The use of Leucaena leucocephala supplementation to improve the utilisation of maize stover by sheep

A E Kimambo, A M Makiwa and MN Shem

Department of Animal Science and Production
Faculty of Agriculture
Sokoine University of Agriculture
PO Box 3004, Chuo Kikuu, Morogoro, Tanzania

ABSTRACT

Experiments were conducted to investigate the effect of Leucaena leucocephala supplementation on the intake and rumen degradation of maize stover (Staha variety) by sheep. A feed intake study on four levels of Leucaena supplementation (0, 3, 6 and 9 g dry matter/kg liveweight per day) in a 4 x 4 Latin square design was undertaken. Dry-matter degradation of maize stover and rumen ammonia concentration were measured using two fistulated sheep fed the four diets.

Total dry-matter intake of the supplemented diets was significantly (P<0.05) higher than that of the unsupplemented diet. Daily dry-matter intake of maize stover alone increased from 32.8 g/kg for the unsupplemented diet to 36.2 g/kg for the diet containing the lowest level of Leucaena supplementation. Higher levels of Leucaena supplementation led to a decrease in the amount of maize stover consumed.

Leucaena supplementation significantly (P<0.05) increased the rumen degradation of maize stover at 48 hours of incubation compared to unsupplemented maize stover.

Ammonia concentration in the rumen increased significantly (P<0.05) with increase in the level of Leucaena supplementation up to 6 g/kg per day. Higher levels of Leucaena in the diet did not result in further increase in rumen ammonia concentration. There was no change in the rumen pH for the different levels of Leucaena supplementation.

The results indicate that intake and rumen degradation of maize stover in sheep could be improved by supplementing the animals with up to 6 g DM/kg liveweight per day of Leucaena hay. Higher levels of supplementation appear to lead to substitution effects.

RESUME

Amélioration de l'utilisation de la paille de maïs par les ovins grâce à une complémentation de Leucaena leucocephala

Des expériences ont été menées sur des ovins pour déterminer l'effet d'une complémentation de Leucaena leucocephala sur la consommation et la dégradation de la paille de mais (variété Staha) dans le rumen. L'ingestion a été étudiée avec quatre niveaux de complémentation de Leucaena (0, 3, 6 et 9 g de matière sèche par kilo de poids vif et par jour) sur le modèle d'un carré latin d'ordre 4. La dégradation de la matière sèche de la paille de mais et la concentration de l'ammoniac dans le rumen ont été mesurés sur deux ovins fistulés alimentés avec les quatre rations.

L'ingestion totale de matière sèche était significativement plus élevée (P<0,05) avec la complémentation. En ce qui concerne la paille du seul maïs, la consommation journalière de matière sèche avait augmenté de 32,8 g/kg/j pour la ration non complémentée à 36,2 g/kg/j pour la ration complémentée contenant le niveau le plus faible de Leucaena. Des niveaux plus élevés de complémentation entraînaient une baisse de la consommation de paille de mais.

Par rapport à la ration non complémentée, l'apport de Leucaena entraînait un accroissement significatif (P<0,05) de la dégradation de la paille dans le rumen après 48 heures d'incubation. La concentration d'ammoniac dans le rumen augmentait significativement (P<0,05) avec l'accroissement du niveau de Leucaena dans la ration et ce, jusqu'à 6 g/kg/j. Au-delà, l'augmentation du niveau de complémentation n'entraînait plus aucun accroissement de la concentration d'ammoniac dans le rumen. Le pH du rumen était indépendant du niveau de complémentation de la ration.

Ces résultats montrent que l'on peut accroître la consommation de paille de mais et sa dégradation dans le rumen des ovins en les soumettant à une ration complémentée avec jusqu'à 6 g de matière sèche de foin de Leucaena par kilo de poids vif par jour. Des niveaux plus élevés entraînent des phénomènes de substitution.

INTRODUCTION

Intake of straws and stover by ruminants is usually too low to maintain body weight: tough texture, poor digestibility and nutrient deficiency all contribute to the low level of consumption (El-Naga, 1989). These roughages are low in readily available energy, carbohydrates and nitrogen, which reduces the efficiency with which they are utilised by animals. Chemical treatment of straws using sodium hydroxide (Urio, 1977; Kategile, 1979) or urea (Kiangi 1981; Raymond, 1989) can improve both their digestibility and intake, but is not always practical under farmer conditions. Thus alternative strategies to improve straw utilisation have been sought.

Leguminous forages such as Leucaena leucocephala have been used to improve dry-matter intake and digestibility of pasture hay by sheep (Bamualim et al, 1984). Because of the increased interest in the use of Leucaena spp as protein supplements for ruminants, the present study investigated the effect of various levels of Leucaena leucocephala supplementation on the intake and rumen degradation of maize stover by sheep.

MATERIALS AND METHODS

Experimental animals and feeds

Six Blackhead Persian sheep were used in the experiment. Four sheep, weighing about 28 kg, were used for intake studies in a 4 x 4 Latin square. The other two, weighing 33 kg and 41 kg, were fistulated and used for degradation studies.

Maize stover was obtained from harvested maize fields and chopped into 3-5 cm lengths. Leucaena leucocephala hay was obtained by cutting and wilting leafy branches of the plant and threshing the branches to separate the leaflets (the hay) from the twigs.

Intake studies

For the intake studies, the animals were confined in individual metabolic cages and offered a known quantity of maize stover ad libitum twice a day at 0900 and 1600 hours. Each animal also received 200 g of maize bran and vitamin/mineral mixture, alone or together with one of three levels of Leucaena hay supplement (3, 6 and 9 g dry matter/kg liveweight per day), at the morning feeding. Each diet combination was fed to each animal for 14 days, a seven-day preliminary period and a seven-day data collection period.

Degradability of maize stover

Degradation of maize stover was investigated for each diet combination using the nylon-bag technique (Ørskov et al, 1980).

Maize stover was ground to pass through a 2.5-mm screen and 2-g samples were weighed into 20 labelled nylon bags of known weight. For each ration, 10 bags were put into the rumen of each sheep and removed, two at a time, after 6, 12, 24, 48 and 72 hours of incubation. The removed bags were washed under running tap water until the water was clear and the residues were dried in an oven at 60°C for 48 hours, cooled in a desiccator and weighed. Dry-matter degradability was calculated using the formula

Rumen ammonia and pH

For rumen ammonia and pH determination, rumen liquor was obtained from the fistulated animals during the data collection period for each level of Leucaena supplementation. The liquor was collected at 0600, 1000, 1400 and 1800 hours, strained through cheese-cloth and centrifuged at 3000 rpm for 15 minutes, and 20-ml samples were taken for immediate pH determination.

For ammonia determination, 25-ml samples of the centrifuged rumen liquor were treated with two drops of concentrated sulphuric acid and frozen to await analysis. For the analysis, 5 ml of rumen liquor were mixed with 10 ml of 5% sodium tetraborate solution. Two drops of mixed indicator were added and the mixture was distilled using the kjeltec system. The distillate was collected in a flask containing 25 ml of 20% boric acid, and titrated with 0.1213N HCl. Ammonia concentration was calculated by

% Ammonia = Ammonia-N x 1.21

% Ammonia was then converted into mg ammonia/litre.

Statistical analysis

Two-way analysis of variance for a Latin square design was used for intake studies data, and one-way analysis of variance was used for other parameters, according to Snedecor and Cochran (1980). The significance of the results was tested using F test and LSD.

RESULTS

Dry-matter intakes (DMI) of the total ration roughage (maize stover plus Leucaena) and of maize stover alone are shown in Table 1.

Total DMI was significantly (P<0.05) increased by Leucaena supplementation. Total DMI of ration B was significantly lower (P<0.05) than that of ration D, but there was no significant difference between the DMI of rations B and C or rations C and D.

Dry-matter intake of maize stover alone increased when the diet was supplemented with 3 g Leucaena DM/kg liveweight per day, but further increase in the level Leucaena supplementation led to a decline in the amount of maize stover consumed.

Dry-matter (D M) and organic -matter (OM) de gradabilities of maize stover in the rumen of sheep fed the different rations are shown in Table 2. Leucaena supplementation increased DM and OM degradability of maize stover at all incubation times. The greatest increase was observed at the supplementation level of 3 g Leucaena DM/kg liveweight per day. Statistical analysis of the DM and OM degradabilities at 48 hours of incubation revealed that ration A had significantly (P<0.05) lower DM and OM degradability than the supplemented rations. Ration B had lower (P<0.05) DM and OM degradabilities than ration D, but the differences between rations B and C or rations C and D were not significant (P>0.05).

Table 1. Dry-matter intake of total roughage (maize stover and Leucaena supplement) and maize stover alone for the four rations

Ration A = unsupplemented
Ration B = supplemented with 3 g Leucaena DM/kg liveweight per day
Ration C = supplemented with 6 g Leucaena DM/kg liveweight per day
Ration D = supplemented with 9 g Leucaena DM/kg liveweight per day

Table 2. Dry-matter and organic-matter degradabilities of maize stover at different incubation times

Ration A = unsupplemented
Ration B = supplemented with 3 g Leucaena DM/kg liveweight per day
Ration C = supplemented with 6 g Leucaena DM/kg liveweight per day
Ration D = supplemented with 9 g Leucaena DM/kg liveweight per day

Rumen ammonia concentrations in sheep fed the four rations are shown in Table 3. Inclusion of Leucaena in the maize-stover-based diet significantly (P<0.05) increased the rumen ammonia concentration. The concentration in sheep fed ration B was significantly (P<0.05) lower than those in sheep fed rations C and D, which were not different (P>0.05) from each other.

Rumen ammonia concentration increased immediately after feeding, and then decreased (Figure 1).

Rumen pH was not affected (P>0.05) by ration (Table 3).

DISCUSSION

The high dry-matter intake of rations supplemented with Leucaena indicates that Leucaena is a good supplement to low quality roughages such as maize stover. This improvement in intake with Leucaena supplementation is in agreement with results reported by Bamualim et al (1984). However, Dixon et al (1981) cautioned that an increase in total dry-matter intake could be due to consumption of the supplement per se rather than the roughage.

The fact that the highest dry-matter intake of maize stover was obtained at a supplementation level of 3 g Leucaena DM/kg liveweight per day may indicate that it is this optimum level of supplementation for poor quality roughages. Further increase in the level of Leucaena supplementation led to a substitution effect whereby the intake of maize stover was reduced. Increase in the intake of maize stover with Leucaena supplementation could be due to the increase in the concentration of rumen ammonia and dry-matter degradability of maize stover.

The improvement in the rumen degradation of maize stover dry matter and organic matter with Leucaena supplementation indicates a possible improvement in microbial growth. This is supported by the observed increase in rumen ammonia concentration.

Table 3. Rumen ammonia concentration and rumen pH for the four rations

Ration A = unsupplemented
Ration B = supplemented with 3 g Leucaena DM/kg liveweight per day
Ration C = supplemented with 6 g Leucaena DM/kg liveweight per day
Ration D = supplemented with 9 g Leucaena DM/kg liveweight per day

Figure 1. Rumen ammonia concentration before and after feeding the four rations

Rumen ammonia concentration is an indicator of nitrogen available for microbial protein synthesis. In this study, rumen ammonia concentration increased from 32 mg/litre for the unsupplemented diet to about 90 mg/litre for higher levels of Leucaena supplementation. FAO (1986) reported that, for efficient rumen function, ammonia concentration in the rumen should be between 50 and 90 mg/litre. With the unsupplemented maize stover diet, the rumen ammonia concentration was below the critical level, and this corresponds with the low dry-matter intake and dry-matter and organic-matter degradabilities for that ration.

CONCLUSIONS AND RECOMMENDATIONS

Dry-matter intake, rumen degradation and rumen ammonia concentration all showed improvement when the maize stover diet was supplemented with Leucaena leucocephala. This means that the efficiency of utilisation of maize stover is improved by Leucaena inclusion. However, the improvement declined at higher levels of Leucaena supplementation. It is therefore recommended to supplement maize stover with Leucaena at a level not exceeding 6 g DM/kg liveweight per day.

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