Leguminous tree foliage is potential source of protein and minerals and could be employed as supplements to non-legumes to increase the level of production of livestock. The protein content in fodder legumes consist of both soluble and insoluble compounds and as such is used both as an important source of nitrogen for increased rumen microbial activity and by-pass protein for supplying amino acids to the lower gut of the host animal (Leng, 1997). In addition, fodder legumes are also important source of minerals but poor source of manganese, zinc and phosphorus. Supplementation of fodder legumes in the feed of ruminant animals up to about 35% does not seem to have any effect on the intake of fibrous feed materials. As such the intake of DM is often increased by the amount of green fodder given to the animal. However, the presence of tannins in both legumes and non-legumes limits utilization of both species as they can reduce the feed intake, nutrient digestibility and protein availability (Silanikove et al. 2001). Nevertheless, some tanniniferous feeds have beneficial effects in ruminant diets by improving nitrogen utilization efficiency and amino acid absorption. Condensed tannins also have biological effects on the control of gastro-intestinal parasites; possible direct effects could be mediated through CT-nematode interactions, which reduce nematode viability (Nguyen et al. 2005). A management strategy to reduce negative effects of tannins in fodder trees could be to feed mixtures of low and high tannin content species, which could create positive effects on in vitro GP, rumen degradation and digestibility of diets (Castro-Gonzáles and Alayon-Gamboa, 2008). A better understanding of the effects of low and high tannin foliage mixtures on nutrient digestibility and methane mitigation properties would improve management of such resources (Naseri et al. 2017). This knowledge would be of considerable importance to Nigeria for the efficient utilization of tree forage, and research must be established to develop feeding strategies to overcome undesirable effects when using tanniniferous foliage. This study evaluated the nutritive value legume with low tannin on in vitro GP and fermentation characteristics.
MATERIALS AND METHODS
Experimental location and forage samples
All the forages were harvested from Gwoza Local Government Area, Borno State, Nigeria. The area is located at 11.05˚ North and 30.05˚ East and at an elevation of about 364 m above sea level in the north eastern part of Nigeria. The ambient temperature ranges between 30 ˚C and 42 ˚C being the hottest period (March to June) while it is cold between November and February with temperatures ranging from 19-25 ˚C (Ijere and Daura, 2000). Twelve indigenous browse plants (leaves) commonly consumed by ruminant animals were sampled and used in this study. The species were: Acacia nilotica, Acacia senegalensis, Acacia seyal, Bauhenia nufescens. Daniellia oliveri, Desmodium relutinum, Dicrostachys cinerea, Erythrina senegalensis, Fadhebia albida, Parkia biglobosa, Pterocarpus erinaceus and Tamarindus indica. The browses were harvested from at least 10 trees per species selected at random in four locations within the study area at the end of the rainy season. The harvested samples were pooled for each individual tree species and oven dried at 105 ˚C for 24 h to a constant weight and ground to pass through a 1.0 mm sieve. The dried samples were sub-sampled to obtain three samples for each tree species and analysed for their composition.
In vitro gas production study
Rumen fluid was obtained from 3 West African dwarf female goats through suction tube before morning feed. The goats were fed with concentrate feed(40% corn, 10% wheat offal, 10% palm kernel cake, 20% groundnut cake, 5% soybean meal, 10% dried brewers grain, 1% common salt, 3.75% oyster shell and 0.25% fish meal and and 40% Guinea grass; Panicum maximum). Incubation was as reported by some studies using 120 mL calibrated syringes in three batch incubation at 39 ˚C. Into 200 mg sample (n=12) in the syringe was introduced 30 mL inoculums containing cheese cloth strained rumen liquor and buffer (NaHCO3+3Na2HPO4+KCl+NaCl+MgSO4.7H2O+CaCl2.2H2) (1:4, v/v) under continuous flushing with CO2. The gas production was measured at 3, 6, 12, 24, 48, 72 and 96 h. The net gas volumes data was then fitted in the equation (Menke and Steingass, 1988):
Y= a + b(1-e-c t)
Y: volume of gas produced (mL) at time t.
a: gas production from the immediately soluble fraction (mL).
b: gas production from the insoluble but degradable fraction (mL).
a + b: potential gas production (mL).
c: constant of gas production (fraction/h).
t: gas production intervals i.e. 3, 6, 12, 24, 36, 48, 72, 84 and 96 hours.
Organic matter digestibility (OMD) was estimated as OMD= 14.88 + 0.889 GV + 0.45 CP + 0.651 XA (Menke and Steingass, 1988).
Browse species were analysed for dry matter (DM), crude protein (CP), ether extract (EE), crude fibre (CF) and ash according to AOAC (2005). Crude protein was calculated as N × 6.25. The leaves samples were analysed for neutral detergent fibre (NDF), acid detergent fibre (ADF), acid detergent lignin (ADL) and cellulose according to Van Soest et al. (1991). Total condensed tannins (CTs) analysis were according to Polshettiwar et al. (2007).
Data obtained were subjected to analysis of variance in a completely randomized design using SAS (1996). Where significant differences occurred, the means were separated using the Duncan multiple range test of the same statistical package.
RESULTS AND DISCUSSION
The chemical composition of the browse forage leaves is presented in Table 1. The examined plant leaves had high CP values ranging from 111.60 in Acacia senegalensis to 172.4 g kg-1 DM in Pterocarpus erinaceus.The highest NDF content of 532.8 g kg-1 DM was recorded in Erythrina senegalensis while Acacia nilotica had the lowest value of 336.40 g kg-1 DM. The ADF level in the experimental leaves ranged from 231.4 g kg-1 DM in Bauhenia nufescens to 431.6 g kg-1 DM in Erythrina senegalensis. Acacia seyal had the least lignin content of 92.0 g kg-1 DM while Parkia biglobosa had the highest value of 131.60 g kg-1 DM. Total condensed tannins varied from 0.09 mg/g DM in Acacia senegalensis to 0.62 mg/g DM in Erythrina senegalensis. A range of 0.32 mg/g DM in Fadhebia albida to 0.46 mg/g in Bauhenia nufescens was obtained for phenolics. The in vitro organic matter degradability (IVOMD) was generally low, except for Acacia seyal (71.25%) and Fadhebia albida (74.29%) which had high values. The family and local names of the browse forage samples studied is presented in Table 2.
In vitro gas production
The in vitro cumulative GP of the browse fodders is presented in Table 2. The forages significantly (P<0.05) differed in the GP; Pterocarpus erinaceus had the highest GP (29.33 mL/200 mg DM) throughout the incubation periods from 3 to 96 h while Parkia biglobosa produced the least gas volume of 2.00 ml/200 mg DM at 48, 72 and 96 h of incubation.
Fermentation characteristics of semi-arid browse forages
The GP from the immediately soluble fraction (a) as shown in Table 3 is generally low for all the browse forages, with values ranging from 2.67 in Acacia senegalensis to 6.00 mg/200 g DMinErythrina senegalensis and Pterocarpus erinaceus. The value for GP for insoluble but degradable fraction (b) was highest in Dicrostachys cinerea (17.00 mL) and least in Acacia seyal and Fadhebia albida (7.00 mL). The potential gas production (a+b) was generally low for all the browse forages with the highest value (21.00 mL) in Dicrostachys cinerea and the least value (10.00 mL) in Fadhebia albida. The rate of GP (c) ranged from 0.97 in Acacia senegalensis to 0.46 in Desmodium relutinum. The GP production (Y) at time‘t’ ranged between 6.00 in Fadhebia albida and 13.67 mL/200 mg DM in Erythrina senegalensis and Pterocarpus erinaceus.
Correlation coefficient (r) between chemical composition and in vitro