Rumen degradation of dry matter and organic matter of different parts of the banana plant

Rumen degradation of dry matter and organic matter of different parts of the banana plant

This paper reports the preliminary evaluation of the nutritive value of different parts of three varieties of banana plant, using the nylon bag technique.

Five parts of the banana plant (leaf lamina, leaf mid-rib, pseudo-stem sheath, pseudo-stem core and fruit peelings) from three varieties (Bukoba, Mtwike and Pazz) were analyzed for their dry matter and organic matter degradability in the rumen of sheep at different incubation times.

The mean values for disappearance at 48 hours incubation were 27.7, 37.4, 45.4, 59.2 and 60.6% units for DM and 25.7, 35.4, 43.5, 56.7 and 58.6% units for OM in leaf lamina, leaf mid-rib, pseudo-stem sheath, pseudo-stem core and fruit peelings respectively. Different varieties showed some difference in the degradability of different parts after 48 hours of incubation. Bukoba had lower leaf-lamina, leaf-mid-rib and pseudo-stem sheath degradability than the other varieties whilst Mtwike had higher degradability of all parts except pseudo-stem sheath which was lower than that of Pazz.

It was concluded that banana pseudo-stem has a greater potential than the leaf tissue as the basal diet for ruminants and that the fruit peelings are the most digestible of the residues.

Smallholder dairy farmers in the Northern part of Tanzania, mainly Kilimanjaro and the highlands in the Arusha region, practice a cut-and-carry system of animal husbandry, due to scarcity of land for grazing. Most of the land in these two regions is used for two cash crops: coffee and banana, the latter being the staple food crop.

The farmers rely on crop residues as the main feed for their animals. The leaves and pseudo-stems of the banana plant form the basal diet, along with small amounts of green grass such as Guatemala, Napier and Setaria grown on the boundaries of the plots (Mrawa 1987). Maize stover and bean haulms are other crop residues which are fed.

The banana has a high yield of total biomass. Ffoulkes et al (1978) reported a maximum residual biomass (pseudo-stem and leaves) of 13 to 20 tonnes DM/ha in a year. It has also been indicated that removal of the fully expanded lower banana leaves during 8 to 12 occasions during the life of the plant does not affect fruit yield (Meyreles and Preston 1979). This implies that banana leaves can be used throughout the year as animal feed.

There is paucity of information on the nutritive value of fibrous banana residues. Espejo et al (1978) fed 200 kg steers a mixture of 80% pseudo-stem and 20% leaves (including the petiole)(fresh matter basis) with added urea, ammonium sulphate and minerals, and reported an apparent dry matter digestibility of 70"2% and voluntary intakes of 2.1"0.03 kg dry matter per 100 kg liveweight. Rumen fermentation studies on these same animals (Ravelo and Hovell 1978) showed that rumen ammonia levels increased from 53 mg/litre before feeding to 140 mg/litre two hours afterwards; corresponding values for molar proportions of the VFA (acetate, propionate and butyrate) were 54, 34, 9 and 51, 31, 16. The rumen liquid turnover rate was 0.86 and the flow 0.93 litres/h.

Ffoulkes and Preston (1978) measured in vivo digestibilities and intakes by steers of combinations of leaves and pseudo-stem ranging from 100:0 through to 0:100% (fresh basis). Digestibility increased and voluntary intake decreased as the proportion of pseudo-stem in the mixture increased. Using the in situ rumen nylon bag technique, Santana and Hovell (1979) reported that the pseudo-stem was more rapidly degraded than the leaves.

The present work was designed to investigate further the nutritive value of the different parts of the banana plant using material from 3 varieties commonly used in Tanzania.

Two healthy male Black-head Persian sheep fitted with permanent rumen cannulas of 40mm diameter were used. They were fed Chloris gayana hay ad libitum as the basal diet, supplemented with 500 g/d of a mixture of maize bran, cotton seed cake and minerals in the ratio of 66: 33: 1 respectively.

Three varieties of mature bananas (Bukoba, Mtwike and Pazz) were used. After harvesting the fruit, the leaf lamina, leaf midrib, pseudo-stem sheath and pseudo-stem core were separated from the plant using a knife.

The different parts were chopped, air dried and then ground using a hammer mill with 0.25 mm screen size. Samples of the fresh material were dried in an oven at 60 °C to a constant weight to determine DM content.

Rumen degradabilities were measured using the technique described by Orskov et al (1980). Two grammes of the air dried samples were weighed into labelled weighed nylon bags (80 mm x 20 mm; pore size of 0.052 mm). At the same time 2 g samples were weighed into crucibles and dried in an oven for 48h at 60 °C to obtain the DM of the sample. These were ashed at 550 °C for 5h to determine the organic matter (OM).

The bags were tied firmly using nylon strings and they were anchored with about 25 cm of nylon thread in the rumen of each sheep in duplicate for each sample and for each incubation time. The incubation times were 6, 12, 18, 24, 48 and 72h. The bags containing undigested residues were removed from the rumen after each incubation time and thoroughly washed in running tap water until the washing water was clear. They were then dried at 60 °C for 48h, cooled in a desiccator and their weight taken.

The dried residues were transferred from the bags into weighed labelled crucibles and weighed. The samples were re-dried for 24h at 60 °C and weighed. They were ashed at 550 °C for 5h.

Water solubility of the samples was measured by incubating triplicate samples in water at room temperature for 2 hrs. They were then processed in a similar manner as those from the rumen.

The mean values for DM degradability of the different banana parts from the three varieties after 24 and 48h incubation are shown in Tables 1 and 2 respectively. Organic matter degradability of different parts at 48h incubation are shown in Table 3.

Table 1: Dry matter disappearance (%) of different banana parts from three varieties after 24h incubation in the rumen

	Variety
Banana parts	Mtwike	Pazz	Bukoba	Mean

Leaf lamina	24.5	17.4	16.9	19.6
Leaf mid-rib	31.2	28.5	30.0	29.9
Pseudo-stem sheath	34.0	36.9	37.3	36.1
Pseudo-stem core	44.2	47.1	52.1	47.8
Fruit peelings	54.8	48.0	49.6	50.8
Mean	37.7	35.6	37.2	36.8

Table 2: Dry matter disappearance (%) of different banana parts from three varieties after 48h incubation in the rumen

	Variety
Banana parts	Mtwike	Pazz	Bukoba	Mean

Leaf lamina	30.3a	30.2a	22.5b	27.7
Leaf mid rib	43.8a	39.1b	29.3c	37.4
Pseudo-stem sheath	45.7a	49.6b	41.0c	45.4
Pseudo-stem core	60.3a	57.0b	60.3a	59.2
Fruit peelings	63.0a	59.1b	59.0b	60.5
Mean	47.7a	47.9a	42.4b	46.0

abc - means within row with different subscripts differ significantly (P< 0.05) from each other.

Table 3: Organic matter disappearance (%) of different banana parts from three varieties after 48h incubation in the rumen

	Variety
Banana parts	Mtwike	Pazz	Bukoba	Mean

Leaf lamina	28.6a	28.5a	20.1b	25.6
Leaf mid-rib	42.6a	35.7b	27.9c	35.4
Pseudo-stem sheath	44.1a	47.8b	38.7c	43.5
Pseudo-stem core	58.4a	54.8b	56.8a	56.7
Fruit peelings	61.8a	57.1b	56.9b	58.6
Mean	47.1	44.8	40.1

abc - Means within row with different subscripts differ significantly (P< 0.05) from each other.

There were no differences between varieties after 24h of incubation but there were between different components of the plant, with lowest values recorded for the leaf lamina.

After 48h of incubation (Table 2) there was a significant difference (P< 0.05) between varieties in the DM degradability of the different banana parts. Bukoba variety had lower degradability of leaf lamina, leaf midrib and pseudo-stem sheath than the other two varieties. Mtwike variety had significantly higher (P< 0.05) degradability of all parts studied except pseudo-stem sheath which was lower than that of Pazz. Mean degradability values of the different parts from the three varieties showed that leaf lamina had the lowest degradability of DM at 48h incubation whilst fruit peelings had the highest values.

The DM disappearance rates at different incubation times (Table 4) shows that fruit peelings had the highest dry matter and organic matter disappearance values followed by pseudo-stem core, pseudo-stem sheath, leaf mid rib while the leaf lamina had the lowest values at all incubation times. The differences in DM disappearance between the different banana parts were significant (P< 0.05) at all incubation times except at 6h.

Table 4: Dry matter disappearance (%) of different banana parts for different times of incubation in the rumen


	Incubation time (hr)

Banana parts	6	12	24	48	72

Leaf lamina	6	10	13	27	31
Leaf mid-rib	7	15	22	37	43
Pseudo-stem sheath	8	22	29	55	52
Pseudo-stem core	15	26	40	59	63
Fruit peelings	10	28	45	62	65
Approximate SE means			?3

The significant differences in the dry matter degradability of the different parts of the banana plant (Tables 1 and 2) from different varieties suggest that when feeding bananas to animals both the part of the plant and the variety should be taken into consideration. In the present experiment it is obvious that the Bukoba variety was poorer in nutritive value than Mtwike and Pazz.

The observed differences between banana parts in both DM and OM degradability confirm earlier preliminary reports in the literature that leaf tissue is less rapidly degradable (is of lower digestibility) than tissue from the pseudo-stem (Santana and Hovell 1979). The relatively high tannin content in banana leaves is another factor which could depress their digestibility in the rumen (Egum 1987).

The superior values for stem, as opposed to leaf material, is contrary to results with most other plants and presumably is due to the anatomical and physiological features of the pseudo-stem in which erectness is achieved by the way in which water is held in the cells, and not by the presence of high levels of lignin in the cell wall.

The DM and OM degradability values at 48h of incubation are the most important as this period is closer to the mean retention time of 48h for fibrous feeds in the rumen. Thus the 48h degradation values could be taken as indicative of in vivo digestibility coefficients for the different components.

The reported data, indicating 48h degradabilities in excess of 50%, substantiate: the observed growth rates of 500 g/day in young crossbred Jersey steers in Seychelles fed chopped banana leaf and pseudo-stem residues supplemented with urea/molasses and leucaena foliage (Preston and Leng 1987); and traditional farmer practice in Tanzania of using the fibrous residues from the banana plant as components of livestock feeding systems.

The present study has confirmed the potential high feeding value of fibrous banana residues, especially the fruit peelings and the core of the pseudo-stem, and the lower potential digestibility of the leaves.

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