The potential of browse plants in the nutrition of small ruminants in the humid forest and derived savanna zones of Nigeria*

B.A.R. Carew, A.K: Mosi, A.U. MBA and G.N. Egbunike

Materials and methods

Palatability trial

The zones

1. Lowland forest belt

2. Derived savanna

Results and discussion

Palatability trial

Literature cited

Materials and methods

A preliminary assessment of the level of household supplementation of sheep and goat diets was carried out in three villages each in the humid forest and derived savanna zones of the Oyo State in Nigeria. Each of the selected villages held between 120-200 small ruminants. Two sheep (average weight 25 kg) and two goats (average weight 20 kg) on a low plane of supplementation and a similar number on a medium plane, were selected from each village and zone for observation.

Using a pair of binoculars, each animal in a village was observed by a trained assistant at 10-minute intervals, within the period of 07.00 and 19.00 hours in a six-weekly cycle. Thus 12 paired observations, spread within time and location, were made on 12 sheep and 12 goats per zone in the late rainy season of the year (July–September 1979). The observed animals were recorded for time spent foraging, ruminating, idling and scavenging. Samples of browse plants, forbs and grasses selected during the day were collected for botanical and chemical analysis, and they were then ranked according to the mean frequency of bites and time spent feeding on them.

Palatability trial

Following the first few weeks of the village observations, six of the more commonly selected herbages were fed fresh in a cafeteria system together with a grass to four sheep and four goats (Table 1). A period of 7 days was allowed for adaptation to confinement during which the test herbages were randomly fed ad lib. Thereafter, measured quantities of the test herbages that could provide a 10% weighback were fed twice (8 am and 3 pm) daily for 21 days. Water and cobalt iodized salts were also available ad lib. Samples of feed offered and leftovers were collected daily, bulked weekly, and subsampled for proximate analysis (AOAC, 1965) and in vitro organic matter digestibility determination (Tilley and Terry, 1963, as modified by Alexander and McGowan, 1961 and 1966). (Table 4).

The zones

1. Lowland forest belt

The forest belt stretches approximately 60-120 km along most of the West African coast from Sierra Leone eastwards and includes the humid forest and mangrove swamps (Crowder and Chedda, 1974). Active tree and food crop farms are scattered all over the land and these are interspersed with bush fallows of varying sizes. Tall coarse grasses such as Pennisetum, Hyparrhenia, Andropogon, Cenchrus and Aristida invade cultivated areas and natural clearings but grass cover is sparse or absent under the tree cover (Crowder and Chedda 1974).

2. Derived savanna

The derived savanna occupies a narrow belt adjacent and north of the lowland forest (Hopkins, 1965; Nye and Greenland, 1960; Rose-Innes, 1971). Tall coarse grasses (Hyparrhenia, Andropogon) cover fallow farmlands. During the 3–4 months of dry season, the under-utilized, tall, parched grasses provide most of the combustible materials that are annually burnt to clear the land and to harvest game. These regular fires have destroyed many tall trees except fire-resistant gnarled shrubs and bushes not exceeding 10m high. Reduction of the frequency of burning causes an invasion of woody species and rapid reversion to forest (Rose-Innes, 1971).

Results and discussion

The results in this report represent some of the findings in the first quarter of an ongoing project in the forest and savanna belts of southern Nigeria on the utilization of browse plants by goats and sheep in the village setting.

Table 2 shows the distribution of the attributes of their behaviour which in this report are classified as rumination, idling, scavenging and foraging (browsing and grazing). Attempts were also made during the experimental period to assess supplementary feed dry matter intakes per animal per day in both zones. Table 1 shows the average amount of supplemental feed (DM) per animal/day. The main supplements were cassava peels and milled maize chaff in the savanna and forest zones respectively.

Table 1. Daily dry matter intake of goats and sheep stall fed with six browse species and panicum maximum

Table 2. Behaviour distribution of small ruminants in the village setting of southern Nigeria

Dry matter intake from supplementary feeds per kg liveweight per animal per day for the forest goats and sheep was calculated to be about 850g (4.24%) and 7608 (3.04%) respectively, comparable figures for the savanna being 360g (1.81%) and 510g (2.05%). Thus the forest animals appeared to be better supplemented than their savanna counterparts. This observation could be more associated with the farming systems and practices of the villages investigated than with their climatic differences. The data also indicates that between zones and within species the higher the level of DM supplementation the lower the time spent in browsing and grazing (Table 2). Thus in the forest zone where supplementation is higher for both goats and sheep the times spent foraging are lower than the figures for the same species in the savanna zone.

Figures as shown in Table 2 indicate that between zones and within species increased utilization of the forage reduces scavenging (inverse relationship). Thus the savanna goats and sheep which browsed and grazed longer (20.63% and 30.19% respectively) spend less time scavenging (8.13% and 9.14% respectively). Thus scavenging, in both species, appeared to argument foraging which in turn depended on the amount of supplementary feed offered.

Time spent by sheep and goats in browsing and grazing in the study is tabulated in Table 3 and graphically expressed in Figure 1. The biting ratios of browse to grass in the forest zone were: 77:1 for the goats and 13:1 for the sheep. Comparable figures for the savanna zone were: goats 1.1:1 and sheep 1.6:1. Thus browse plants are selected more often by goats and sheep in the forest zone than in the savanna region, though browse plant height or accessibility tended to affect selection pattern.

Table 3. Grazing browsing time of small ruminants in southern Nigeria

Goats and sheep in the savanna zone respectively spent 52.2% (1.29 hours) and 61.1% (2.20 hours) in browsing and 47.8% (1.18 hours) and 38.9% (1.40 hours) in grazing. Comparable feeding time allocations for the forest zone sheep and goats were respectively 98.7% (0.77 hours) and 92.6% (2.24 hours) for browsing, while the remainder of 1.3% (0.01 hours) and 7.43% (0.18 hours) were spent grazing.

Figure 2 shows the distribution of eating intensity between 0.700-10.00 hours in the study areas. Goats in both zones appeared to have a two-peaked eating time pattern, the intensity being high around late morning and higher during the evening. On the other hand eating time for the sheep appeared to be one-peaked, the intensity increasing towards the afternoon.

Palatability trial

Table 1 shows the daily dry matter intake of the experimental dwarf goats and sheep, stall-fed with six browse species and a grass (Panicum maximum). Average daily dry matter intake for the sheep was 1805.91g with a comparable figures of 1330.00g for the goats. The intake per kilogram of metabolic size (Wkg 0.75) for the sheep was 223.45g/day as compared to 167.18g/ day for the goats. The mean daily dry matter intake as a percentage of the mean liveweight was 11.20% for the sheep and 8.32% for the goats. The intake figure for the goats compared favourably with the 8% observed by French (1970). Majundar (1967) quoting data from Brody's experiments of 1938 concludes that the minimum appetite of the goat for DM is about 5% of the body weight and with well-bred goats intake could be as high as 8 1/2% of the body weight.

During the 21-day experimental period both goats and sheep appeared to concentrate their choice on Spondias mombin and Cyclicodiscus gabunensis, being closely followed by Ficus exersperata. The mean percentage intake of Spondias mombin in the total daily DM intake of the goats was 29.80% (396.37g) as compared to 27.05% (488.2kg) for the sheep. For Cyclicodiscus gabunensis comparable figures were 38.19% (507.9kg) and 26.06% (470.48g) respectively. Intake of Panicum maximum was poor and constituted only 9.29% (68.37g) total DM intake of the sheep with a comparable figure of 6.56% (87.43g) for goats. The sheep gained an average of 120g/day and the goats 90g/day. The high weight gains and daily DM intake could be a response to the free choice of plants that are hitherto not too accessible to foraging animals under the traditional methods of management. Most of these shrubs and trees often grow out of reach of the animals. However the fact is established that some of the offered browse plants which incidentally retain most of their leaves through the dry season are more acceptable and perhaps more complete feeds to goats and sheep than the sown Panicum maximum—pastures.

Figure 1. Grass browse utilization by goats and sheep in southern Nigeria.

Table 4 shows the proximate composition, organic matter% dry matter%, silica free ash, acid detergent fibre and the in vitro organic matter digestibility coefficient of the test forages. Differences in the crude protein content were small and could not probably direct the pattern of choice between the offered forages. In fact Asphilia Africana which is one of the least preferred had the highest protein content of 17.17% as compared to 14.01% for Spondias mombin and 15.80% for Cyclicodiscus gabunensis which are the most acceptable to both species of ruminants used in the experiments. Panicum maximum which is not favoured in the palatability trial also had the lowest protein content of 12.76%.

Table 4 Proximate composition, dry matter, organic matter, acid detergent fibre and the in vitro organic matter digestibility coefficient of the test forages

	Total ash %	Ether extract %	Crude protein %	Crude fibre %	NFE %	Silica %	Silica free ash %	DM %	OM %	ADF %	In vitro OM Dig. %
Ficus exersperata	12.00	10.00	14.45	25.00	38.55	10.00	2.00	54.00	88.00	20.00	45.51
Newboulotia leavis	7.00	900	16.14	29.00	38.86	4.00	3.00	60.00	93.00	37.00	41.84
Asphilia africana	13.00	16.00	17.17	25.00	26.83	5.00	8.00	77.00	85.00	26.00	45.45
Spondias mombin	6.00	7.00	14.01	17.00	55.99	4.00	2.00	56.00	94.00	24.00	37.50
Cyclicodiscus gabunensis	5.00	8.00	15.80	21.00	50.20	3.00	2.00	68.00	95.00	23.00	54.00
Ficus (sp)	7.00	5.00	14.83	22.00	51.17	4.00	3.00	73.00	93.00	25.00	41.49
Panicum maximum	13.00	10.00	12.76	30.00	34.24	10.00	3.00	78.00	87.00	28.00	36.96.

The acid detergent fibre and crude fibre content appeared to correlate more with free choice pattern than crude protein. Newbouldia leavis and Panicum maximum which are the least palatable had the highest ADF values of 37.0% and 28% respectively. Comparable figures for the two most palatable forages, Spondias mombin and Cyclicodiscus gabunensis, being the lowest values of 24% and 23% respectively.

Crude fibre content for the least palatable forages, Newbouldia leavis and Panicum maximum, also had the highest values of 29.0% and 30.0% respectively; comparable figures for Spondias mombin and Cyclicodiscus gabunensis being 17.0% and 21.0% respectively. The relationship of the organic matter in vitro digestibility coefficient with choice was no more consistent than the earlier ones discussed.

Theoretically one expects some measure of relationship between chemical composition of forages and their preference but this experiment does not seem to highlight a consistent correlation between the test forages and their chemical composition. In fact Tribe (1950b) commented that "the most common mistake regarding palatability is the idea that each plant species has its own special measure of palatability" and Heady (1964), as if complementing Tribe, said, "no single plant characteristic has been found that is isomorphic with one behavioural process".

Figure 2. Distribution of forage utilization between 07-19 hrs by small ruminants in the village setting of southern Nigeria.

Literature cited

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