bodyweight, kgW0,73 17.6 Daily dry matter

Daily dry matter intake, g/kgW0,73 45-0

Daily digestible dry matter intake, g/kgW0.73 28.3

Daily digestible organic matter intake, g/kg W0,73 25.4

Daily ME intake, kcal/kg WO.73 99.9

ME intake as a multiple

intake, kg 7.98

of maintenance 1.07

16.7 0.152 as.**

7.75 0.694 n.s.

46.5 2.80 a s .

29,4 2.00 n.s.

27.2 1 . 5 9 n.s.

109.3 7,21 ns.

1.27 0.066 n.s.

*

* Three sheep on each treatment ** n.s. = non-significant

The average urinary energy losses from the sheep were similar for both diets. The mean apparently digestible energy (ADE) percentages were 63 a 6 and 64.0 for the control and oil-treated silages, respectively. However, as a result of the higher gross energy content of the oil-treated silage (Table I) its ADE content was 2.87 kcal/g compared to 2.69 kcal/g for the control silage diet.

Discussion The percentage dry matter losses in this experiment were

lower than in the previous experiment* in which the mean dry matter losses for control and oil-treated silage were 21.1 and 19*9%, respectively. The mean value in the present experi- ment of 1 3 . 3 % was, however, higher than those found in previous experiments where wilted herbage was enclosed in polyethylene film. Brown & Kerr3 reported a mean loss of 6 -7 % for heavily wilted herbage ensiled in polyethylene-Iined trench silos and Jackson6 reported a mean loss of 6 - 5 % for heavily wilted herbage completely sealed in polyethylene. The addition of oil to the grass reduced the amount of inedible waste in the silage. The mean losses as inedible waste were 12.7% and 2 . 4 % for the control and oil-treated silages, respectively. The lower average losses as inedible waste in the oil-treated silage suggest that the presence of the oil may have had an inhibiting effect on the development of yeasts and other organisms in the ensiled material, but the data in Table I1 do not give any definite quantitative indication of such an effect. However, this suggestion is supported by the fact that when stored for 4 months in sealed polyethylene sacks a visual assessment indicated that in the control silages about 50% of the material was heavily contaminated with moulds while in the oil-treated silage only about 10% of the material was spoiled by moulds.

The analytical data in Table I show that the percentage crude fibre increased by two percentage units in the control silages and by one percentage unit in the oil-treated silages. This indicates a smaller differential loss of other constituents in the ail-treated silages than in the control silages, suggesting that fermentation losses have been depressed by the oil. This effect is again evidenced by the mean decrease in the nitrogen-free extractives content of 4 . 1 percentage units in the control silages and the mean decrease of only 2.1 percentage units in the oil-treated silages. However, these analytical differences are not reflected in the total dry matter losses (Table IV) from the silos, which showed no significant differ- ence between silos.

J. Sci. Fd Agric., 1971, VoI. 22, August

Jackson: Arachis Oil and Conservation of Heavily Wilted Silage. I 423

The presence of the oil has not reduced the fermentation losses of WSC. The results of the losses of WSC and the products of fermentation indicate that the homolactic fermentation was the major pathway of sugar utilisation. There was a considerable amount of saccharolytic clostridial activity in control silo 1.

The presence of the oil also appears to have inhibited the breakdown of true protein, this fraction decreasing by only 1 . 8 percentage units in the oil-treated herbage compared to 3 .1 percentage units in the control silage. The overall effect of this is seen in the mean TDN loss of 5 - 1 percentage units for the control silos and 2.0 percentage units for the oil-treated silos (Table V). The lower losses of digestible dry matter in the oil-treated silages is a reflexion both of the lower loss of inedible dry matter and the lower fall in digestibility on ensiling compared with the control silages.

On average, addition of arachis oil at ensiling increased the ME contents of the diets (grass and silage) by 8 a 4 % compared with the previously reported average increase of 6 . 9 % for grass with added arachis oil and the resulting silage.8 The mean ME content of the oil-treated diets (grass and silage) was 2.43 kcal/g compared with 2.25 kcallg for the control diets. The ME content of the arachis oil was calculated as 6.58 kcal/g compared with a gross energy of 9.52 kcal/g. The calculated percentage of ME of the arachis oil was thus 69.1%. This value indicates that the added oil was effici- ently metabolised by the ruminant. Since any effect of oil

addition to the diet in reducing the methane energy Iosslo was not taken into account in the ME determinations the apparent metabolisability of the added arachis oil may be greater than this calculated value.

There was a slightly higher feeding level attained with the sheep fed the oil-treated silage but the difference was not statistically significant. The dry matter intakes of the silages were much lower than the values calculated for roughages based on the metabolisability of food energy.Z4 Low intakes of silage by sheep have been reported by other workers.25

A separate investigation was carried out on the fate of the individual fatty acids present in the arachis oil and the effect of the oil on the rumen volatile fatty acids of sheep. The results1Q suggest that little change occurs in the added oil. A similar observation was made by Jackson & Brown.8 No significant effect was found with the addition of oil on the molar proportions of the volatile fatty acids in the rumen liquor of sheep fed the two silage diets.

Acknowledgments

The author thanks the Director and Trustees of the Agri- cultural Research Institute of Northern Ireland, Hillsborough, for providing facilities for this work and C. Black, W. Crawford and T. Poland for technical assistance.

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