Rice straw in complete pelleted diets for sheep

M. N. Shehata and A. M. Nour
Department of Animal Production
Faculty of Agriculture, Alexandria University, Egypt

Summary
Introduction
Materials and methods
Results and discussion
References

Summary

Shortages of feed and increasing feed costs at a time of increasing demand for more animal products have stimulated interest in ways of making effective use of agro-industrial byproducts in the diets of ruminants in Egypt.

Chopped rice straw was mixed with the governmental concentrate mixture in a ratio of c. 1:1 and pelleted with or without the addition of 3% urea, 3% urea and 6% molasses, and 2% mineral mixture, with or without previous treatment with 5% NaOH or 4% NaOH plus 2% Ca(OH)2. The sodium hydroxide or sodium hydroxide and calcium hydroxide were sprayed on to the chopped rice straw before grinding and pelleting.

The experimental complete pelleted diets were fed to four mature Rahmany sheep in several digestibility trials and compared with the governmental concentrate mixture alone. The results showed that the voluntary feed intake was significantly increased by including rice straw in the pellets. The values were 1.44 kg/day and 1.73-2.18 kg/day for the concentrate mixture alone and the pelleted diets respectively.

The digestibility coefficients (%) of DM and OM and the feed value (TDN %) were similar when the concentrate mixture was fed alone (diet I) or mixed (1:1) with rice straw (diet II) without any addition. The addition of urea (diet III) compared with no addition (mix II) had no significant effect on OM, EE and NFE digestibilities or the feed value (61.5 and 60.6% TDN respectively); however, the digestible crude protein was significantly increased (12.2 and 9% respectively). The addition of 6% molasses and 2% minerals and vitamins (diet IV) significantly increased the digestibilities of DM, OM, CP, CF and NFE, and also raised the feed value (TDN %) related to diets I, II and III respectively. NaOH (5%) treated straw in mix V did not increase the digestibilities or the feed value relative to the untreated rice straw (diet IV). Treatment of rice straw with 4% NaOH and 2% Ca(OH)₂ (diet VI) had a negative response on the digestibilities and feed value compared to diet II.

The cost of one tonne of TDN was calculated as LE 104.2, 109.0, 111.7, 103.6, 114.4 and 129.7 for diets I, II, III, IV, V and VI respectively.

The present results suggest that the pelleting of untreated rice straw with the governmental concentrate mixture and additions of molasses, urea and minerals (diet IV) provides a suitable complete diet for use on large farms in Egypt.

Introduction

In Egypt, serious shortages of feed hinder improvements in animal production. However, there is an increasing demand for more animal products brought about by increased population growth and improved living standards.

The annual feed requirement of animals in Egypt is estimated to be about 7.56 million t of SV (starch value). There are two distinct feeding periods during the year - winter and summer. During the winter period, which covers 165 days from December to May, berseem is fed and this supplies 4.81 million t of SV (69.1% of that supplied by all feedstuffs). In this period, animals do not require more than 3.47 million t of SV. Consequently, there is a surplus of 1.34 million t from green berseem. During the summer period, which lasts 200 days, animals and poultry require 4.07 million t of SV. The summer feeding stuffs (green forages, straws and concentrates) provide 2.1 million t of SV (Gabra, 1984). Therefore, there is a deficiency of about 1.91 million t of SV. The above data show that there is an unbalanced distribution of nutrients over the year. The animals are overfed in winter and underfed in summer.

More effort should be made to increase the availability of feed in Egypt through the utilization of agro-industrial byproducts in ruminant diets. Cereal straw (about 11 million t, El-Saify et al, 1983) is the most widely available of all crop residues, but its value is limited by its inherently low digestibility (35-45%), its limited consumption by animals (less than 2% of the bodyweight) and its slow rate of passage (Jackson, 1978). The net result is a low intake with little or no surplus energy for growth, work or production. Protein supplements increase intake while alkali treatment of straw increases digestibility, and usually voluntary intake as well (Jackson, 1977). On small-scale farms, ensiling rice straw with urea (5%) is the best method of using rice straw (Nour, unpublished data). However, on large-scale farms (feedlots), grinding and pelleting of straw could be the best method of utilization. It is not yet known whether the separate effects of alkali treatment and grinding and pelleting are additive. It seems likely that the high temperature and pressure combination to which treated straw is subjected in the pelleting process enhances the effectiveness of alkali treatment. The industrial processing of straw into pelleted complete diets, containing 6080% straw, appears to have good prospects in Asia, where large numbers of milk animals are kept in or near cities and feed is transported from the surrounding countryside. Factories for this purpose have already been designed (Rexen and Vestergaard Thomsen, 1976).

The main objective of this research was to study the effect of different treatments of rice straw (with 5% NaOH or with 4% NaOH and 2% Ca(OH)₂) together with additions (urea-molasses and mineral mixture) on the feeding value and cost of a complete diet, containing 40-50% rice straw, for sheep.

Materials and methods

Rice straw bales were chopped through a J F machine (straw processor SP 2000). A portion of the chopped straw was sprayed with 5% NaOH (20% solution) as described by Jackson (1977). Another portion of the straw was sprayed with 4% NaOH and 2% Ca(OH)₂ in concentrated solution. The treated portions of rice straw were kept for 1 week.

Six pelleted diets were then prepared in the feed mill from components described in Table 1. Four mature Rahmany rams of about 45 kg liveweight were used to estimate coefficients of digestibility, nutritive value and nitrogen balance of these pelleted diets. The animals were kept in individual pens and fed ad libitum. Each trial consisted of a 21-day preliminary period followed by a 7-day collection of total faeces and urine.

Samples of feeds and faeces were analysed for proximate composition using the AOAC (1970) methods. Statistical analyses were made according to Snedecor (1956).

Results and discussion

The chemical composition of the tested diets is presented in Table 2. The diets (except the concentrated mixture, diet I) contained between 12 and 14% ash, 3.92 and 5.11% ether extract, 12.4 and 17.6% crude protein, 19.9 and 25.7% crude fibre and 41.5 and 45.8% nitrogen-free extract. The differences in crude protein between the tested diets are due to the effect of urea addition, while the differences in crude fibre are due to alkali treatments in diets V and VI.

Results for dry matter intake, digestibility coefficient and the feeding value of the diets are shown in Table 3. Diets I and II show the differences between the governmental concentrate mixture and the complete ration containing concentrate and rice straw in the ratio of 1:1. Rice straw increased the feed intake of animals from 1.44 to 2.31 kg/head/day respectively. A similar result was reported by White et al (1971). Addition of urea (diet III) or urea/molasses and minerals (diet IV) did not increase the feed intake to the level of diet II. On the other hand, the treatment of rice straw with alkali (diets V and VI) decreased the feed intake relative to the control diet (diet II).

Table 1. Composition of the complete pelleted diets containing rice straw.

	Diet No.
	I	II	III	IV	V	VI
Concentrate mixture*	100.0	50.0	50.0	50.0	50.0	50.0
Rice straw+	-	50.0	47.0	40.0	40.0	40.0
Urea			3.0	3. 0	3 0	3 0
Molasses	-	-	-	6.0	6.0	6.0
Minerals and vitamins	-	-	-	2.0	2.0	2.0

* The concentrate mixture contained 42% undecorticated cotton seed meal, 25.5% wheat bran, 5% rice bran, 22% maize, 2% molasses, 2% limestone, 1% sodium chloride, 0.1% Vit. A & D and 0.4% mineral mixture.

+ Rice straw in diet V was previously treated with 5% NaOH and in diet VI with 4.0% NaOH and 2.0% Ca(OH)₂.

Table 2. Chemical composition of the experimental pelleted diets.*

Diet No.	Dry matter (%)	% on DM basis
		CP	EE	Ash	CF	NFE
I Concentrate mixture	91.4	17.4	3.72	6.4	6.6	55.4
II Complete diets	92.3	12.4	4.99	14.0	25.7	42.9
III " "	92.6	15.7	5.09	12.1	21.6	45.6
IV " "	92.0	15.6	5.11	12.5	25.3	41.5
V " "	91.4	15.8	3.92	13.6	20.9	45.8
VI " "	86.9	17.6	4.83	14.8	19.9	43.0

* The chemical analysis of untreated rice straw was 93.0% DM and on % of DM basis the following: 3.93% crude protein, 2.04% ether extract, 16.5% ash, 43.4% crude fibre and 34.1% nitrogen free extract.

Table 3. Coefficients of digestibility and nutritive value of the pelleted diets.

		Complete diets*
		I	II	III	IV	V	VI
Feed intake (kg/day)		1.44	2.31	2.07	2.18	1.73	1.96
Digestibility coefficient %
	Dry matter	62.4+1.2	60.7+4.7	58.4+1.5	68.9+1.6	69.4+2.5	57.7+1.2
	Organic matter	65.1+1.0	63.6+4.1	63.2+1.4	71.8+1.5	71.9+2.4	61.8+1.4
	Crude protein	67.5+1.1	72.7+2.8	77.6+0.8	80.5+1.0	79.1+1.9	75.1+0.4
	Ether extract	79.9+1.6	94.1+1.8	94.1+1.4	94.6+1.9	93.2+1.4	88.7+3.1
	Crude fibre	41.1+2.3	54.2+2.7	49.2+3.1	66.5+2.6	61.0+2.9	42.9+3.1
	Nitrogen free extract	70.3+1.0	63.0+5.9	61.4+2.4	69.0+2.0	72.7+2.5	62.1+2.1
Nutritive value %
	Digestible crude protein	11.8+0.1	9.0+0.4	12.2+0.1	12.5+0.2	12.5+0.2	13.4+0.2
	Total digestible nutrients	64.3+0.9	60.6+3.4	61.5+1.1	68.7+1.5	66.6+2.1	58.1+1.0

*See table 1 for diet composition.

The digestibility coefficients for DM, OM and NFE and the feeding value (DCP % and TDN %) were slightly decreased by substituting rice straw for 50% of the concentrate mixture but the digestibilities of crude protein, ether extract and crude fibre were significantly increased in the complete diet containing 50% rice straw (Table 3). The complete diet contained about 12% crude protein, which is about optimum for maximum protein utilization in ruminants. The concentrate mixture contained more than 17% protein. Consequently, one could expect a higher digestibility of crude protein in the concentrate mixture than in the complete diet. On the other hand, the source of crude fibre in the concentrate mixture was mainly from cotton seed hulls in cottonseed cake. In previous work, Fahmy and El-Shazly (1979) found that the digestibility coefficients for cotton seed hulls were respectively 34.5, 41.8, 40.6, 44.4 and 38.8% for OM, CP, EE, NFE and crude fibre. On the other hand, Fahmy (1985) showed that the digestibility coefficients for rice straw were 63.5, 5.8, 59.3 and 75.2% for OM, EE, NFE and CF respectively. From these results it can be concluded that the digestibility of CF in rice straw is double that in cotton seed hulls and this may explain the higher CF digestibility in the complete diet containing rice straw. The addition of urea to the diet (diet III) did not improve digestibility or feed value expressed as TDN %. However, the addition of urea significantly increased the digestibility of crude protein relative to the unsupplemented diet (diet II). The addition of urea/molasses and minerals and vitamins to the complete diet (diet IV) significantly increased the digestibility of DM, OM, CP, CF and NFE and also the feed value of this diet.

The TDN value of rice straw (40%) was found to be much lower than that of the governmental concentrate mixture (64.3%). However, feed consumption, digestibility and feed value of the diets containing rice straw were not significantly different (Table 3). This means that the presence of rice straw in the diet improved the utilization of feed constituents. A similar result was obtained by Fahmy et al (1968) and Nour and El-Shazly (1980) with rice hulls. The addition of sand to a diet high in concentrates stimulated better utilization of the ration (Gooley and Burroughs, 1962). The relatively high silica in rice straw (in the present experiment) and rice hulls (Fahmy et al, 1968; Nour and El-Shazly, 1980) may have produced a similar effect.

Replacing 50% of the governmental concentrate mixture with rice straw, molasses, urea and minerals produced no significant differences in digestibility and nutritive value, though mean TDN % was higher in the concentrate mixture (diet I) than in the complete diets without molasses, urea, minerals and vitamins (diets II and III).

On the other hand, it was found that previous NaOH-treatment of rice straw (diet V) did not improve the digestibility or feed value relative to the complete diet containing untreated rice straw. Treatment of rice straw with 4% NaOH and 2% Ca(OH)₂ greatly decreased the digestibility of DM, OM, CF and NFE and the TDN % relative to the diets containing untreated rice straw alone or treated with NaOH (Table 3).

From the present results the cost of TDN % was calculated for each diet (Table 4). The cost of one tonne of TDN in the governmental concentrate mixture was about 104.2 LE. This cost was increased by substituting rice straw (diet II), rice straw and urea (diet III) or rice straw treated with alkali, urea and molasses (diets V and VI) for the concentrate. However, the cost decreased with diet IV. This clearly indicates the great potential of complete diets to help overcome the problem of feed shortage in Egypt by increasing the quantity of feeds without seriously affecting the quality. By applying these results, the amount of pelleted material could be increased from c. 1.5 million t to 3 million t.

Table 4. Cost (LE) of one tonne of pelleted feeds.

	Complete diets*
	I	II	III	IV	V	VI
Concentrate mixture	67	33.5	33.5	33.5	33.5	33.5
Rice straw	-	17.5	16.5	14.0	14.0	14.0
Urea	-	-	3.8	3.8	3.8	3.8
Molasses	-	-	-	0.9	0.9	0.9
Minerals and vitamins	-	-	-	4.0	4.0	4.0
Sodium hydroxide	-	-	-	-	5.0	4.0
Calcium hydroxide	-	-	-	-	-	0.1
Diet manufacture	-	15.0	15.0	15.0	15.0	15.0
Total cost (LE/t)	67.0	66.0	68.0	71.2	76.2	75.3
Feeding value TDN %)	64.3	60.6	61.5	68.7	66.6	58.1
Cost of one t TDN	104.2	109.0	111.7	103.6	114.4	129.7

*See Table 1 for diet composition.

The cost was calculated on the following basis (LE/t):

1. Concentrate mixture	67.0
2. Rice straw (chopped)	45.0
3. Urea	126.5
4. Molasses	15.0
5. Minerals & vitamins	200.0
6. Sodium hydroxide	250.0
7. Calcium hydroxide	15.0

References

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