The feeding value of crop residues from sorghum, pearl and finger millet cultivars

S Ncube and T Smith

Matopos Research Station
Private Bag K 5137, Bulawayo, Zimbabwe

ABSTRACT

Two experiments were conducted to evaluate the value of sorghum and millet residues as feeds for indigenous sheep. In the first, wethers received a daily diet of 100 g cottonseed meal plus hay (control) or one of the following stovers ad libitum: sorghum (white, SVI; or red, DC75); pearl millet (white, SDMV 89004; or red NCD2); finger millet (white, SDFM 63; or red, 25C). Nitrogen (N) and neutral detergent fibre (NDF) concentrations differed between species but not variety. Finger millet stover contained most N and least NDF, was most readily eaten (P<0.05) and resulted in the highest N retention and the lowest NDF digestibility. In the second experiment wethers received one of the following diets: hay plus 100 g/day cottonseed meal (control); threshed heads of white (SVI) or red (DC75) sorghum, with or without 100 g/day cottonseed meal; or threshed heads of red finger millet (25C). Finger millet heads contained most N and least NDF and were most readily eaten and digested (P<0.05). The addition of cottonseed meal was beneficial and SVI was more digested than DC75.

RESUME

Valeur nutritive de résidus de cultivars de sorgho, de mil perlé et d'éleusine

Deux expériences ont été effectuées en vue d'évaluer les résidus de sorgho, de mil perlé et d'éleusine dans l'alimentation des ovins. Dans la première étude, les animaux avaient été soumis à une ration composée de 100 g de tourteau de coton par jour et de foin (témoin) ou de paille d'une des céréales suivantes offerte ad libitum: sorgho (blanc, SVI; ou rouge, DC75); mil perlé (blanc, SDMV 89004; ou rouge NCD2); éleusine (blanche, SDFM 63; ou rouge, 25C). Les concentrations en azote et en parois cellulaires étaient différentes entre espèces mais non entre variétés. Avec la teneur en azote la plus élevée et la concentration en parois cellulaires la plus faible, L'éleusine était plus volontiers consommée (P<0,05) et donnait lieu à une rétention d'azote maximum et une digestibilité minimum des parois cellulaires. Dans la seconde expérience, les animaux étaient soumis à l'une des rations suivantes: foin plus 100 g de tourteau de coton par jour (témoin); épis égrenés de sorgho blanc (SVI) ou rouge (DC75) seuls ou avec 100 g de tourteau de coton par jour; ou épis égrenés d'éleusine (25C). Les épis d'éleusine avaient la teneur la plus élevée en azote et la plus faible en parois cellulaires, et étaient plus consommés et plus facilement digérés (P<0,05). L'addition de tourteau de coton était bénéfique pour les animaux et le cultivar du sorgho SVI était plus facilement digéré que le DC75.

INTRODUCTION

The constraints to livestock production from feeding large quantifies of fibrous byproducts are known (Sundstol and Owen, 1984), as are interventions which can ameliorate them. However, much of the information has been derived from temperate crops and in circumstances where inputs, such as chemicals and protein supplements, are available and affordable. In much of Africa maize, sorghum and millet are the major cereal crops and there is little scope to purchase inputs for livestock production. In some areas of Zimbabwe up to 50% of dry-season feeding can come from crop residues.

In Zimbabwe maize is the preferred staple but because of low rainfall and short grazing seasons in natural ecological regions IV and V (Johnson, 1987) sorghums and millets are recommended by researchers and extension staff. Total crop-residue production in 1989/90 from the three major cereals, based on preliminary estimated forecasts of grain yield (Kossila, 1988; CSO, 1990), amounted to more than 5.5 million tonnes. Methods for improving the utilisation of maize stover have been reported (Manyuchi et al, 1990). Work is now in progress to evaluate sorghum and millet residues as livestock feeds.

MATERIALS AND METHODS

Two experiments were conducted to measure intake, digestibility and nitrogen retention (NR) of sorghum and pearl and finger millet residues.

In one experiment, 35 indigenous wethers (average initial liveweight 34 kg; age about 18 months) were allocated at random to one of seven treatment groups (five animals each):

· hay (control)
· white sorghum stover (SVI)
· red sorghum stover (DC75)
· white pearl millet stover (SDMV 89004)
· red pearl millet stover (NCD2)
· white finger millet stover (SDFM 63)
· red finger millet stover (25C).

All animals in this trial also received 100 g cottonseed meal (CSM) per day.

The second experiment used 30 of the wethers from the first experiment, after they had grazed on veld for one month: their average initial liveweight was 31 kg. They were allocated at random to six treatments (five animals each):

· hay plus 100 g CSM/day (control)
· threshed heads of white sorghum (SVI) with or without 100 g CSM/day
· threshed heads of red sorghum (DC75) with or without 100 g CSM/day
· threshed heads of red finger millet (25C), alone.

Cereal heads were threshed using a mechanical thresher. Residues were milled using a 25-mm screen and offered to sheep ad libitum at 0800 and 1400 hours daily. Sheep were individually penned; water was always available. Intake was measured after 21 days acclimatisation, after which 80% of ad libitum intake was fed prior to measuring digestibility and nitrogen retention. A seven-day period was allowed for adjustment to the digestibility crates. Faeces and urine were weighed daily, subsampled and stored at -20°C to await analysis.

RESULTS

Experiment 1

Neutral detergent fibre (NDF) and nitrogen (N) contents of the stovers were different between species (Table 1) but not between varieties within species. Finger millet contained most N and least NDF. The hay used contained less N and more NDF than the residues. Intake was highest (P<0.05) with finger millet and lowest with hay and SDMV pearl millet (Table 2): differences between pearl millet varieties may have been due to traces of mould in SDMV. Dry-matter (DM) and organic-matter (OM) digestibilities were lowest for hay (P<0.05), and NDF digestibility was lowest in the finger millets (P<0.05). (The differences in digestibility between sorghum varieties were probably due to a higher concentration of phenolics in DC75.) Nitrogen retention was greatest with finger millet, especially 25C, and least with hay (P<0.05).

Experiment 2

The threshed stover heads contained about 70 g grain/kg DM. Finger millet heads contained most N and least NDF (Table 1). Heads of red sorghum contained more N than those of white sorghum. Intake was highest with finger millet heads and lowest with hay (P<0.01). CSM increased (P<0.05) intake of the sorghum heads, especially DC75 (Table 3). DM and OM digestibilities were greatest with finger millet and DC75 plus CSM and least with hay (P<0.05). Intake and digestibility of both sorghums were enhanced by CSM; SVI was more digestible than DC75. Digestibility of NDF was greatest with SVI plus CSM and hay and least with DC75 alone and finger millet (P<0.05). Nitrogen retention was increased by CSM and finger millet (P<0.05).

Table 1. Chemical composition of stovers heads

Roughage		Chemical composition (g/kg DM)
		Dry matter (g/kg)	Nitrogen	Neutral detergent fibre	Organic matter
Hay		941	6.1	861	940
Stovers
Sorghum
	SVI	938	8.6	162	935
	DC 75	932	8.8	765	923
Pearl millet
	SDMV 89004	935	10.2	784	902
	NCD 2	938	10.4	777	901
Finger millet
	SDFM 63	918	15.5	605	901
	25C	925	17.0	637	906
Threshed heads
Sorghum
	SVI	917	8.5	710	946
	DC 75	918	14.2	776	949
Finger millet
	25 C	888	18.9	434	929

DISCUSSION

The results confirm earlier reports (Smith and Balch, 1984) that low protein and high fibre reduce the nutritional value of cereal residues. Intakes of the residues used here were much higher than those reported in lambs receiving maize stover supplemented with urea (Manyuchi et al, 1990) or CSM (Smith et al, 1990), probably reflecting the relatively low N content of maize stover.

Quantities of threshed heads available are minimal compared to stover. The retained grain in the heads (about 70 g/kg DM) would have contributed to their acceptability as feed. The finger millet heads could probably be effectively used as a supplement to dry-season grazing or stover diets.

In another study, the grains removed from sorghum (SVI) and pearl millet (SDMV) stovers were compared as replacements for maize grain in high-energy finishing diets for steers (Nengomasha et al, in press). The results indicate that these two varieties can replace maize grain in fattening diets.

The study of sorghums and millets is continuing with emphasis on the effects of agronomic and handling techniques on stover yield and quality.

Table 2. Voluntary intake, digestibility and N. retention in sheep fed sorghum and pearl and finger millet stovers

Roughage		Intake		Digestibility (g/kg DM)			N retention
		g/day	g/kg0.75	Dry matter	Organic matter	Neutral detergent fibre	g/day	g/kg N intake
Hay		690	49.4	456	483	554	1.78	213
Sorghum
	SVI	874	61.1	548	559	583	4.03	352
	DC 75	900	62.9	502	521	565	3.69	316
Pearl millet
	SDMV 89004	684	48.8	498	504	544	4.70	429
	NCD 2	957	66.8	510	528	570	3.65	292
Finger millet
	SDFM 63	1054	75.8	523	539	459	6.76	375
	25 C	1017	72.1	517	540	482	9.23	482
SE		40.6	3.1	0.66	0.65	0.96	0.46

Table 3. Voluntary intake, digestibility and N retention in sheep fed sorghum and finger millet threshed heads

Roughage		Intake		Digestibility (g/kg DM)			N retention
		g/day	g/kg0.75	Dry matter	Organic matter	Neutral detergent fibre	g/kg	g/day N intake
Hay		708	57.4	492	521	481	3.54	378
Sorghum
	SVI	1090	87.5	493	505	444	2.34	312
	SVI + CSM	1262	101.2	563	585	528	5.63	392
	DC 75	888	69.8	446	443	403	2.91	282
	CD 75 + CSM	1141	89.3	513	531	443	7.20	341
Finger millet
	25 C	1409	110.3	570	589	413	9.27	428
SE		81.1	5.62	1.39	5.46	0.98	0.47

ACKNOWLEDGEMENTS

We thank Dr S C Gupta and SADCC/ICRISAT for supplying the residues. We also thank Mr N Jele and his staff for care of the animals, and Mr J S Dube and his staff for chemical analysis.

REFERENCES:

Central Statistical Office (CSO). 1990. Report of Crop Forecasting Committee, March 1990. Government Printers, Harare, Zimbabwe. 1 p.

Johnson P (ed). 1987. Recommendations for cropping in the semi-arid areas of Zimbabwe. Agritex, Harare, Zimbabwe. 97 pp.

Kossila V. 1988. The availability of crop residues in developing countries in relation to livestock populations. In: Reed J D, Capper B S and Neate P J H (eds), Plant breeding and the nutritive value of crop residues. Proceedings of a workshop held at ILCA, Addis Ababa, Ethiopia, 7-10 December 1987. ILCA (International Livestock Centre for Africa), Addis Ababa, Ethiopia. pp. 29-39.

Manyuchi B. Ncube S and Smith T. 1990. Optimising crop utilization in Zimbabwe. Animal Production 50:589 (Abstract).

Nengomasha E M, Hatendi P R. Gupta S C and Smith T. Sorghum and pearl millet as energy substitutes for maize grain in high energy pen-fattening diets. In: Division of Livestock and Pasture Annual Report. Department of Research and Specialist Services, Harare, Zimbabwe (in press).

Smith T and Balch C C. 1984. Implications of a more widespread use of straw and other fibrous by-products as feed. In: Sundstol F and Owen E (eds), Straw and other fibrous by-products as feed. Elsevier, Amsterdam, The Netherlands. pp. 575-604.

Smith T. Manyuchi B and Mikayiri S. 1990. Legume supplementation of maize stover. In: Dzowela B H. Said A N. Asrat Wendem-Agenehu and Kategile J A (eds), Utilization of research results on forage and agricultural by-product materials as animal feed resources in Africa Proceedings of the first joint workshop, held in Lilongwe Malawi, 5-9 December 1988. PANESA/ARNAB (Pasture Network for Eastern and Southern Africa/African Research Network for Agricultural By-Products). ILCA (International Livestock Centre for Africa), Addis Ababa, Ethiopia. pp. 302-320.

Sundstol F and Owen E (eds). 1984. Straw and other fibrous by-products as feed. Elsevier, Amsterdam, The Netherlands. 604 pp.