Laboratory evaluation of ensiled olive cake, tomato pulp and poultry litter

Poultry litter collected from a commercial broiler house, bedded with chopped cereal straw, was used. The material was screened before it was ensiled with different proportions of tomato pulp (trial 1) or crude olive cake (trial 2). In a third trial, the effect of urea level [0, 30, 50, 70% (w/v) urea solution at the rate of 100 ml per kg olive cake DM basis] on the nutritive value of ensiled crude olive cake was studied. Finally, dry matter and crude protein degradability of tomato pulp, poultry litter and olive cake were determined using rumen-fistulated Damascus goats.

Addition of poultry litter at ensiling resulted in a significant increase in nitrogen content and pH values of all mixtures. Incorporation of poultry litter in the mixtures containing tomato pulp decreased the in vitro digestibility of the mixtures, whereas the opposite was the case with olive cake mixtures. Treatment of olive cake with urea solution increased the nitrogen content of the silage, but its effect on in vitro digestibility was small. There was no mould in any of the silages, and all had aroma and colour ranging from good to very good. With the exception of silage treated with urea all others had pH values below or close to 5. In only one initial mixture there was very small amount of butyric acid. Fatty acid concentration was increased with ensiling.

It is concluded that the ensiling technique can be safely used for long storage of olive cake and tomato pulp, and that mixing of olive cake with other by-products at ensiling not only gives a more balanced silage mixture, but it also results in better silage characteristics.

Crude olive cake, a mixture of skins, pulp and seeds from olives after the extraction of oil, is available in appreciable quantities in the Mediterranean area (Sansoucy 1987), comprising around 35% of the processed olives. Despite the severe shortage of animal feedstuffs in most Mediterranean countries, the use of olive cake in ruminant animal diets is limited because of its low nutritive value and seasonality. Deep stacking of olive cake near the processing plants results in a considerable deterioration (mould formation) of the material and in wastage of nutrients.

Different chemical (application of 4-6% NaOH, NH₄OH) (Nefzaoui et al 1983) and physical (removal of stones after solvent extraction of oil) methods have been used for attaining a greater and improved use of the by-product.

Tomato pulp, comprising about 7% of the tomatoes processed for juice or paste production, is another by-product of high moisture content, but of good nutritional value (NRC 1989). Because of its very high moisture content, the costs of long distance transportation, dehydration and storage are prohibitive. The material ferments and sours quickly and ensiling it with by- products of high dry matter content like Poultry litter may be proven an ideal, simple and of low cost processing procedure for its utilization.

In previous studies, high moisture agro-industrial by-products like citrus pulp, grape marc and sugarbeet pulp were successfully ensiled with screened poultry litter (Hadjipanayiotou 1984; Hadjipanayiotou et al 1993). Furthermore, silage made from poultry litter, olive cake and wheat bran (45:45:10 w/w) was used without any deleterious effect as partial replacement for concentrates in diets of sheep in Tunisia (Kayouli et al 1993).

This paper presents results from research conducted to study fermentation characteristics and changes of nutritional components in ensiled by-products and how different levels of urea solution may affect the nutritional value of ensiled olive cake.

Poultry litter collected from a commercial broiler house, bedded with chopped cereal straw was used. The poultry litter was screened using a 20 mm metal grid to remove caked material. The screened poultry litter was weighed and spread over the other by-product already being in the mixer. The ingredients were thoroughly mixed. During mixing, water was added when needed to raise the moisture content to approximately 500 g/kg. Four laboratory silos and two original mixture samples were prepared from each silage. The silos were prepared by packing the thoroughly mixed material into double polyethylene bags. The bags were sealed after expelling the air above the packed mixture. The sealed bags were then placed in a 200 litre plastic barrel and covered with smooth clay soil. The bags were opened after a fermentation of 60 days. The aroma and colour of the silages were assessed by three persons using a scale of 1 to 4 (1=poor, 2= medium, 3=good and 4=very good).

Three mature, dry, Damascus goats, weighing on average 70 kg, and fitted with a permanent rumen cannula were used to measure the rumen degradability of olive cake, tomato pulp and poultry litter. The animals were kept in individual pens with concrete floors bedded with wood shavings. They were fed to maintenance a diet composed of concentrate (160 g N x 6.25/kg DM) and barley straw (0.7:0.3 ratio). The three by-products were incubated (2, 5, 8, 24, 48, 72 h) in nylon bags (3 bags/incubation interval) in the rumen of the animals as outlined by Hadjipanayiotou et al (1988). Samples were analyzed for DM and N before and after incubation. The mean of the three bags per incubation interval was used for calculations. Processing of samples after withdrawal of bags from the rumen was as outlined by Hadjipanayiotou et al (1988). Loss of DM and N at various incubation intervals was fitted to the non-linear equation [(Orskov and McDonald, 1979), P=1+b(1-e^-ct)], where ±P± is the amount degraded at time ±t±, ±a± is the rapidly degradable fraction, ±b±' is the potential degradability at infinite time and ±c± is the fractional rate constant at which the fraction ±b± will degrade per hour. Data collected (a, b, c and P) were analyzed by one way analysis of variance.

The proximate constituents and in vitro digestible organic matter in the dry matter were determined on dried (55 °C) and ground (1 mm) original and fermented samples by the following methods: total nitrogen (AOAC 1975); free ammonia by distillation using NaOH and titration of the distillate. Dry matter of all materials was determined by drying two approximately 200 g samples at 105 C in an air-forced oven for 48 h. In vitro digestibility of organic matter in the dry matter was determined by the procedure described by Tilley and Terry (1963) as modified by O'Shea and Wilson (1965). Ruminal fluid inoculum was obtained from three rumen-fistulated ewes given lucerne hay ad libitum.

Water extracts of the original and fermented materials were prepared by homogenizing 25 g of wet material with 100 ml water in a blender at full speed for 4 min. The contents were filtered through two layers of cheese-cloth and the filtrate was used to measure the pH. Lactic acid was determined in the extract by the method of MAFF (1973). The extract for acetic, propionic and butyric acid determination was prepared by mixing 25 g of the wet original and/or fermented sample with 50 ml of 0.05-N H₂SO₄; the mixture was allowed to stand in a freezer (4 °C) for seven days and shaken once daily. At the end of the 7th day the mixture was strained through two layers of fine muslin. One ml of pivalate solution (40 g/l) was added to 10 ml of the filtrate and mixed thoroughly in a vortex mixer. To 4 ml of this mixture one ml of H₃PO₄ solution (1 mmol/ml) was added, and the mixture centrifuged at 2000 rpm for 10 min. The supernatant was used for acetic, propionic and butyric acid determination in a Varian Gas Chromatograph 3300 fitted with flame ionization detector. The glass column (180 cm length and 1.4 mm internal diameter) was packed with GP 10% SP-1000, 1% H₃PO₄ and 100/120 chromosorb W-17W.

Tomato pulp, a mixture of seeds and skins, collected from a processing plant extracting tomato juice, was used. It was ensiled either alone, or in combination with poultry litter (ratios of tomato pulp to poultry litter were: (1) 1:0, (2) 10:1, (3) 7:1, (4) 4:1) and/or chopped straw (ratios of tomato pulp to straw were: (5) 10:1, (6) 15:1).

Olive cake, the residue obtained at the mill by pressing or centrifuging the oil contained in the whole olive, was ensiled either alone or with other ingredients (Poultry litter, ground maize grain, molasses). The proportions of the ingredients in the various formulae were: (1) Olive cake alone, (2) 95 Olive cake : 5 molasses, (3) 65 Olive cake : 35 poultry litter, (4) 62 Olive cake : 33 poultry litter : 5 molasses, (5) 62 Olive cake : 33 poultry litter : 5 maize grain, (6) 58 Olive cake : 32 poultry litter : 5 maize grain : 5 molasses, (7) 58 Olive cake : 32 poultry litter : 10 maize grain, (8) 52 Olive cake : 28 poultry litter : 20 maize grain. Water was added to raise the moisture content of the original mixture to 500 g per kg.

Untreated olive cake, and olive cake treated with 30, 50 or 70% (w/v) of urea solution at the rate of 100 ml per kg dry matter were ensiled as above for a period of 60 days.

The chemical composition of the various ingredients is in Table 1. The content of N x 6.25 and the digestibility value of poultry litter used in the present study were higher than for previously reported values (Hadjipanayiotou 1982). This was most likely due to the higher ratio of bedding to wasted feed/excreta/ feathers, and/or the type of bedding used (wood shaving vs chopped cereal straw); the high digestibility value can be explained also by the low crude fibre content.

In line with NRC (1989), tomato pulp was a good source of N x 6.25 and had a moderate energy density (about 8.7 MJ ME/ kg dry matter, % digestible dry matter x 0.15) and compared favourably with alfalfa hay (sun-cured, early to full bloom). Olive cake is a material of poor nutritional value, however, its ensiling with poultry litter, tomato pulp, some other by-products or conventional feedstuffs may give a silage mixture of moderate nutritional worth.

The composition of the initial mixtures was closely related to the composition of the basic ingredients. Addition of poultry litter at time of ensiling resulted in a significant increase in nitrogen content and pH values of all mixtures. Furthermore, incorporation of poultry litter in the mixtures containing tomato pulp decreased their digestibility value.

Table 1: Composition (g/kg) of poultry litter, straw, tomato pulp and crude olive cake and digestible organic matter in the dry matter

	Poultry		Tomato	Olive
	litter	Straw	pulp	cake

Dry matter (DM)	898	970	147	470
Dry matter basis
N x 6.25	296	51	181	48
Crude fibre	124	343	322	443
Ether extract	32	25	106	104
Ash	112	62	45	13
Neutral detergent
fibre	327	783	673	691
Acid detergent
fibre	199	833	412	551
Acid detergent
lignin	77	89	168	278
In vitro
digestibility	548	485	579	114

Table 2: Chemical composition (g/kg), in vitro D and pH values of different mixtures at ensiling (In this and subsequent tables PL=poultry litter; Str=straw; Mol=molasses, TP=tomato pulp; OC=crude olive cake; Mz=maize grain; C2=acetic; C3=propionic; C4=butyric; Lac=lactic acid)

	Dry	N x 6.25
	matt		Digestibilitiy	pH	C2	C3	Lactic

Trial 1:				Dry matter basis
TP	207	216	602	4.2	9	-	11
10TP/1PL)	255	233	564	5.5	7	-	8
7TP/1PL)	273	242	546	5.6	7	-	8
4TP/1PL	307	288	543	5.9	6	-	7
10TP/1str)	249	154	556	4.4	8	-	8
15TP/1str)	230	187	555	4.3	8	-	9

Trial 2:
OC	448	75	133	4.8	3	1	1
95OC/5Mol	446	64	174	4.9	1	1	1
65OC/35PL)	516	180	374	5.9	2	1	2
62OC/33PL/5Mol	514	138	417	6.0	1	1	4
62OC/33PL/5Mz	496	207	417	6.0	1	1	4
58OC/32PL/
5Mz/5Mol	522	137	430	6.0	2	1	4
52OC/32PL/10Mz	521	146	421	6.0	2	1	4
52OC/28PL/20Mz	528	130	488	5.9	2	1	4

Ensilingdigestibility values compared to non-fermented samples. This can be ascribed to the fermentation losses from the readily fermentable components for the production of fatty acids, and it is in line with the findings of Hadjipanayiotou (1982) and Harmon et al (1975). Comparison within original mixture samples (trial 3) showed an improvement of the in vitro digestibility value with the addition of a urea solution (14.4 vs 19.0%); the digestibility values were greater with the 7% urea (22.2%) than with the 3% (18.0%) or 5% (18.5%) urea.

There was no mould in any of the samples of silage. With the exception of silage 1 that rated ±good± for colour and aroma, all other silages of trial 1 had ±very good± aroma and colour. All silages of trial 2 had also very good aroma and colour. It has been reported by MaCaskey and Anthony (1975 cited by Roothaert and Matthewman 1992) that a pH value below 5 would kill Salmonella and other pathogens. This was the case in all fermented mixtures of trial 2, and some fermented mixtures of trials 1 and 3. The high pH value of olive cake silages treated with 5 and 7% urea can be explained by the conversion of urea to ammonia.

Table 3: Chemical composition (g/kg), in vitro digestibility and pH values of different fermented mixtures

	Dry	N x 6.25	Digest	pH	C2	C3	Lac

Trial 1:				Dry matter basis
TP	172	242	494	5.0	79	3	10
10TP/1PL	212	275	514	5.3	71	1	21
7TP/1PL	240	291	494	5.3	62	1	27
4TP/1PL	271	309	486	5.3	50	1	35
10TP/1str	213	190	486	5.0	76	4	6
15TP/1str	195	200	490	4.9	90	4	7
SE	±3.1	±4.3	±8.1	±.02	±2.5	±.4	±.1
Trial 2:
OC	482	70	112	4.6	3	1	3
95OC/5Mol	483	82	143	4.6	2	1	2
65OC/35PL	495	171	327	4.5	21	2	32
62OC/33PL/5Mol	492	163	343	4.5	15	1	33
62OC/33PL/5Mz	475	169	372	4.7	21	2	35
58OC/32PL/5CG/
5Mol	491	151	372	4.7	16	1	32
58OC/32PL/10Mz	502	162	390	4.7	17	2	34
52OC/28PL/20Mz	514	146	459	4.8	18	2	36
SE	±2.2	±2.7	±16	±.04	±.9	±.2	±.1

Taking into consideration the pH value, aroma and colour and the concentration of lactic, acetic and propionic acids in the silage in trial 2, it may be stated that good quality silage can be made from plain olive cake, and that addition of poultry litter, molasses or ground maize grain alone or in combination, will not improve further the digestibility of the silage, but will result in a nutritionally more balanced mixture.

Table 4: Chemical composition (g/kg), in vitro digestibility and pH values of different mixtures at ensiling (Trial 3)

		Dry Matter Basis
		Dry	N x	NH₃	Digest-	pH	C2	C3	C4	Lac
		matt	6.25		ibility

OC		466	57	-	144	5.0	32	-	0.7	0.2
OC+3%	urea	472	169	-	180	5.2	15	-	Nil	0.3
OC+5%	urea	471	187	-	185	5.0	32	-	0.1	0.1
OC+7%	urea	478	261	2.1	222	5.1	21	-	Nil	0.1

Spraying of olive cake with a urea solution improved its digestibility compared to the non-sprayed control; ensiling of urea-treated olive cake did not increase further the digestibility in vitro. This may be due to the fact that ammonia is a weaker alkali than NaOH which was effective in upgrading the nutritional value of olive cake in the studies of Nefzaoui et al (1983). The ammonia smell was very weak compared to that of straw treated with the same amount of urea; the low levels of free ammonia and the fact that almost all urea-N applied on olive cake was retained on it, may be due to the fact that there is not any urease present in olive cake to convert urea to ammonia; the possibility of using traces of soybean meal flour at ensiling to provide urease may be worth further study.

Table 5: Chemical composition (g/kg), in vitro digestibility and pH alues of different fermented mixtures (Trial 3)

	Dry	N x	NH₃	Digest	pH	C2	C3	Lac
	matter	6.25

OC	465	66	-	135	5.0	39	3	0.2
OC+3%urea	480	169	-	157	5.0	46	2	0.6
OC+5%urea	474	201	32	152	7.8	48	1	0.7
OC+7%urea	474	253	24	175	6.9	41	-	0.4
SE	±3.7	±7.2	±2.9	±5.1	±.23	±2.6	±.5	±.07

The data for effective degradability of dry matter and N x 6.25 of poultry litter, tomato pulp and olive cake are in Table 6. Values for degradability of N x 6.25 of olive cake are not presented in Table 6, because these were negative at many incubation intervals, possibly due to adhesion of large numbers of microbes resulting in severe contamination of the sample in the bag. Effective DM degradability values (at fractional outflow of 5%) of tomato pulp and poultry litter (Table 6) were very close to the digestibility values determined in vitro (Table 1). On the other hand, there were differences between the values for olive cake.

Table 6: Parameters for nylon bag degradabilities of dry matter and N x 6.25 of poultry litter, tomato pulp and olive cake

Item	Constants	PL	TP	OC

Dry matter	a	35.3±1.99	32.5±1.15	2.1±1.41
	b	47.0±2.26	40.4±2.61	20.9±2.98
	c	4.9±0.43	9.04±1.25	2.69±0.99
	p#	59.2±0.44	58.4±0.36	8.7±0.53
	p##	54.3±1.08	53.8±0.74	6.8±0.32

N x 6.25	a	79.3±1.0	50.2±2.05	ND
	b	18.4±0.9	48.3±1.10	ND
	c	1.38±0.11	0.8±0.13	ND
	p#	85.8±2.25	57.5±1.50	ND
	p##	86.4±3.73	55.4±1.01	ND
----------	----------	--------------	--------------	----------

ND not determined;
a,b and c are the constants of the exponential equation
[P=a+b(1-e^-ct)], representing the rapidly soluble fraction, the
fraction which will be degraded in time, and the rate at which
the ±b± fraction is degraded (Orskov and McDonald 1979),
respectively.

It is concluded that the ensiling technique can be safely used for extended storage of olive cake, and that mixing of olive cake with other by-products at ensiling not only gives a more balanced array of nutrients but it also results in better silage characteristics.

The author is grateful to A Photiou, M Karavia, M Theodoridou and the staff of the central chemistry laboratory for skilled technical assistance.

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