Prediction of nutritive value of some crop residues and agro-industrial byproducts from their chemical analysis

Nd. Mbaye and Ch. Sall
Laboratoire National de l'Elevage et de Recherches Veterinaires
Institut Senegalais de Recherches Agricoles
(ISRA), Dakar-Hann, Senegal

Introduction
Objectives
Material and methods
Results
Conclusion
References

Introduction

Natural pastures and crop residues, together with agro-industrial byproducts, constitute the principal feed resource in Senegal. An inventory of byproducts was prepared in 1979 by Mongodin and Tascher and various aspects of their use have been discussed by Sall (1985), Mbaye (1982) and Sansoucy and Emery (1982).

Some results obtained in Senegal are summarised in this paper, although they are limited to results concerning groundnut and cotton seed hulls offered alone or in association with more concentrated byproducts such as groundnut cake, cotton seed cake, wheat, rice or maize bran, brewers' dried grain and molasses.

Objectives

Studies have been concerned with the chemical analysis, voluntary intake by sheep, dry matter digestibility (DMD) organic matter digestibility (OMD) and nitrogen (crude protein) digestibility (CPD) of byproducts.

The results have allowed us to establish preliminary equations relating intake and nutritive value of various feeds to their chemical analysis.

Material and methods

About 90 digestibility trials have been carried out of which 10 were on cattle. Standard methods were used: in vivo and in vitro (Tilley et Terry) digestibility; determination of crude fibre (Weende); total nitrogen and ash content.

The results were submitted to "step wise" regression analysis, permitting either simple linear or multiple equations to be derived.

Results

Feed value of groundnut hulls and cotton seed hulls offered alone (Table 1)

Groundnut hulls and cotton seed hulls are characterized by a high fibre content, averaging 540-550 g/kg DM. Cotton seed hulls were however, more digestible; DMD was found to be 40% when fed alone and 44% when fed with a mineral supplement.

Table 1. Feed value of groundnut hulls and cotton seed hulls offered alone to sheep.

No. of trials	Description	Intake (g/kg DM)			%		g/kg		FU	g/kgW0.75
		DM	CF	CP	DMD	OMD	DOM	DCP	Energy	DMI	DOMI
3	Groundnut hulls	966	547	115*	26	27	912	41	0.05	47	13
2	Cottonseed hulls	963	547	60	40	41	400	-	0.29	42	17

* The high nitrogen content was caused by presence of kernel residues and skins.

Groundnut hulls had a DMD of only 26%. However dry matter intake of groundnut hulls was higher: 47 g DM/W^0.75 against 42 g DM/W^0.75 for cottonseed hulls which had a higher content of digestible crude protein (40 g per kg DM). This difference was due to the presence of kernel residues and skin debris in the groundnut hulls.

In energy terms, cotton seed hulls contained 0.29 FU per kg, and groundnut hulls only 0.05 FU per kg. The much higher protein content of groundnut hulls (115 g/kg) compared with cottonseed hulls (60 g/kg,) was due to the inclusion of kernel and skin debris in the former. DCP contents differed even more, 41 g/kg versus nil.

Nutritive value of supplemented groundnut hulls and cotton seed hulls

A series of trials was carried out with cattle and sheep using supplemented rations based on groundnut hulls or cotton seed hulls. The groundnut hull incorporation rate varied from 22 to 70%; for cotton seed hulls from 25 to 90%.

The ingestibility (DMI) of rations consisting essentially of groundnut hulls reached 125 g DM/kg W^0.75 at an incorporation rate of 38.5%. At the equivalent incorporation rate (37%), rations based on cotton seed hulls recorded DMI values of up to 94 g DM/kg W^0.75. This ingestibility varied with the content of crude fibre of which the optimum content for maximal ingestion was found to be 320 g per kg (Graph 1). This relationship has not been verified with groundnut hulls.

Compounded feeds based on cotton seed hulls were more digestible (59%) than those based on groundnut hulls (47%). Wheat bran and maize bran, mixed with groundnut hull rations were higher in digestibility (DMD between 46 and 55%) and energy content (0.46 to 0.61 FU/kg). Molasses and brewers' grains improved the voluntary intake (107 g DM/kg W^0.75).

Groundnut cake combined with molasses gave diets with the highest digestible crude protein content (121 g per kg DM) (Tables 2 and 3).

Cotton seed hull rations were lower in DCP content for a particular supplementation but were higher in digestible organic matter and energy content. However, voluntary dry matter intakes of groundnut hull rations were higher despite the relatively low dry matter digestibility.

In the case of intensive animal production systems, where the objective is high production, rations based on cotton seed hulls would be advisable, because of their rather higher DOM intake (46 compared with 44g/kg W^0.75).

Graph I. Intake evolution of cottonseed hull rations in terms of their crude fiber roses

Table 2. Feed value of groundnut hull rations complemented by agro-industrial by-products.

No. of Trials	Principal concentrated feed in the ration	Intake (g/kg DM)			p.100		g/kg DM		UF	g/kgW0.75
		DM	OF	TNM	DMD	OMD	DOM	DNM	Energy	DMI	DOMI
4	Maize bran	955	355	104	55	56	540	52	0.60	93	93
11	Wheat bran	925	373	110	45	47	411	62	0.46	83	39
7	Brewers' dried grain + molasses	927	313	134	45	46	425	75	0.46	107	49
3	Groundnut cake + molasses	924	390	149	41	42	388	121	0.26	83	34

Table 3. Feed value of cottonseed hull rations complemented by agro-industrial by-products.

No. of trials	Rations description	Intake (g/kg DM)			p.100		g/kg DM		UF	g/kg W0.75
		DM	OF	TNM	DMD	OMD	DOM	DNM	Energy	DMI	DOMI
1	Cottonseed hulls 90 - cottonseed cake 10	965	475	123	54	55	532	61	0.53	93	37
1	Cottonseed hulls 82 - cottonseed cake 10 - molasses 8	936	547	84	63	62	580	34	0.63	61	38
2	Cottonseed hulls 37 - molasses 15 - wheat bran 30 cottonseed cake 6 - granicalcium 2 - salt 1	921	327	96	58	59	542	46	0.58	94	54
2	Cottonseed hull 1 25 - wheat bran 27 5 - ground sorghum 25 - groundnut cake 4 - carbonate of lime	947	282	118	61	63	528	21	0.66	83	52

Prediction of the nutritive value of rations of groundnut hulls complemented with agro-industrial byproducts from their chemical composition

Parameters used for deriving prediction equations from Dakar data are shown in Table 4. The established equations were simple (Table 5) or multiple (Table 6).

Simple equations, i.e., y = ax + b, were less precise, as shown in the correlation coefficients and standard errors, but they were easier to apply.

Dry matter and organic matter digestibilities and also the energy value of the rations were negatively influenced by crude fibre content. Food consumption was related similarly to the groundnut hull incorporation rate.

The most precise relationship was that between total crude protein content (x) and digestible crude protein content (y):

y - 0.91 x - 45.39; r = 0.95; n = 30.

Clearly these results do not include all cases likely to be encountered. However, the results obtained can be used as a working basis for future applications, particularly for field workers who do not have adequate access to means of analysis or to bibliographic facilities to allow them to reach a quick decision.

Table 4. Equations variables for nutritive value prediction of combined groundnut hull rations.

Table 5. Simple prediction equations for nutritive value of groundnut hull rations complemented with agro-industrial byproducts.

Dependant variables (y)	Independant variables	Regression equations	Standard error of estimate	Correlation coefficient	Data number
DMD (p.100)	CF (g/kg DM)	y = - 0.06 x + 66.00	7.35	0.75	30
OMD (p.100)	CF (g/kg DM)	y = - 0.06 x + 67.21	7.60	- 0.74	30
FU (/kg DM	CF (g/kg DM)	y = 0.001 x + 0.810	0.19	0.68	30
DCP (g/kg DM)	CP (g/kg DM)	y = 0.91 x - 45.39	10.19	0.95	30
DMI (g/kg DM)	Groundnut hull	y = 0.61 x + 113.88	15.13	- 0.75	30
	(p.100 of the ration)	y = - 0.38 x + 65.86	10.81	- 0.71	30
DOMI (g/kg DM)	" "	y = - 0.38 x + 65.86	10.81	0.71	30

Table 6 Multiple regression equations for predicting nutritive value of groundnut hull rations complemented with agro-industrial byproducts.

Nutritive value (dependent variable)	Multiple regression equation	Standard error of estimate	Multiple correlation coefficient	Data number
DMD	1) 0.06 NFE - 0.07 NFEF - 0.08 CFF - 0.17 Ref + 68.13	4.72	0.92	30
	2) 0.04 FU - 0.03 CFF + 0.10 CP - 0.37 Ref - 17.06	5.68	0.88	30
	3) 0.06 CF - 0.11 DM - 0.41 Ref - 31.50	6.11	0.85	30
	4) 0.04 CF - 0.04 CFF + 75.29	6.82	0.80	30
DMD	1) 0.06 NFE - 0 06 NFEF - 0.09 CFF - 93.96	4.87	0.91	30
	2) 0.03 CF - 0.03 CFF - 0.45 mot - 0.35 Ref + 84.73	5.80	0.87	30
	3) 0.04 CF - 0.04 CFF + 76.32	6.83	0.79	30
DOM	1) 0.66 NFE 0.79 NFEF - 0.91 CFF - 1.20 GH - 2.18 Ref + 83.99	44.92	0.81	30
	2) 0.31 CF - 0.36 CFF + 710.46	67.17	0.77	30
DCP	1) 0.88 NM - 0.44 CF - 24.49	8.50	0.97	30
FU	1) 0 0001 NFE + 0.38 NMF - 0.638	0.15	0.82	30
	2) 0.001 CF + 0.003 NMF + 0.400	0.17	0.76	30
DMI	1) 0 44 GH - 0.58 Ref + 121.25	15.13	0.79	30
DOMI	1) 0.06 NFE - 0.58 Ref + 20.16	7.70	0.87	30

Conclusion

Groundnut hulls and cotton seed hulls were included in a series of byproducts studied over several years in Senegal. Our interest in these two byproducts arose in the first place because they were produced near the cities and secondly because they constitute a good raw material to which to add concentrated feeds. They should find ready application in milk production and animal fattening enterprises, perhaps a more profitable use than burning them as industrial fuel in factories.

References

Mongodin B et Tascher G, 1979. Les sous-produits agro-industriels utilisables dans l'alimentation animale au Senegal. IEMVT/Ministere de la Cooperation, France.

Mbaye Nd, 1982. La problematique de l'elevage en Afrique de l'ouest; l'alimentation du betail. LNERV, Dakar.

Sall Ch, 1985. Description et premiers resultats de quatre operations de recherche sur l'alimentation des ruminants domestiques au Senegal: (3) Valeur alimentaire des rations a base de coques d'oleagineux. Memoire de confirmation. ISRA, pp 41-50.

Sansoucy R et Emery B. Utilisation actuelle des residus de recolte et sous-produits agro-industriels en alimentation animale. Production et sante animale. FAO: (32)5.