Caged-layer waste as a nitrogen source in crop-residue utilisation

S. B. Kayongo, M M Wanyoike, P N Nyagah, T E Maitho and P N Mbugua

Department of Animal Production
Faculty of Veterinary Medicine
University of Nairobi
PO Box 29053, Nairobi, Kenya

ABSTRACT

Poultry litter has a crude-protein content of about 22-25% and has been successfully used as a component of ruminant feeds. However, poultry waste is a potential carrier of pathogenic microorganisms and must be treated to reduce the risk of transmitting diseases. This study assessed the effect of sun-drying, ensiling, deep-stacking and fumigating with formaldehyde gas on the nutritional value of caged-layer waste (CLW). Deep-stacking resulted in a higher (P<0.01) ash content and undesirable odour, but also in a higher (P<0.01) dry-matter degradability (DMD) than the other treatment methods. Duration of sun-drying or deep-stacking or the number of times the CLW was fumigated did not affect (P>0.05) DMD in the rumen. However, ensiling CLW for 42 days resulted in a higher (P<0.01) DMD than ensiling for 21 days and also reduced odour.

In another study, CLW was ensiled in 21-litre plastic silos for 21 or 42 days, at 0, 20 or 40% (DM basis) rate of inclusion with crop residues having low crude-protein levels (maize stover, maize cobs or wheat straw). Fermentation (as indicated by pH) approached optimum (P<0.01) at 40% rate of CLW inclusion and 42 days of ensiling. Crude-protein, ash and in vitro dry-matter digestibility increased with level of CLW in the silage mixtures but NDF decreased (P<0.01). Ensiling fibrous crop residues with caged-layer waste could provide a means of more efficiently utilising caged-layer wastes and crop residues as livestock feed.

RESUME

Utilisation des déjections de pondeuses élevées en batteries comme source de complément protéique des résidus de récolte

Avec une teneur en protéines brutes d'environ 22 à 25%, la litière de volaille est incorporée avec succès dans l'alimentation des ruminants. Cependant, étant donné qu'elles peuvent transmettre des microbes, les déjections des volailles doivent être traitées pour réduire les risques de maladies. Une étude a été effectuée en vue d'évaluer l'effet du séchage solaire, de l'ensilage, de l'empilage et de la fumigation au formol sur la valeur nutritive des déjections de volailles. Par rapport aux autres méthodes, l'empilage, qui s'accompagnait d'odeurs désagréables, se traduisait par une plus forte teneur en matières minérales et un taux de dégradation de la matière sèche plus élevé (P<0,01). Ni la durée du séchage à l'air et de l'empilage, ni le nombre de fumigations n'avaient d'effet (P>0,05) sur la digestibilité de la matière sèche dans le rumen. Cependant un ensilage de 42 jours permettait de réduire les mauvaises odeurs et se traduisait en outre par une digestibilité de la matière sèche plus élevée (P<0,01) qu'un ensilage de 21 Jours.

Dans une autre étude effectuée immédiatement après, des déjections de pondeuses en batteries ont été ensilées pendant 21 ou 42 jours dans des silos en plastique (environ 21 litres). Elles avaient été incorporées à 0, 20 ou 40% (sur la base de la matière sèche) dans des résidus de récolte pauvres en protéines brutes (paille de maïs, épis égrenés de mais ou paille de blé). La fermentation (mesurée par le pH) était maximum (P<0,01) au taux de 40% et avec l'ensilage de 42 jours. Enfin, la teneur en protéines brutes, le taux de matières minérales et la digestibilité in vitro de la matière sèche augmentaient alors que la teneur en parois cellulaires diminuaient (P<0,01) avec la proportion de déjections. L'ensilage des résidus de récolte riches en cellulose avec des déjections de pondeuses en batteries peut donc permettre d'utiliser l'un et l'autre produits de manière plus rationnelle.

INTRODUCTION

In Kenya, crop farming produces a wide range of crop residues, mainly maize cobs, maize, sorghum and millet stovers and wheat, barley and rice straws. Other important crop residues are produced by the sugar industry and from horticultural crops. An estimated 7.2 million tonnes of highly lignified arable farm products are produced annually (Said and Wanyoike, 1987). However, it is difficult to assess the amounts of crop residues fed to livestock as there are great variations with season and individual farm requirements.

Most available crop residues have low protein and high fibre contents, factors that lead to their poor utilisation by livestock (Said and Wanyoike, 1987). Utilisation of the energy component of such materials by ruminants is highly dependent on the efficiency of fermentative activity in the rumen (Mehrez et al, 1977) which depends, in turn, on adequate supplies of nitrogen in the rumen. Positive responses on intake and liveweight gain have been recorded when a nitrogen source has been included in a diet based on crop residues (Alayu, 1987). In Kenya, most studies on crop residues have been on evaluating chemical treatment methods such as the use of alkali and/or urea to improve utilisation (Kevelenge et al, 1983; Alayu, 1987; Said and Wanyoike, 1987). However, the applicability of results from such work has been limited by the high cost of chemicals and by farmers' lack of knowledge. The need has thus arisen to find alternative, more practical, ways to improve the nutritive value of crop residues.

Caged-layer waste (CLW) is reported to contain between 22.3 and 25% crude protein (Kayongo and Muinga, 1985; Nambi, 1987). Between 40 and 50% is true protein and the rest non-protein nitrogen (Nambi, 1987). However, feeding unprocessed CLW can pose potential health hazards, both to the livestock consuming the feed and to people eating products (meat and milk) from such animals (Shah and Müller, 1983). Ensiling is an inexpensive biological method of processing poultry litter for incorporation into rations (Caswell et al, 1977; Shah and Müller, 1983). It has also been reported that ensiling broiler litter with corn forage or wheat straw improved the nutritional value of the crop residues compared to ensiling the crop residues by themselves (Caswell et al, 1977; Daniels et al, 1983). This study therefore examined the effect of processing methods on the composition and degradability of CLW. The effect of ensiling CLW (as a nitrogen source) with crop residues on the chemical composition and degradability of the silage was also investigated.

MATERIALS AND METHODS

Experiment 1. Processing methods

Caged-layer waste was collected from laying Shavers chickens, aged 50 weeks and housed in battery cages. A polythene sheet was spread below the cages and the droppings, which included excrete, feathers, broken eggs and spilled feed, were collected after three days. The waste was processed by one of four methods, all applicable at farm level in Kenya:

Sun-drying. Caged-layer waste was spread on polythene sheets in 1-2-cm thick layers and raked thoroughly twice a day. Drying lasted four or eight days at an average temperature of 25.74°C and radiation intensity of 20.37 MJ.

Ensiling. Caged-layer waste was packed into plastic silos with a capacity of 0.021 m³ (21 litres) and left for either 21 or 42 days. Samples were taken at ensiling and after opening the silos.

Deep-stacking. Deep-stacking was achieved by heaping approximately 1000 kg of caged-layer waste on a concrete floor under direct sunshine. The stack was then covered with a polythene sheet and sampled after 21 or 42 days by taking composite samples from the entire stack.

Fumigation. Caged-layer waste was spread on perforated trays in layers 0.5-1 cm thick and sun-dried for two days. The trays were then placed in an air-tight metal chamber with a capacity of 0.81 m³. The chamber was fumigated using a 1:2 mixture of potassium permanganate and 40% formalin in a glass jar: the amount of formalin used was 1.85 ml per chamber. Fumigation was carried out four or eight times: the CLW was turned by hand after each fumigation.

All samples were dried in an oven at 60°C for 48 hours, ground in a Wiley mill a 2-mm screen and stored in air-tight bottles.

In sacco dry-matter degradability studies were carried out using five fistulated Somali Blackhead wether sheep (15-18 months old; average weight 32.4 kg.) The sheep were fed Rhodes grass (Chloris gayana) hay and supplemented with a commercial concentrate at a rate of 0.3 kg/animal per day. The animals were dewormed with Valbazen 10% (Kenya Swizz Chemical Company, Nairobi, Kenya) at a rate of 1 ml per 10 kg body weight one week before the start of the study.

Samples (5 g) of each feed were weighed into nylon bags (15 x 7 cm: pore size of 35 m m). The bags were attached to nylon cords and incubated inside the rumens of the sheep for 6, 12, 24, 48 or 72 hours. After incubation the bags were removed, washed thoroughly with tap water, dried at 70°C in an oven for 24 hours and weighed to calculate dry-matter losses (Ørskov and McDonald, 1979). The experimental layout was a 4 x 2 x 5 factorial arrangement in a completely randomised design, with four treatment methods at two levels each and five durations of incubation in the rumen. Unprocessed CLW was used as the control giving a total of nine test feeds.

Experiment 2. Effect of ensiling crop residues with graded levels of caged-layer waste

Maize stover and cobs and wheat straw were cut into 2.5-5-cm lengths; water was added at a ratio of 1:1 to increase moisture content. Freshly collected caged-layer waste was mixed with the crop residues at a rate of 20 or 40% (dry-matter basis): no CLW was added to the control materials. Molasses was added to all ensilages at a rate of 5%. The ensilage materials were thoroughly mixed by hand and packed in 21-litre plastic silos in triplicate. The silos were opened after 21 or 42 days. The top 2.5 cm of the silage from each silo was discarded. The silages were observed for colour, odour and any mould growth.

Proximate composition of crop residues, molasses, CLW and silages before and after fermentation was determined using standard AOAC (1984) procedures. Detergent fibres were analysed by the methods of Van Soest (1963) and Van Soest and Wine (1967). In vitro dry-matter and organic-matter digestibilities of the crop residues, CLW and silages were determined by the methods of Tilley and Terry (1963). Water extracts of the silages were prepared by homogenising 25 g of wet silage with 100 ml distilled water in a blender for two minutes. The homogenate was filtered through four layers of cheese cloth and its pH measured

The rest of the silages were dried at 60°C for 48 hours, milled through a 2-mm sieve and stored in air-fight jars. Samples (5 g) of each milled silage were weighed into nylon bags and incubated for 12, 24, 36, 48 or 72 hours in the rumens of the same sheep used in Experiment 1. A completely randomised design with a factorial arrangement of 3 x 3 x 3 x 5 (three crop residues, at three levels of CLW, three durations of ensiling and five incubation times) was used.

Calculations

In both experiments, was estimated using the model developed by Ørskov and McDonald (1979):

p = a + b(1 - e^-ct)

where:

p = actual degradation after time t
a = readily degradable fraction (%)
b = potential degradable fraction (%)
c = rate constant for the degradation of b
t = incubation time (hours).

The constants a, b, and c were derived using EUREKA, an iterative computer programme (Borland International Inc). The data obtained were subjected to analysis of variance using Harvey's Least-Squares analysis. The differences between treatment means were tested with orthogonal contrasts.

RESULTS AND DISCUSSION

Experiment 1

Chemical composition of unprocessed and processed CLW

The proximate compositions of unprocessed, sun-dried, ensiled, deep-stacked and fumigated CLW are shown in Table 1. Dry-matter (DM) content increased with increasing duration of sun-drying and deep-stacking as has also been reported by Fiano et al (1984) when CLW was sun-dried for 30 days. Fumigated CLW also had a higher DM content than fresh CLW. However, ensiling did not change the DM content of CLW. Crude-protein (CP) content had declined sharply after sun-drying for four days, but thereafter the decrease was negligible; this result is also in agreement with the study by Fiano et al (1984). The loss in CP was attributed to the breakdown of uric acid (Caswell et al, 1975) which constitutes 40 to 50% of total nitrogen in CLW (Nambi, 1987). Direct sunlight could have caused volatisation of the uric acid (Fiano et al, 1984); Caswell et al (1975) showed that dry-heat processing of broiler litter lowered the uric acid nitrogen as well as ammonia nitrogen. Other treatment methods did not affect the CP values significantly.

Deep-stacking increased the ash content of CLW suggesting that CLW underwent a composting process in which the organic matter might have been converted into soluble materials (Müller, 1982). This increase in ash content might reduce the digestible energy of CLW and hence its nutritional value (Müller, 1982). The other methods had no effect on ash content of CLW; this result is in agreement with observations by Fiano et al (1984) from air-drying, autoclaving and oven-drying of CLW.

Table 1. Chemical composition of unprocessed and processed caged-layer waste

Processing method		Proximate component (%)
		Dry matter	Ash	Crude
Unprocessed		31.02	20.50	21.80
Sun-drying
	4 days	81.44	21.57	13.13
	8 days	90.12	20.22	12.76
Ensiling
	21 days	28.88	23.92	17.29
	42 days	29.41	23.80	18.72
Deep-stacking
	21 days	54.17	33.56	16.38
	42 days	78.10	35.45	17.20
Fumigation
	4 times	77.32	21.04	17.97
	8 times	76.52	20.98	16.55

Degradation characteristics of unprocessed and processed CLW

Dry-matter degradabilities (DMD) of unprocessed and processed CLW are shown in Tables 2 and 3. Deep-stacked CLW had a higher DMD (P<0.01) than CLW processed by the other methods, whose DMD were similar (P>0.05). However, the deep-stacked CLW had an offensive odour. DMD increased (P<0.01) with incubation time for all methods of processing, as has also been reported by Alayu (1987).

Sun-drying for four or eight days, deep-stacking for 21 or 42 days or fumigation four or eight times did not affect DMD of CLW within method (P>0.05). However, ensiling for 42 days gave superior (P<0.01) DMD than ensiling for 21 days. This result agrees the finding of Daniels et al (1983) who reported that ensiling broiler litter for 42 days gave better quality silage.

Experiment 2

Chemical composition of crop residues ensiled with CLW

Table 4 shows the chemical composition of the crop residues and molasses used for ensiling with CLW. All the three crop residues had low crude-protein and high crude-fibre and detergent fibre contents, in total agreement with reports by Kevelenge et al (1983), Alayu (1987) and Tuah and Ørskov (1989). After ensiling, all silages that had CLW as an additive had a pleasant aroma, a gold-brown colour and no mould growth. However, the control silages only had a weak characteristic silage smell. Similar observations have been made on poultry litter ensiled alone or with barley straw, a mixture of weeds and grapefruit peels (Hadjipanayotou, 1982).

Table 2. Least-squares means of the effect of method, within method and time on dry-matter degradability of unprocessed or processed caged-layer waste

Independent variable		Dry-matter digestibility (%)
Processing methods
Unprocessed		41.99
Son-drying		41.67
Ensiling		43.85
Deep-stacking		53.42
Fumigation		43.63
SE		0.60
Level within method
Sun-drying
	4 days	41.22
	8 days	42.13
Ensiling
	21 days	40.85
	42 days	46.86
Deep-stacking
	21 days	53.46
	42 days	53.37
Fumigation
	4 times	44.41
	8 times	42.85
SE		0.85
Duration of incubation
6 hours		27.69
12 hours		33.67
24 hours		45.27
48 hours		54.98
72 hours		62.96
SE		0.64

Table 3. Pitted dry-matter degradation constants for unprocessed and processed caged-layer waste incubation in nylon bags in the rumen of sheep

Method of processing		Degradation constants a
		a	b	c
Unprocessed		20.4	49.9	0.021
Sun-drying
	4 days	20.9	51.9	0.019
	8 days	13.6	51.3	0.034
Ensiling
	21 days	15.6	43.8	0.036
	42 days	22.1	66.5	0.017
Deep-stacking
	21 days	24.5	53.0	0.026
	42 days	29.4	45.3	0.030
Fumigation
	4 times	18.9	57.6	0.022
	8 times	19.2	39.3	0.040

^a From the model p = a + b (1 - e^-ct)

p = actual degradation after time t
a = readily degradable fraction (%)
b = potential degradable fraction (%)
c = rate constant for the degradation of b
t = incubation time (hours)

The pH values were not affected (P>0.05) by type of crop residue (Table 5). However, maize stover and wheat straw silages had higher CP and ash and lower neutral detergent fibre (NDF) (P<0.01) than silage based on maize cobs. These changes could be attributed to the inclusion of CLW in the mixtures. As the level of CLW was increased from 0 to 40% there was a significant increase in pH, CP, ash and in vitro dry-matter digestibility (IVDMD) of the resultant silage whereas NDF values decreased. Similar findings have been reported by Daniels et al (1983) and Hadjipanayotou (1984). Ensiling for either 21 or 42 days had no effect on ash and NDF content of the silages (P>0.05) but significantly decreased pH (P<0.01) suggesting that desirable fermentation had taken place (Daniels et al, 1983).

Degradability of crop residues silages

Wheat straw silage had a higher degradability (P<0.01) value than maize stover and maize cob silages (Table 6), probably because of higher readily soluble cell contents (Tuah and Ørskov, 1989). Tables 6 and 7 show that increasing the level of CLW in the ensilage significantly (P<0.01) increased the degradability, probably because of increased nitrogen content (Alayu, 1987). There was an increase (P<0.01) in degradability when the duration of ensiling was increased from 21 to 42 days suggesting that a longer period was desirable to facilitate microbial activity on the ensiled crop residues (Daniels et al, 1983). Alayu (1987) reported that extending treatment time for wheat straw from 14 to 28 days improved the DM degradability. The increase in degradability of the silages with longer duration of ensiling could be attributed to the increased degradability of CLW observed in Experiment 1 when CLW was ensiled for up to 42 days. The longer the silages were incubated in the rumen the higher was the degradability, in agreement with earlier studies on wheat straw treated with urea (Alayu, 1987).

Table 4. Chemical composition of maize stover, maize cobs, wheat straw, caged-layer waste and molasses used in Experiment 2

Component		(%)
		Maize stover	Wheat straw	Maize cobs	Caged-layer waste	Molasses
Dry matter		94.30	94.30	91.76	30.65	67.74
Crude protein		4.60	3.64	4.20	22.5	3.40
Ash		3.20	2.32	4.68	20.36	8.32
Crude fibre		45.70	47.86	48.61	6.69	0
Neutral detergent fibre		85.25	84.28	91.84	57.65	-
Acid detergent fibre		58.0	58.79	44.84	22.80	-
Lignin		8.40	7.33	14.96	6.12	-
Cellulose		49.60	51.46	29.88	16.68	-
Hemicellulose		26.75	25.49	47.0	34.85	-
Cell content		14.75	15.72	8.16	42.35	-
In vitro digestibility
	Dry matter	30.32	29.84	43.58	74.31	*
	Organic matter	29.32	32.19	42.70	74.40	*

^* Not assessed

Table 5. Least-squares means for chemical composition and in vitro digestibility of crop residues ensiled with caged-layer waste

Independent variable	pH	Crude protein (%)	Ash (%)	In vitro dry-matter digestibility (%)	Neutral detergent fibre (%)
Crop residues
Maize stover	4.36	9.31	10.89	60.79	69.67
Wheat straw	4.09	9.11	10.09	57.41	67.12
Maize cobs	4.39	7.62	6.76	59.89	77.08
Level of caged-layer waste
0%	4.39	5.39	6.34	53.57	80.07
20%	4.72	9.03	9.51	60.93	70.40
40%	4.93	11.63	12.71	63.60	63.40
Duration of ensiling
0 days	5.32	7.67	9.40	60.37	72.10
21 days	4.57	9.39	9.55	58.65	70.67
42 days	4.16	8.99	9.61	59.09	71.11
SE	0.03	0.13	0.24	0.33	0.43

Table 6. Least squares means for dry-matter degradability of crop residues ensiled with caged-layer waste

Independent variable	Dry-matter degradability (%)
Crop residue
Maize stover	39.16
Maize cobs	37.75
Wheat straw	41.03
SE	0.42
Level of caged-layer waste
0%	32.08
20%	39.83
40%	45.99
SE	0.42
Duration of ensiling
0 days	38.16
21 days	39.05
42 days	40.69
SE	0.42
Incubation time in the rumen
12 hours	22.09
24 hours	26.72
36 hours	35.65
48 hours	50.03
72 hours	57.59
SE	0.60

Table 7. Fitted dry-matter degradation constants for crop residues ensiled with caged-layer waste

Crop residue	Duration of ensiling (days)	Level of CLW (%)	Degradation constants a
			a	b	c
Maize stover	0	0	7.9	55.7	0.011
		20	13.1	78.3	0.011
		40	19.8	78.8	0.014
	21	0	13.9	62.8	0.010
		20	16.3	64.1	0.014
		40	19.4	67.1	0.017
	42	0	10.9	86.1	0.010
		20	15.6	72.9	0.023
		40	21.3	66.4	0.030
Maize cobs	0	0	11.1	45.9	0.009
		20	16.0	59.5	0.011
		40	18.5	62.8	0.013
	21	0	12.2	48.5	0.011
		20	12.5	58.5	0.017
		40	19.3	64.9	0.021
	42	0	13.5	53.9	0.011
		20	13.4	52.4	0.018
		40	14.5	69.6	0.024
Wheat straw	0	0	12 5	52.9	0.013
		20	15.6	67.2	0.013
		40	15.9	76.2	0.020
	21	0	13.3	55.9	0.013
		20	14.1	52.7	0.018
		40	16.4	75.2	0.019
	42	0	10.2	64.0	0.013
		20	17.5	71.3	0.019
		40	17.9	72.0	0.023

^a From the model p = a + b(1 - e^-ct)

p = actual degradation after time t
a = readily degradable fraction (%)
b = potential degradable fraction (%)
c = rate constant for the degradation of b
t = incubation time (hours)

CONCLUSIONS

The study showed that processing CLW by deep-stacking gave best results with respect to DM degradability. However, the steep increase in the ash content was indicative of composting, which might reduce the nutrient utilisation of deep-stacked CLW. Therefore, ensiling for 42 days would be preferred for odour control of the processed product. Ensiling crop residues with CLW as the additive at an inclusion rate of 40% and ensiling for 42 days was considered to be beneficial in improving the nutritional value of the crop residues. Investigations into the performance of growing sheep fed such silage are underway at the University of Nairobi.

ACKNOWLEDGEMENT

This study was funded by the Norwegian Agency for International Development (NORAD, Project KEN 046) to which the authors are grateful.

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