Legume supplementation of maize stover

T. Smith, B. Manyuchi and S. Mikayiri
Grasslands Research Station,
P/Bag 3701, Marondera, Zimbabwe

Abstract
Introduction
Materials and methods
Results
Discussion
Acknowledgements
References

Abstract

The value of legumes Lablab purpureus, Lablab, (LL). Vigna unguiculata, Cowpea, (CP), Cajanus cajan, Pigeonpea, (PP) as supplements to maize stover were assessed in two experiments. In the first lambs received 0, 100, 200 or 300 g of legume, with or without cottonseed meal, and maize stover ad libitum. All the legumes increased total dry matter intake (P<0.001), digestibility (P<0.05) and nitrogen retention (P<0.05). Stover intake was not increased by the legumes but was by cottonseed meal.

In the second experiment CP was compared with early (EPP) or late (LPP) cut PP as supplements to lambs receiving a small concentrate allocation and maize stover ad libitum. Total intake (P<0.001), digestibility (P<0.05) and nitrogen retention (P<.05) were increased by all legumes, especially CP. In a further trial lambs showed a marked preference for CP compared to PP especially EPP. Yield of EPP per ha was markedly lower than LPP.

The results indicate improved nutritional status in lambs receiving legumes and differences between legumes in their nutritive value and acceptability. Some of the practical implications of underfeeding and the role of legumes are discussed.

Introduction

Crop residues are an essential resource for dry season feeding of ruminants in Zimbabwe. Maize stover is the most plentiful (Sibanda, 1986; GFA, 1987) but as with all cereal stovers it has a low crude protein and high fibre content. Treatment with urea and supplementation with protein have been found beneficial when feeding cattle or sheep (Smith et al, 1988). However, oilcakes and urea are expensive and often in short supply and so other sources of nitrogen must be considered.

The addition of a small quantity of green forage residues was suggested as a means of improving rumen function (Preston and Leng, 1984). This is not practical in regions with a clearly defined long dry season. Blaxter et al (1961) showed that substitution rates of one feed for another were much lower when a good quality forage (straw) was offered with concentrates than when a good quality (hay) was offered. This concept together with the predictable response of a poor quality roughage to protein supplementation (ARD. 1984) have been brought together in the recommendations for the use of legumes as a component of dry season grazing (Rukanda; 1982; Maclaurin and Grant 1987). Mombeshora, Maclaurin and Reh (1987) discussed the establishment of fodder legumes in communal areas of Zimbabwe.

The use of legumes in intercropping with either temperate or tropical cereals has long been accepted. Dzowela (1987) summarized the effects on the cereal crop (maize) of this technique. In a series of trials the acceptability of legume stover mixtures has been assessed in sheep and cattle, using legume species known to grow in a high rainfall area (1000 mm/yr) of Zimbabwe (Clatworthy and Nziramasanga, pers comm).

Materials and methods

Statistical analysis

Three legume species, Lablab purpureus (Lablab, LL) Vigna unguiculata (Cowpea, CP) and Cajanus cajan (Pigeonpea, PP) have been used in trials with sheep and cattle to assess their value as supplements to maize stover. For the two experiments the legumes were grown separate from the maize to allow control of the legume: stover ratio in the diet. Legumes were also fed separately to the stover in order to give accurate estimates of intake.

Experiment 1

The three legumes (LL, CP, PP) were each fed as supplements (0, 100, 200, 300 g fresh material per day) to lambs receiving ad libitum maize stover with or without cottonseed meal (CSM, 140 g fresh feed per day). Seven intake, digestibility and DM retention studies were made, in the first six each legume being tested in the presence or absence of CSM and in the seventh all legumes being fed at 300 9 with CSM. The degradability of the legumes was measured using nylon bags (Orskov and McDonald, 1979) suspended in the rumens of mature fistulated steers, receiving a fixed amount of a standard diet.

The legumes and maize stover were cut at the end of the wet season, dried, baled and subsequently milled through a 14 mm screen. Chemical composition of the feedstuffs is shown in Table 1.

Initially 16 recently castrated crossbred lambs (Merino & Dorper) weighing between 20 - 30 kg (average 24.9 kg), were ranked according to liveweight and randomized to the first set of treatments. Throughout the trial losses of lambs were heavy (9 deaths) and replacements were made as appropriate. After each dietary change there was a 21 - day adaptation period followed by five days of intake measurements together with total collection of faeces and urine.

Each legume was also offered to two yearling Friesian heifers in amounts up to 2 kg/d. They also received 2 kg/d of medium quality veld hay and 2 kg of the maize/urea concentrate. This was a short study (14d) to gauge the acceptability of the legumes fed to cattle.

Table 1: Dry matter (g/kg), nitrogen and ash concentration (g/kg DM) and in vitro O.M. digestibility (DOMD%) of the feeds used in Experiments 1 and 2.

	Dry matter*	Nitrogen	Ash	DOMD%**
Expt 1:
Maize stover	928	3.8	24	48.4
Lablab	923	13.4	48	58.5
Cowpea	915	23.7	38	74.3
Pigeonpea	900	17.4	92	43.8
Cottonseed meal	930	63.3	136
Expt 2:
Maize stover	920	4.7	45	42.4
Cowpea	898	26. 2	1 00	65. 0
Early cut Pigeonpea	908	28.0	38	36.4
Late cut Pigeonpea	913	21.2	55	32.5
Urea/maize meal (1:10)	885	24.3	34

* mean values during the experiment
**Tilley and Terry (1963)

Statistical analysis

The data was subjected to analysis of variance and regression analysis when appropriate by use of the Genstat statistical package. Data derived from the nylon bag technique was fitted to the model of Orskov and McDonald (1979).

Results

Variation between groups in liveweight increased, especially in the later stages of Expt 1, and so intake and N retention data are presented on the basis of metabolic liveweight (g/kg^0.73).

Experiment 1

Both LL and CP were readily eaten but there was initial resistance to PP. To overcome this, PP was mixed with CSM for the first study with this legume. The results will be presented in chronological order although for simplicity Table 4 follows the same format as Tables 2 and 3.

Lablab In the absence of CSM, successive increments of LL increased daily total intake (P<0.001) but reduced intake of stover above 100 g of LL (P<0.05) (Table 2). Dry matter digestibility was increased and that of acid detergent fibre decreased by the increments. Lablab increased N intake and retention (P<0.05).

Table 2. Daily intake (gDM/kg^0.75), N retention (g/kg^0.73) and digestibility (%) of diets based on maize stover supplemented with Lablab and offered to lambs.

	No cottonseed meal					Cottonseed meal (140 g/d)
Lablab (g/d)	0	100	200	300	SED	0	100	200	300	SED
Total intake	19.7a	29.5b	31.4bc	37.0c	1.95	47.2a	55.3b	60.4bc	66.5c	1.68
Stover intake	19.7bc	21.0c	15.4ab	12.1a	1.39	35.1c	34.2bc	31.5b	27.6a	1.01
DM dig	47.9a	52.8a	55.2a	54.8a	3.81	53.4a	55.4a	55.5a	55.4a	1.09
Acid detergent fibre dig	56.1a	53.8a	50.8a	46.9a	4.34
N retention	-0.104a	0.002b	0.036b	0.036b	0.131c	0.0226	0.466a	0.553ab	0.571ab	0.0421
Crude protein % of diet	2.4	4.1	5.5	6.4		11.9	11.5	11.3	11.6
Change in stover intake (g)/g legume	x	0.15	-0.27	-0.31		x	-0.10	-0.21	-0.28
Change in total intake (%)	x 49.7	59.4	87.8			x	17.2	28.0	40.9

Means in the same row with different superscripts are significantly different (P<0.05).

The addition of CSM to the diet substantially increased stover intake' N intake and N retention but did not affect the pattern of response. Without LL the digestibility of DM was increased by CSM but where LL was fed the changes due to CSM were small.

Cowpea: Successive increments of CP, with or without CSM, increased total intake (P<0.001), digestibility of DM (P<0.05) and N intake. In the absence of cottonseed meal organic matter digestibility (P<0.05) and N retention (P<0.01) were increased by CP. Faeces samples collected when the lambs were receiving CSM were wrongly bulked and, therefore, organic matter digestibility and N retention data is not available. The addition of CSM increased stover intake. There was also a change in the pattern of intake, without CSM a small non-significant increase as CP increased was changed, with CSM, to a small non-significant decrease (Table 3).

Pigeonpea: Total intake was increased by the addition of PP (P<0.05) and generally stover intake fell (P<0.05) (Table 4). The higher total intake with CSM was due entirely to the CSM. Digestibility of dry and organic matter was unaffected by the addition of legumes or CSM. However, N intake and retention were increased by both legumes and SCM, the differences without CSM being significant (P<0.001).

Three legumes: When the three legumes were offered at 300 g/d with CSM they all increased total intake compared to maize stover with CSM and legume (P<0.001) (Table 5). Stover intake was greatest with CP and least with PP (P<0.05). Digestibility of dry and organic matter was increased by all the legumes especially LL and CP (P<0.05). All legumes increased N intake and retention especially CP (P<0.001).

Dry matter and N disappearance: The loss of DM and N together with estimates of degradability constants a, b and c are shown in Table 8. Cowpea had the greatest extent of DM and N loss followed by LL and PP. Rates of degradability (dg) of CP and LL were similar.

Experiment 2

Total intake was increased by all the legumes (P<0.05) (Table 6) and especially CP (P<0.001). Stover intake was reduced by the inclusion of LPP (P<0.01). Early cut pigeonpea was not readily eaten. Improvements in the digestibilities of dry matter (P<0.05) and organic matter occurred with all legumes especially CP and LPP. Nitrogen retention was also increased by all the legumes (P<0.05).

Table 3: Daily intakes (0 M/kg^0.73), N retention (g DM/kg^0.73) and digestibility (%) of diets based on maize stover supplemented with Cowpea and offered to lambs.

	No cottonseed meal					Cottonseed meal (140g/d)
Cowpea (g/d):	0	100	200	300	SED	0	100	200	300	SED
Total intake	26.9a	36.4b	45.0b	54.3c	2.92	54.5a	58.2a	68.1b	72.1a	3.13
Stover intake	26.9a	28.1a	28.5a	29.8a	2-70	42.1a	38.6a	40.0a	37.9a	2.52
DM dig	33.4a	45.9b	51.1b	55.7b	3.20	48.9a	49.8ab	52.1b	53.2b	1.14
Organic matter dig.	38.7a	48.9b	53.1b	57.1b	2.70
N retention	-0.243a	-0.080b	0.030c	0.139d	0.0258	x	x	x	x	x
Crude protein % of diet	2.4	5.2	6.9	8.0		10.8	11.5	11.7	12.0
MEMJ/d	0.158	0.269	0.362	0.469
Change in stover intake (g)/g legume	x	0.14	0.10	0.12		x	-0.43	-0.13	-0.18
Change in total intake (%)	x	35.3	67.3	101.9		x	6.8	25.0	32.3

Means in the same row with different superscripts are significantly different (P<0.05)

Table 4. Daily intakes (g DM/kg^0.73), N retention (g/kg^0.73) and digestibility (%) of diets based on maize stover supplemented with Pigeonpea and offered to lambs.

	No cottonseed meal					Cottonseed meal (140 g/d)
Pigeonpea (g/d):	0	100	200	300	SED	0	100	200	300	SED
Total intake	34.2a	37.0ab	45.9bc	52.7c	3.28	42.1a	45.0ab	64.6c	59.7bc	5.28
Stover intake	34.2a	29.0a	31.3	31.3a	3.39	30.6a	26.2a	35.0a	25.5a	3.92
DM dig	42.0a	39.4a	42.4a	40.4a	2.83	35.5a	39.5a	36.0a	4.38
Organic matter dig	40.6a	37.7a	40.7a	38.6a	2.91	347.8a	35.2a	39.5a	38.5a	4.22
N retention	-0.145a	-0.078ab	0.012bc	0.027c	0.0282	0.356a	0.428a	0.535a	0.400a	0.0790
Crude protein % of diet	2.4	4.2	5.0	5.8	12.6	13.0	11.8	12.7
MEMJ/d	0.211	0.210	0.278	0.300	0.235	0.232	0.373	0.331
Change in stover intake (g)/g legume	x	-0.64	-0.2	-0.14		x	-0.57	+0.26	-0.22
Change in total intake %	x	8.5	34.2	54.1		x	6.9	53.4	41.8

Means in the same row with different superscripts are significantly different (P<0.05)

When the lambs were allowed to select their diet CP was the preferred forage. When CP was omitted LPP was eaten more readily than EPP and maize stover intake increased substantially (Table 7). Water intake was approximately 2.7 1/kg DM. Yearling heifers ate EPP more readily than the lambs but CP was the most readily eaten.

Table 5: Daily intakes (gDM/kg^0.73), N retention (g/kg^0.73) and digestibility of diets based on maize stover plus cottonseed meal (130 gDM/d) and supplemented with Lablab, Cowpea or Pigeonpea (300 g fresh/d) offered to lambs

	Treatments
	Control	Lablab	Cowpea	Pigeonpea	SED
Total intake	52.5a	75.0bc	80.1c	71.5b	2.47
Stover intake	41.4ab	41.6ab	43.8b	37.2a	1.95
DM dig (%)	53.5a	60.3b	60.0b	57.9ab	1.72
Organic matter	55.7a	60.0b	61.9b	58.8ab	1.93
N retention	0.339a	0.600b	0.831b	0.571b	0.0386
Crude protein % of diet	10.2	9.6	11.7	10.9
MEMJ/d	0.434	0.689	0.739	0.615
Change in stover intake (%) (g)/g legume	x	0.01	0.10	-0.18
Change in total intake (%)	x	42.9	52.6	36.2

Means in the same row with different superscripts are significantly different (P<0.05).

Table 6: Daily intakes (gDM/kg^0.73), N retention (g/kg^0.73) and digestibility of diets based on maize stover and supplemented with early cut pigeonpea (EPP), late cut pigeonpea (LPP) or cowpea (CP) and a urea maize mix (177 g DM/d) offered to lambs.

	Treatments
	Control	CP	EPP	LPP	SED
Total intake	48.7a	64.4c	58.0bc	53.9ab	2.41
Stover intake	34.6b	31.0b	32.4b	22.2a	1.57
DM dig (%)	49.3a	55.3b	51.2b	56.0b	1.79
Organic matter dig (%)	50.7a	56.4a	52.4a	53.1a	2.91
N retention	0.132a	0.381b	0.319b	0.311b
Crude protein % of diet	6.5	9.7	8.8	9.5
MEMJ/d	0.369	0.532	0.449	0.426
Change in stover intake (%) (g)/g legume	x	-0.18	-0.18	-0.69
Change in total intake (%)	x	32.2	19.1	10.7

Means in the same row with different superscripts and significantly different (P<0.05).

Table 7: Total daily intake (gDM; gDM/kg^0.73) and % contribution of individual feeds to the total.

	Pen Number
	1	2	3	4
Total intake: (g/d)	1213	1303	1159	665
(g/kg0.73)	97.4	99.3	88.0	53.1
Urea-maize mixx	14.6	13.6	15.3	26.6
Cowpea	72.0	71.1	73.1	x
Early cut Pigeonpea	x	3.3	5.3	8.1
Late cut Pigeonpea	7.0	4.8	x	23.1
Maize stover	6.4	7.2	6.4	42.2

^x Fed at a fixed amount of 177 gDM/lamb/day

Dry matter and N disappearance from nylon bags suspended in the rumens of fistulated steers was in the order: LPP EPP CP (Table 8).

Table 8: Drymatter (DM) and nitrogen (N) loss (%) from legumes incubated in nylon bags in the rumen of fistulated steers.

		Fitted constants for model P = a + b (1-e-ct)+				Loss % of DM and N Incubation time (hours)
		a	b	c	3	6	12	24	36	48
Experiment 1
Lablab	DM	24.0	37.0	0.06	x	35.3	44.5	49.8	58.3	61.0
	N	58.8	26.2	0.08	x	66.9	77.9	77.2	84.0	84.6
Cowpea	DM	42.8	34.2	0.06	x	53.0	59.0	66.0	73.0	77.0
	N	61.5	26.6	0.06	x	70.2	75.2	80.2	87.3	87.6
Pigeonpea (PP)	DM	26.6	23.4	0.04	x	32.3	35.8	36.3	43.3	49.8
	N	32.8	32.2	0.03	x	38.7	41.0	45.0	50.8	64.4
Experiment 2
Cowpea	DM	36.4	34.6	0.06	42.8	46.6	54.4	63.2	x	70.1
	N	66.4	22.6	0.09	71.0	75.9	81.8	84.6	x	88.9
Early cut PP	DM	24.3	27.7	0.05	28.0	32.5	35.7	42.2	x	52.0
	N	53.0	29.0	0.06	56.0	64.8	66.4	74.0	x	81.8
Late cut PP	DM	21.3	24.7	0.07	24.2	31.3	35.1	39.0	x	45.9
	N	48.9	26.6	0.10	53.9	66.4	67.9	70.0	x	75.3

+ Ørskov and McDonald (1979).

Discussion

When fed in fixed amounts all the legumes used in both experiments increased total DM intake' digestibility and N retention. Substitution of stover by legumes was highest with PP, the mean effect of PP in Expt 1 and LPP in Expt 2 being a reduction in stover intake of 0.3 g DM per g of PP consumed. Digestibility of DM and organic matter was consistently increased when LL and CP were fed, especially with the lower levels of supplementation in Expt 1. With PP the pattern was not so clear. Generally CSM increased stover intake and digestibility of those diets not containing LL or CP. The reasons for the lack of response to CSM when PP was fed in the first phase of Expt 1 (Table 4) are not clear. It was not possible to carry out acid detergent fibre analysis on all samples. The results are similar to those observed in goats receiving maize stover supplemented with leucaena hay (Banda and Ayoade, 1986).

Energy requirements of lambs fed indoors are 0.414 MJ per kg^0.73 (ARC, 1980). By converting digestible organic matter intake (DOMI) to ME (DOMI (kg) × 15.6 (ARC, 1980) inspection of the available data show that lambs received maintenance only with CSM, concentrates or 300 g CP, although by increasing total intake all legumes raised ME intake.

Nitrogen retention was increased by all legumes and CSM. Broster et al. (1978) reported excess N to be excreted in the urine and N supplements to have little effect on faecal N, in steers receiving fixed amounts of energy. In these experiments faecal N was increased by the legumes suggesting that although N loss after a fixed time, from nylon bags was high, turnover rates were also high resulting in low digestibility.

Regression analysis showed that N retention (NRg/d) was affected by N intake (N/g/d) and DOMI (kg/d) as follows

NR = -1.90 + 0.603 (±0.0233)NI (r=0.885) (1)
NR = -3.26 + 0.022 (±0.0013) DOMI + 0.634 (±0.0337)NI
(r=0.936) (2)

Equation 1 was derived from all NR data of Expt 1 and equation 2 from the same data where estimates of DOMI were also available. Using equation 1 the missing NR data for CP = CSM (Table 4) becomes: 0.389, 0.477; 0.601; 0.677 (g N/kg^0.73/d) for 0, 100, 200, 300 g CP respectively.

The low intakes of ME and low NR in the first phase of Expt 1 and equation 2 from the same data where estimates of DOMI were also available. Using equation 1 the missing NR data for CP + CSM (Table 4) becomes: 0.389; 0.477; 0.601; 0.677 (g N/kg^0.73/d) for 0, 100, 200, 300 g CP respectively.

The low intakes of ME and low NR in the first phase of Expt 1 probably contributed to the high rate of lamb mortality. Two thirds of the original lambs under 25 kg initially and one third over 25 kg died. Although most of the deaths were explainable it is likely that nutritional stress increased susceptibility to disease in young animals. subsequently a small concentrate allowance removed the problem.

In Expt 2 EPP had a higher N content and in vitro DMD% than the LPP but was less readily eaten, especially by lambs. This could be caused by either a very low level of mould, reflecting the difficulties of making hay in the wet season, or toxins. The yields (kg/ha) of DM and crude protein for EPP and LPP were respectively: 2113, 394 and 2974, 370. A second cut of the area used for EPP was not possible because of insufficient regrowth. In Expt 2 the preferred legume was CP (Table 7) but in the absence of CP intakes of maize stover and LPP increased. Water intake during this period was 2.7 1/kg DM eaten, higher than the 2 1/kg DM suggested for growing lambs in temperate climates (ARC, 1980).

The data suggests that the legumes were used as supplements and had little effect on the utilisation of the stover. This probably reflects their bulkiness and relatively low crude protein concentration compared to CSM, which did increase intake of stover. However, legumes are relatively cheap to grow and often occur as by-products of human food or cash crops. These factors together with the agronomic advantages of growing legumes must be compared with other methods of supplementing and upgrading roughages (Sundstol and Owen, 1984; Smith et al, 1988). The cost of new technologies must be recovered from extra produce for sale (Orskov, 1987) or for the farmer's own use. In practice a combination of upgrading and supplementation will probably be most beneficial.

Acknowledgements

We are grateful to Dr. J.N. Clatworthy for helpful discussions, L. Nziramasanga for supplying legume hays, E. Rusike, R. Chiwawa, J. Chabona, L. Svishvah and their staffs for care of the animals and chemical analysis, and Mrs. B. Chakanyuka for statistical analysis.

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