Rumen dry matter degradability and preference by West African Dwarf goats for selected multipurpose trees in Nigeria

Leaves and tender stems of eleven species of trees were sampled and analyzed for proximate and mineral compositions as well as for rumen degradability and preference by WAD goats.

Crude protein content varied from 17.5% for Dialium guineense to 29.9% for L. leucocephala. The average crude fibre content was 19.8%. There was no significant difference in nutrient composition of legume and non-legume browse types. Ca content ranged from 0.02% for Alchornea cordifolia to 1.10% for Grewia pubescens while P content ranged from 0.004% for Calliandra calothyrsus to 0.2% for A. cordifolia. Potential degradation varied from 32.8% to 87.5% for D. guineeense and A. cordifolia respectively while effective degradability was highest in G. pubescens and least in Xylia xylocarpa. G. sepium was the most preferred species by WAD goats followed by D. guineense while Milletia thonningi and Enterolobium cyclocarpum were least preferred. D. guineense, Inga edulis, A. cordifolia and G. pubescens had comparable nutritive value with L. leucocephala and G.sepium and were recommended as potential ruminant feed resources.

Introduction

The incorporation of trees into farming systems is a viable option to profitable and sustainable crop and livestock production. Trees help to reduce reliance on fertilizers, minimize soil erosion, maintain soil fertility, ensure plant diversity and provide a range of useful products like fodder, mulch, timber, food, medicine and crop protection. In Africa, a wide range of tree species are available but only few have been given detailed nutritive characterization taking into consideration both plant and animal factors. In Nigeria, the two exotic browse species, Leucaena leucocephala and Gliricidia sepium have shown appreciable forage potentials. However, their adoption by farmers is faced with limitations like pests and diseases, such as psyllid attack on Leucaena. Furthermore, most native species shed their leaves during the dry season and majority of them possess physical structures and anti-nutritive chemical compounds that are said to protect them against herbivores (Coley et al 1985), but could reduce their palatability as well as limit their nutrient availability and digestibility (Barry 1989).

There is therefore, an urgent need to identify alternative tree species as potential fodder sources which are less unencumbered by morphological, biochemical or cultural limitations in livestock nutrition. This is the basis of the present study with the objective to determine the proximate and mineral compositions, rumen dry matter degradability and preference by West African Dwarf goats of eleven multipurpose tree species with L. leucocephala and G. sepium as controls.

Materials and Methods

The study was conducted at the Teaching and Research Farm, University of Ibadan and the International Livestock Research Institute (I.L.R.I.), Ibadan in the rain forest zone of southwestern Nigeria. The species used in the study were harvested in the early dry season (November) from the arboretum of International Institute of Tropical Agriculture (I.I.T.A.), Ibadan and consisted of the followings: L. leucocephala (control), Calliandra calothyrsus, Enterolobium cyclocarpum, Inga edulis, Grewia pubescens, Pterocarpus santalinoides, G. sepium (control), Dialium guineense, Prosopis africana, Milletia thoningii, Alchornea cordifolia, Xylia xylocarpa and Albizia niopoides. Leaves were harvested from at least 10 different trees and then pooled. Samples for chemical analyses were oven dried at 60 °C for 48 h, ground to pass through a 1 mm sieve and then analyzed for proximate and mineral compositions (AOAC 1995). N content was determined using the Kjedahl method and crude protein (CP) calculated as N × 6.25. Dry matter (DM) was determined by drying fresh samples in the oven at 105ºC for 24 hours and ash by igniting the samples in a muffle furnace at 525 °C for 8 h. Nitrogen-free extract (N.F.E.) and organic matter (OM) were determined by difference. Calcium content was determined by flame photometry and Phosphorus by the phosphomolybdate method after digesting the samples.

Samples for dry matter degradability were sun-dried and ground to pass through a 2.5 mm sieve and 3g of each sample were measured in triplicates into weighed Dacron bags. These were then tied onto rubber loops and inserted into the rumen of three matured West African Dwarf (WAD) goats fitted with permanent rumen cannulae for a period of 6, 24, 48 or 72 hours of incubation. After each incubation period, the samples were thoroughly washed under tap water until the water became colorless. Washing loss, or degradability at zero hour, was determined by soaking nylon bags containing 3g of each sample in ordinary warm water (37ºC) for one hour. The bags were then dried to constant weight at 65ºC. The DM degradability of each sample at each incubation time was calculated as the difference in the quantity of DM in the bags before and after incubation (Ørskov et al 1980). The goats used for the experiment were kept in individual pens and were fed on a diet of fresh Panicum maximum (60%) and concentrate (40%). They had unrestricted access to water and mineral licks.

Relative preference for each species was determined using the cafeteria technique (Larbi et al 1993). It was conducted over a fourteen-day period divided into seven days each of adjustment and data collection respectively. WAD goats (n = 6) averagely weighing 12.7 kg were used. On each collection day, 500g fresh leaves of each species were offered in separate feeding troughs for one hour. The troughs were randomly placed around the perimeter of an 8m² floor pen. Left-over was weighed immediately after to determine consumption of each species. A daily relative preference index for each species was calculated by dividing quantity consumed of the species by the value for the species with highest consumption and multiplying the result by 100. Browse species were ranked based on mean preference index.

where P = DM degraded in rumen at time t, a = the rapidly soluble fraction, b = the insoluble but fermentable fraction, c = the constant rate of degradation of b (% h^-1), a +b = potential degradability (PD) or extent of degradation and t is the rumen incubation time (Ørskov & McDonald, 1979). Effective degradability (ED) was calculated by applying the equation

Values for a, b, c, PD, ED were subjected to analysis of variance (SAS, 1998). The statistical model adopted was

Where Y_ij= record of the i_th species measured in the j_th goat; µ = common mean; α_i= effect of the i_th species; β_j = effect of the j_th goat; e_ij=uncontrolled environmental and genetic error. Means were separated by least significant difference. Linear correlation and regression analyses were performed using a scientific calculator (Casio fx-7400G PLUS POWER GRAPHIC model) to show the relationship between nutrient composition, DM degradability and preference index values.

Results and Discussion

From Table 1, average DM content of the selected browse plants was comparable with 38.7% for selected leaves of shrubs and trees in Nigeria (Ikhimioya 2008) and 40.8% for jackfruit leave (Ly et al 2001). Species with DM contents >40% probably have hard and coarse leaf texture, as reported by Daovy et al (2008) for mango leaves. Mean CP content (22.1%) is higher than 14.7% obtained by Ngodigha and Oji (2009) for tropical browse plants. This suggests that the evaluated species have the potential to supply moderate to high levels of CP and can therefore be used as protein supplements to tropical grasses and other low quality feeds in ruminant diets. Difference in CP contents of leguminous (L) and non-leguminous (NL) browse species were not significant. This contradicts the findings of Cobbina et al (1990) and Larbi et al (1993), probably because two NL species against eleven L species were used in the study. Mean ash content compares favourably with that reported by Topps (1992) while mean Ca and P contents were slightly lower than those reported by Kabaija and Smith (1988), probably due to differences in species, climatic and edaphic factors. Apart from A. niopoides, Ca:P ratio in all the species are higher than recommended, although the mean is within the range (1:1 – 1:7) in which no harmful effect may occur to the animal, provided the level of the two minerals in the diet are adequate (Underwood 1981).

Table 1. Proximate and mineral compositions (%) of browse species
Species	DM	CP	CF	EE	Ash	NFE	Ca	P
G. sepium	31.6	24.4	14.2	3.14	9.63	48.6	0.740	0.09
D. guineense	45.0	17.2	21.5	4.02	8.80	48.6	0.340	0.1
I. edulis	43.8	17.3	22.0	3.17	8.42	49.8	0.700	0.04
L. leucocephala	34.3	29.9	17.4	2.40	9.65	40.7	0.740	0.12
G. pubescens	37.2	28.9	22.1	2.33	8.37	38.3	1.100	0.12
A. cordifolia	34.2	18.7	17.3	3.36	9.14	51.6	0.020	0.2
A. niopoides	32.3	23.3	19.4	3.23	9.25	44.8	0.220	0.12
X. xylocarpa	48.2	18.1	32.1	3.45	9.64	36.7	0.840	0.1
P. santalinoides	32.9	19.8	13.5	3.50	9.02	54.1	0.920	0.04
C. calothyrsus	40.5	27.7	10.4	3.02	9.80	49.1	0.720	0.04
P. africana	47.2	19.6	22.1	4.10	9.09	45.2	0.480	0.12
M .thonningi	30.7	21.4	31.1	2.22	8.61	36.7	0.760	0.08
E. cyclocarpum	39.3	20.4	17.6	3.42	9.47	49.1	0.520	0.12
Mean	38.3	22.1	20.1	3.18	9.15	45.6	0.620	1.01
SEM	5.95	4.25	6.04	0.56	0.47	5.55	0.290	3.17
SEM = Standard error of the mean

Table 2 shows that the species differed significantly (P<0.05) in rumen DM degradability parameters. Leucaena had the highest soluble fraction (33.98%) while D. guineense had the least (8.19%). Higher level of soluble fraction is known to result in a more efficient fermentation in the rumen (Beever et al 1978).The differences in soluble fraction could be attributed to the proportion of soluble carbohydrates to structural carbohydrates (Ngodigha and Oji 2009). According to Van Soest (1982), the soluble carbohydrates ferment faster than structural carbohydrates and their relative proportions are determined by differences in the stage of maturity. This is probably why Leucaena with moderate CF content had the highest soluble fraction and X. xylocarpa with the highest CF content had the least soluble fractions, apart from D. guineense. Degradable fractions (b) in G. pubescens and A. cordifolia were comparable and significantly higher than in other plants. Both species could therefore have better potential as sources of highly fermentable nutrients than the other plants especially since they have moderate to high crude protein contents.

Rate of degradation (c) varied from 0.3% h^-1 in A. niopoides to 3.9% h^-1 in P. santalinoides. Abdulrazak et al (1996) found that ‘c’ values of foliage from G. sepium and L. leucocephala fluctuated from 5.2 to 7.6%/h and from 4.0 to 5.2%/h, respectively, while Alayón (1996) estimated a degradation rate of 10.7%/h for G. sepium foliage. These values are higher than those obtained for both species in this study, probably due to the difference in the basal diets fed to the experimental animals, ages of the leaves used and species of fistulated animals (Ezenwa and Kithara 2001). The faster degradation of

Table 2. Dry matter degradation characteristics of browse species (%)
Species	a	b	c	a + b	ED
G. sepium	29.99^a	36.89^bc	1.42^b	66.87^bc	45.3^b
D. guineense	8.19^c	24.61^c	2.88^ab	32.80^d	22.7^d
I. edulis	17.02^b	42.85^b	1.10^bc	59.87^c	32.2^c
L. leucocephala	33.98^a	48.97^b	1.49^b	82.94^a	54.9^ab
G. pubescens	25.42^ab	61.30^a	3.46^a	86.72^a	64.3^a
A. cordifolia	26.52^ab	61.01^a	0.75^c	87.53^a	43.2^bc
A. niopoides	25.05^ab	53.49^ab	0.37^d	78.54^a	33.4^c
X. xylocarpa	11.90^c	21.34^c	0.52^c	33.23^d	16.3^d
P. santalinoides	17.14^b	24.68^c	3.93^a	41.82^d	33.5^c
C. calothyrsus	25.00^ab	51.05^ab	2.22^ab	75.88^ab	51.9^b
P. africana	31.74^a	46.44^b	0.46^cd	81.64^a	40.4^bc
M .thonningi	24.53^ab	46.07^b	0.50^cd	69.27^b	33.7^c
E. cyclocarpum	32.56^a	19.71^c	1.21^bc	52.29^c	39.9^bc
Mean	23.77	41.42	1.56	65.34	39.4
SEM	7.70	14.09	1.15	18.96	12.5
Probability	0.46	0.49	0.31	0.49	0.49
a=soluble fraction; b=slowly degradable fraction; c=rate of degradation (%/hour); a+b=potential degradability; ED=effective degradability; ^{a, b, c, d}Means within the same column with different superscripts are significantly different (P<0.05);SEM = Standard error of the mean

DM of P. santalinoides, G. pubescens, and D. guineense could be advantageous, which may probably release greater rumen metabolites, enhance rumen microbial functions and proliferations, improve the rumen ecology (i.e., N, minerals and isoacids), and they may further enhance forage intake since they move out of the rumen faster and thus reduce rumen fill (Bonsi et al 1995).

Potential degradation increased markedly from 32.8% in D. guineense to 87.53% in A. cordifolia. This compares with 30.4 % to 80.9 % reported by Bamualim et al (1980) for tropical browse legumes. According to Von Keyserlingk et al (1996), the higher the CP content of forage, the higher the effective degradability. This was confirmed in this study as G. pubescens with the highest ED had very high crude protein content while X. xylocarpa with the least ED had one of the least CP contents.

Table 3 shows the average preference index (API) values and ranking of the evaluated species. The highest preference ranking of G. sepium in this study is probably because it is the most familiar to the goats at the time of the study since according to Ikhimioya (2008), goats more readily accept feeds with which they have had previous experience. The result is in contrast with Larbi et al (1993) and Odeyinka (2000) who reported low preference for G. sepium leaves which according to Lowry (1990) are refused by animals on the basis of smell, and is often rejected without being tasted, suggesting that the problem lies with volatile compounds released from the leaf surface. These compounds probably include coumarin which imparts a repulsive odour on leaves and barks (Lana et al 1989) and other phytochemical compounds (Russel and McDonald 1992).

However, the result agrees with Mejia et al (1991) who stated that G. sepium was selected in preference to all other feeds and also with Brewbaker (1986) that it is highly acceptable to animals when fed in a cut and carry method. There is therefore an apparent variation in the acceptability of G. sepium by ruminant animals in different parts of the world. Factors responsible for this probably include climatic or edaphic effects on leaf chemical composition, differences in behaviour or in rumen flora between animals in different places (whether genetically or environmentally caused), or genetic variation in Gliricidia itself (Simons and Stewart 1994).

The 2^nd and 3^rd ranking recorded for Dialium and Inga in this study is probably a reflection of the coarse nature of the leaves judging from their very high dry matter contents since according to Quedrago et al (1996) goats prefer coarse feeds. Larbi et al (1993) equally reported a high acceptability of Dialium by small ruminants. Species like Calliandra, Milletia and Enterolobium were least preferred probably because of lack of previous experience by the goats or presence of strong smell resulting in aversion for the species by goats (Simons and Stewart 1994).

Table 3. Average preference index (API) values and ranking of MPT species
Species	API	Rank
G. sepium	0.99	1
D. guineense	0.93	2
I. edulis	0.56	3
L. leucocephala	0.53	4
A. cordifolia	0.39	5
G. pubescens	0.27	6
X. xylocarpa	0.09	7
A. niopoides	0.03	8
P. santalinoides	0.02	9
P. africana	0.01	10
C. calothyrsus	0.005	11
M .thonningi	0.004	12
E. cyclocarpum	0.004	13
Mean	0.29
S.E.M	0.34

From Table 4, correlations between API and chemical components were non-significant, in contrast to the findings of Lambert et al (1989) that preference in sheep and goats correlate positively with CP content of forages. However it is similar to the reports of Hadjigeorgiou et al (2003) and Ikhimioya (2009). Also, non-significant correlations were obtained between API and DM degradation characteristics.

Table 4. Linear correlation and regression coefficients of some proximate and degradability components (X) with API (Y)
Nutritive Parameter	Correlation	Regression Equation
DM	-0.02	Y=0.33-0.001X
CP	-0.03	Y=0.35-2.39X
CF	-0.16	Y=0.48-9.22X
EE	+0.08	Y=0.14+0.05X
Ash	-0.07	Y=0.76-0.05X
NFE	+0.19	Y=0.25-0.01X
Ca	-0.11	Y=0.37-0.13X
P	+0.07	Y=0.24+0.59X
a	-0.18	Y=0.49-0.008X
b	-0.06	Y=0.36-0.002X
c	+0.17	Y=0.21+0.05X
a + b	-0.13	Y=0.45-0.002X
ED	+0.01	Y=0.29-0.0002X

Conclusions

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Received 5 September 2011; Accepted 27 November 2011; Published 4 January 2012