Nutritive value of Crotalaria ochroleuca: II The effect of supplementation on feed utilisation and performance of growing sheep

S.V. Sarwatt¹, F.E.J. Mkiwa¹, A.B. Lwoga¹ and B.H. Dzowela²

¹ Sokoine University of Agriculture, Morogoro, Tanzania
² PANESA Coordinating Unit, ILCA, Nairobi, Kenya

Abstract
Introduction
Materials and methods
Results and discussion
Conclusions
Acknowledgements
References

Abstract

A study was carried out to determine chemical composition of Crotalaria ochroleuca "marejea" at three stages of growth pre-anthesis, anthesis and post-anthesis. Feeding trials were conducted to study the effect of "marejea" supplementation of low quality Chloris gayana hay on the growth rate and feed utilisation of growing sheep. In the feeding trials 12 young male sheep were randomly allocated to four treatments: hay only (T₁), hay + 1509 "marejea" (T₂), hay + 3009 "marejea" (T₃) and hay + ad lib "marejea" (T₄).

The crude protein (CP) content was highest (30.5%) at pre-anthesis and decreased with advancing plant growth. The leaves with a CP of 34.5% were observed to be the most nutritious part of the plant. The crude fibre (CF) content was lowest at pre-anthesis (36.7%) and increased to 40.0% at post-anthesis stage of plant growth. Calcium and phosphorus contents were highest at pre-anthesis.

Supplementation had a significant (P<0.01) effect on total and daily weight gain. Total and daily weight gain increased with increasing level of "marejea" supplementation in the diet but there was no significant differences (P>0.01) among supplemented animals in treatments T3 and T4. Supplemented animals as a group had significantly (P<0.01) higher daily gain than their unsupplemented counterparts.

"Marejea" supplementation increased dry matter digestibility (DMD) of hay but only significantly (P<0.01) with treatment T₄.

CP digestibility in T₄ was about three times that of the unsupplemented group (T₁). The organic matter digestibility (OMD) increased with supplementation but was significantly (P<0.01) higher only in treatment T₄. Both faecal N and and urinary N excretion increased with increased N intake and level of supplemention. The nitrogen balance value increased with increasing level of "marejea" supplementation. It was negative in treatment T₁ and highest in T₄.

From the study it was concluded that "marejea" hay at pre anthesis stage had the highest nutritive value and can be used as a cheap alternative protein supplement for growing sheep in areas where conventional proteins are expensive or not available.

Introduction

Tropical grasslands support low levels of production due to their low nutritive value of the forages (Humphreys, 1978). The potential for much greater production are obvious but first the problem of nutritional deficiency must be solved. Among the ways of improving the nutritional status of these grasslands is the incorporation of forage legumes into the grasslands through oversowing or direct inclusion of the legume in the diet of livestock. Supplementation of forage legumes in the diet of livestock seems to offer a better alternative for small-scale farmers.

One legume that is used in the southern part of Tanzania for improving soil fertility and combating weeds is Crotalaria ochroleuca locally known as "marejea" Efforts of introducing this legume in the southern part of the country are through the hard work of the Benedictine Fathers at Peramiho particularly Fr. Gerold Rupper. It is interesting to note that the people in this area adopted the use of "marejea" before any research information about the legume was known. The motive behind the quick adoption of the legume as suggested by Lupanga et al (1987) was monetary value from either the sale of the seeds or money saved by using "marejea" as a substitute for fertilizers which are expensive. Another reason was the incentive and small presents given by Fr.

Gerold during his visits (Lupanga et al, 1987). According to Lupanga et al., 1987, if markets for seeds had dried up, the farmers might have discontinued the use of "marejea" Few farmers who have goats and/or dairy cows feed "marejea" to their animals. Although no quantified data is available on the feeding value of "marejea" to livestock, the performance of the animals is reported to be good. The potential of "marejea" in the farming systems of Tanzania and particularly as a feed for livestock has been pointed out by Sarwatt (1986); Sarwatt and Mkiwa (1987); and Sarwatt and Mkiwa (1988).

This study was, therefore, undertaken to determine the chemical composition of "marejea" and evaluate its feeding value through digestibility, growth and intake trials.

Materials and methods

Forage production and preparation
Digestibility study
Intake study
Growth study
Chemical and data analyses

Forage production and preparation

During the long rains in March, 1987 an area of 0.5 ha was ploughed, harrowed and "marejea" seeds broadcasted at a rate of 10 kg/ha. A triple super phosphate (TSP) fertilizer was applied at a rate of 40 kg/ha. At three stages of growth i.e. at pre-anthesis, anthesis and post-anthesis random samples were collected for chemical analysis. The forage used in the feeding experiment was harvested at anthesis. The forage was air dried under shade in a barn. When the material was well dried, the less woody stems were separated from the rest of the plant, collected and stored in gunny bags.

Rhodes grass hay was prepared from established plots at the University Farm. The hay was cut at post-flowering stage using a forage chopper. The material was wilted for a day in the sun and final drying was done in the barn. The hay was then stacked in the barn ready for the feeding trials.

Digestibility study

Twelve male adult Black Head Persian sheep of an average weight of 30.4 kg were used for the digestibility experiment. The animals were randomly alloted to the four dietary treatments (T₁ - T₄) in a completely randomized design. The animals were welshed before and after each experimental period which consisted of a 7-day preliminary period followed by a 7-day collection period. All the animals were dewormed before the trial began.

The volume of urine was recorded daily, and 10% aliquots were combined for each sheep in each period. Daily faecal samples were dried at 60°C, samples from sheep on the same treatment were composited for analysis.

Intake study

Fourteen days after the digestibility study, the same animals and treatments were used to determine intake. The animals were weighed at the beginning and end of the preliminary period of 10 days, and at the beginning and end of the 10 day collection period. Rations were offered ad libitum so as to allow for a minimum of 20% refusals. During the preliminary period the animals were allowed to attain the highest DM intake. All the refusals were collected and weighed. From the weight of the refusals intake per metabolic body weight (g/kg W^0.75) was determined.

Growth study

Twelve male Black Head Persian sheep of an average weight of 17.2 kg were assigned at random in a completely randomized design to the four treatments (T₁ - T₄). The animals were grazed for 8 hours daily on paddocks consisting mainly of Rhodes grass and then subjected to the four treatments. All the animals were in addition, given 4g mineral mixture and water ad libitum. The animals were weighed at weekly intervals during the experimental period of 90 days. From day 88 to day 90 all the animals were weighed daily in order to determine the final average live weight.

To determine the quality of the pasture on which the animals were grazing, the animals were followed twice every week during the whole experimental period. Forage samples were plucked from the grazing sites oven dried and bulked. At the end of the study, the bulked forage was sub-sampled for the analysis of its chemical composition.

Chemical and data analyses

All the dried samples of feeds, refusals and faeces were milled through a 1-mm screen before they were analysed. Analyses for dry matter (DM), organic matter (OM), crude protein (CP) and fibre (CF), ash and either extract (EE) were conducted according to the standard procedures (A.O.A.C. 1960; 1965). The urine samples were analysed for nitrogen by the routine Kjeldahl method (A.O.A.C., 1960). Some of the samples were sent to the National Institute of Animal Science in Denmark for detailed analysis of the plant parts. The results are presented in Table 2.

The data from the digestibility, intake and growth studies were analysed in a completely randomized design as described by Snedecor and Cochran, (1980). Differences among treatment means were analysed using Duncan's multiple range test (Duncan, 1955).

Results and discussion

Intake and digestibility study
Growth study
Nitrogen balance

The chemical composition of the forages

The chemical composition of "marejea" harvested at pre-anthesis, anthesis and post-anthesis, Rhodes grass hay and that of pasture grazed by sheep in the growth study is shown in Table 1. The CP was noted to decrease with advancing stage of growth while CF increased with advancing growth. Mkiwa (1987) reported crude protein values of 28.2%, 25.6% and 17.1% when "marejea"s were harvested at 6th, 10th and 12th weeks, respectively. These values do not differ much from those obtained in this study. Rhodes grass hay was of low nutritive value as indicated by the low CP of 5.8% and high CF of 36.5%.

Table 1: Chemical composition of "marejea" hay at pre-anthesis, anthesis and post-anthesis, rhodes grass hay, and pasture fed to sheep in the growth study (DM basis).

Nutrient	Pre-Anthesis	Anthesis	Post-Anthesis	Rhodes grass hay	Pastures
DM content (%)	81.2	85.4	87.3	88.0	90.0
Organic matter (%)	73.8	76.9	81.1	80.2	88.3
Crude protein (%)	30.5	25.1	18.5	5.8	14.7
Crude fibre (%)	36.7	38.4	40.0	36.5	24.6
Ether extract (%)	2.3	3.0	1.9	1.6	2.7
Ash (%)	7.4	8.5	6.2	8.7	8.4
Calcium (%)	0.77	1.54	1.21	0.1	0.3
Phosphorus (%)	0.30	0.38	0.26	0.01	0.1

The high CP values in the pasture could be attributed to the hand plucking of pastures that consisted of several grass species, leguminous plants and shrubs. Hand plucking of the pasture after the grazing animals does not accurately represent what the animal consumes. But this was the best alternative estimation that could be used when there were no fistulated animals.

Detailed chemical composition of "marejea" plant parts is given in Table 2. The CP of the leaves of 34.5% and CF of 14.3% indicates that the leaves are the most nutritious part of the plant. The amino acids lysine and methionine in "marejea" leaves are much higher than in lucerne, though when expressed as a percentage of protein, the values are more or less the same in the two forages. The Ca and P contents in "marejea" leaves are not as high as in lucerne, but the levels are adequate to meet most of the livestock requirement (NRC, 1979).

Table 2: Detailed chemical composition of "marejea" plant parts (% DM)

Nutrient	Leaf	Leaf stalk	Stem
DM	19.1	20.2	25.4
CP	34.5	13.9	6.3
EE	7.2	2.5	1.4
CF	14.3	42.7	59.5
Ash	8.6	10.1	6.8
Insoluble fibre	34.4	60.7	76.1
Soluble fibre	3.9	5.4	3.5
Starch and Sugar	2.9	2.9	1.7
g calg	4.9	4.2	4.4
Lysine g/16g N	4.7	4.1	2.4
Methionine g/16g N	1.5	1.0	0.9
Ca	0.80	0.36	0.20
Mg	0.50	0.33	0.16
P	0.35	0.30	0.20
Fe	0.04	0.02	0.02
Mn	0.009	0.003	0.002
Zn	0.004	0.003	0.002
Cu	0.001	0.0007	0.0005

Table 3: Effect of "marejea" hay supplementation on nutrient intake and apparent digestion coefficients of the rations.

Parameters	rations
	T1	T2	T3	T4
Number of animal	3	3	3	3
Mean weights (kg)	21.5	26.1	24.1	24.5
Mean weight (kg W0.75)	9.25	11.2	10.4	10.5
Daily intake (g/day)
Dry matter	412.8a	487.3b	491.7b	510.2b
Dry matter (g/kg W0.75)	49.5a	58.5b	59.0b	61.2b
Crude protein	18.2a	40.5b	58.7b	120.5b
Crude protein (k/kg W0.75)	2.2a	4.7a	7.0b	14.5c
Digestibility coefficients
Dry matter	50.7a	56.6a	56.2a	64.3b
Crude protein	22.1a	48.3b	55.7b	62.4c
Crude fibre	59.8	58.2	57.3	51.2
Organic matter	57.1a	57.6a	58.2a	66.6b

abc = means in same row with different superscripts are significantly different (P<0.05)

Intake and digestibility study

Results on intake and apparent digestibility are given in Table 3. The total dry matter intake (DMI) increased with increased supplementation of "marejea" While there was a significant difference (P<0.05) between the unsupplemented and the supplemented diets, there was no significant difference (P<0.01) among the supplemented diets.

Kitaly (1982), and Mero (1985) observed an increase in DMI when Rhodes grass was supplemented with increasing levels of protein supplement. The increasing level of "marejea" resulted in a decline in the hay intake as observed in the growth study. Robles et al (1981) reported that as the fibre content in the diet decreased DMI increased because the animals increased intake when the quality of the leaf is high. Dietary protein supplementation is known to improve intake by increasing the supply of N to the rumen microbes. This has a positive effect of increasing microbe population and efficiency thus enabling them to increase the rate of breakdown of the digesta. As the rate of breakdown and passage of the digesta increases, feed intake is accordingly increased (Van Soest, 1982). The crude protein intake (CPI) and organic matter intake (OMI) increased with increasing "marejea" supplementation.

The results have shown that dry matter digestibility (DMD) increased with increasing level of "marejea" supplementation but only significantly in T₄. Several workers have reported that the DMD improves when a roughage is supplemented with a legume or concentrates (Elliot and Topps, 1963; Minson and Milford, 1967; Gordon 1979; Butterworth, 1985). The crude protein digestibility (CPD) and organic matter digestibility (OMD) increased with increasing level of "marejea" supplementation. These results compare favourably with those reported by El Haq (1976), Kitaly (1982) and Massae (1984) and others who observed increases in CPD and OMD with increased supplementation of protein. However, the crude fibre digestibility (CFD) decreased with increased supplementation. The low CFD observed in this study could be due to increased DMI brought about by increased CP contents. Increased DMI could lead to increased rate of passage of digesta hence less time for rumen microorganisms to digest the crude fibre.

Growth study

Results of feed intake and growth performance of the sheep used in the growth experiment are given in Table 4 and 5 respectively. The total DMI (g/day and g kg W^0.75) were observed to take the same trend as those observed in the digestibility study. The DMI, CPI and OMI increased level of "marejea" supplementation. Elliot (1967) and Orskov et al (1971) observed similar trends with cattle and sheep supplemented with different levels of protein.

Both the total weight gain and daily gain increased with the level of "marejea" supplementation. Total weight gain was significantly different (P<0.05) between the unsupplemented group and the supplemented. The growth rate increased from 34.2 g/day for the unsupplemented group to 69.1 g/day for the sheep fed "marejea" ad libitum. The daily gain of 509 for the unsupplemented Black Head Persian sheep has been reported by Nyaki (1981) using Rhodes grass hay as a basal diet. The big difference observed with this study could be due to the high crude protein content of the pasture grazed. Nyaki's experiment was conducted during the short rains and extended to the onset of long rains in march.

Nitrogen balance

Nitrogen intake, excretion and retention increased significantly (P<0.05) with increased level of supplementation (Table 6). This is in accordance with the findings of Akinsoyinu (1974); Reynolds, (1981); Kitaly, (1982); and Massae, (1984). Unsupplemented animals were in negative nitrogen balance indicating that the nitrogen content of mature Rhodes grass hay is not sufficient for maintenance needs of sheep. It is thus necessary to supply protein supplements when feeding such low quality roughages as suggested by Gihad (1976) and Reynolds (1981).

Table 4: Effect of "marejea" hay supplementation on nutrient intake in the growth study

Parameters	Rations
	T1	T2	T3	T4
Number of animals	3	3	3	3
Dry matter intake (DMI g/day)
Rhodes grass	172.6a	160.4a	100.2a	100.6b
"Marejea"	-	75.4a	140.8b	152.9b
Total	176.6a	235.8b	240.2b	253.5b
Intake g/kw W0.75	56.9a	27.6b	79.3b	83.6b
Organic matter intake (OMI) g/day	160.3a	226.4b	212.1b	230.5b
g/kg W0.75	20.4a	27.6b	28.2b	30.4b
Crude protein intake (CPI) g/day	10.2a	26.5b	35.6c	40.6c
g/kg W0.75	1.34a	3.4b	4.6c	5.3c

abc = means in same rows with different superscripts are significantly different (P<0.05)

Table 5: Effect of "marejea" hay supplementation on the growth performance of sheep

Parameters	Rations
	P1	2	3	4
Number of animals	4	4	4	4
Initial liveweight (kg)	23.5	24.0	21.5	22.4
Final liveweight (kg)	26.6	27.8	27.2	28.6
Mean liveweight (kg)	25.1	25.9	24.35	25.5
Total weight gain (kg)	3.1a	4.8b	5.7b	6.2b
Growth rate (g/day)	34.2a	42.4b	63.7c	69.1c

abc = Means in same rows with different superscripts are significantly different (P<0.05)

Table 6: Effect of "marejea" hay supplementation on nitrogen utilisation

Parameters	Rations
	T1	T2	T3	T4
Number of Animals	3	3	3	3
Nitrogen intake g/day	3.1a	5.6b	11.3c	18.4d
g/kg W0.75	0.3a	0.5a	1.3b	1.8b
Nitrogen Excretion (g)
Faecal	2.2a	3.3a	4.7b	8.3c
Urine	1.1a	1.8a	2.5b	4.9c
Total	3.3a	5.1a	7.26b	13.2c
Nitrogen retained
g/day	-0.2a	0.4b	4.04c	5.2c
g/kw W0.75	-0.03a	0.04a	0.11a	0.35c
% of N - intake	- 6.4a	8.2b	35.7c	28.4c
% of N-digested	-29.4	14.8	64.2	72.3

abc = Means in same rows with different superscripts are significantly different (P<0.05)

Conclusions

From the results obtained it can be concluded that "marejea" hay improved DMI, CPI and OMI of low quality rhodes grass hay, resulting in increased daily gain and total weight gain. It could therefore be used as a cheap alternative protein supplement for small livestock keepers in the rural areas which have little or no access to conventional protein supplements.

Acknowledgements

The authors would like to thank PANESA (Pasture Network for Eastern and Southern Africa) for the financial support which enabled this study to be carried out.

References

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