MATERIALS AND METHODS

Experimental site: The study was conducted at the Teaching and Research Farm of the Ladoke Akintola University of Technology, Ogbomoso, Oyo State, in the south western part of Nigeria. Ogbomoso is in the derived Savanna zone and situated at about 600 m above sea level and located on latitudes 8° 07' N and 8° 12' N and longitudes 4° 04' and 4° 15' E (Oguntoyinbo, 1978). Ogbomoso has a maximum temperature of 33°C and a minimum temperature of 28°C. The humidity of the area is high (74%) all year round except in January when the dry wind blows from the north and the annual rainfall is over 1000 mm (Olaniyi, 2006).

Forage materials: MO, LEU and GLI leaves were harvested from existing plantations at the Teaching and Research Farm after a cut-back period of 60 days in March 2010; the peak of the dry season. The leaves of each of the three browses were pooled together separately and air-dried to constant moisture levels and thereafter bagged separately for later use.

Animals, experimental design and management: Three male West Africa Dwarf (WAD) goats, weighing 10±1 kg, were used for this study in a 3*3 Latin Square within a complete randomized design with three treatments and three experimental periods of 24 days each. Two consecutive periods were separated by 7 days animal rest. During the rest periods, the goats were fed freshly-harvested Panicum maximum, Gliricidia sepium and dried cassava peels. The animals were purchased from a local small ruminant market in Ogbomoso. These animals were quarantined for three weeks prior to the commencement of the study. During this period, they were treated with oxytetracycline antibiotic injection for three days, drenched with Amprolium against coccidia, administered Ivermectin against ecto-parasites and gastrointestinal nematodes and vaccinated against pestes des petit ruminant (PPR). During this period, the animals were fed freshly-harvested Panicum maximum, Gliricidia sepium and dried cassava peels. The animals were thereafter housed in individual metabolic cages designed for the complete separation of faeces and urine and were adapted for an initial period of 7 days. The adaptation period was followed by 10 days of feed intake measurements and 7 days of faecal and urine collection phase consecutively. The animals were provided with access to mineral-salt lick and fresh clean water through the duration of the experiment.

There were three dietary treatments, namely:

During the feed intake measurement phase, feed refusals were collected each day and weighed to assess intake before any new feed was offered. The animals were fed at 4% of body weight (dry matter basis) while the animals were restricted to 90% of their average dry matter intake during the faecal collection phase to minimize/eliminate feed refusal. Previously air-dried leaves were used in preparing the experimental diets and foliage combinations were thoroughly mixed manually to minimize/eliminate animal preference/selection.

During the urine and faecal collection phase, urine and faeces voided by each animal were collected and measured between 08.00 and 09.00 h before morning feeding. A dustpan and brush were used to collect faeces each morning before feeding. Total daily faecal output for each goat was weighed before 10% of daily faecal output by each animal was taken for dry matter determination. Faeces were bulked separately for each goat during each period; milled with a simple laboratory mill and stored in airtight bottles until required for further analysis. The urine from each animal was collected in 5 mL of 5% H₂SO and measured. Ten percent aliquot solution was taken daily frozen until needed for nitrogen analysis. One hundred gram samples of experimental forages were taken daily during the collection period and analyzed for dry matter by drying at 70°C for 24 h and stored at ambient temperature for later analysis for proximate constituents. Samples of daily feed refusals were also analyzed for their proximate contents.

Chemical analysis: At the end of the experiment, stored forages, refusals and faecal samples were pooled together and separately re-dried to constant weight, ground using a simple laboratory mill and subsequently analyzed for the proximate contents using the standard methods of AOAC (2000) The ADF and NDF fibre contents of the experimental forages were determined by the methods of Van Soest et al. (1991). The urine samples for each animal were pooled together, defrosted and analyzed for nitrogen contents also the standard method of AOAC (2000). For mineral analysis, samples were dry-ashed at 600°C for 4 h, followed by wet digestion of the resulting ash. Ca, Na, Mg, P, Mn, Zn, Cu and Fe levels were measured with an atomic absorption spectrophotometer while K was determined using a flame photometer. The nutrient and mineral compositions of the mixed fodder diets were computed from the values obtained for the single fodders.

Statistical analysis: The data on the animal performance indices were subjected to analysis of variance using the General Linear Model of SAS (1998). Significant differences between means were separated using the Duncan’s New Multiple Range Test (DNMRT) of the same package.

RESULTS

Nutrient and mineral compositions of the experimental fodders/fodder combinations: The nutrient compositions of the experimental fodders, singly and in the investigated combinations, are as shown in Table 1. Crude protein concentrations of the fodders ranged from 21.64 g/100 g for the sole Gliricidia fodder to 28.86 g/100 g for the sole Leucaena fodder. As for the fibre components, the NDF varied between 26.35 g/100 g for the sole Moringa fodder to 29.60 g/100 g for the sole Gliricidia fodder while the ADF was in the range of 40.40 g/100 g for the sole moringa fodder to 42.80 g/100 g for the sole leucaena fodder. All the fodders, singly and in combinations, were high in organic matter with values around 90 g/100 g. The macro-mineral levels of the experimental fodders/fodder combinations were compared to the critical levels recommended by McDowell (1985) to cover the requirements of ruminants as well as diet requirements by goats (Table 1). All the macro-mineral levels, except P in the sole Leucaena and sole Gliricidia fodders which was at the borderline (0.24; 0.25 g/100 g DM), were higher than the recommended critical levels. Among the sole fodders, only Moringa contained Na at a level (0.20 g/100 g DM) higher than the 0.07 g/100 g DM required in the diet of goats. However, it was observed that combinations of Moringa fodder with either of the two other fodders corrected for the observed shortfalls in macro-mineral levels.

Table 1:	Nutrient and mineral compositions of experimental fodders/fodder combinations fed to West African Dwarf goats
MO: Moringa oleifera, LEU: Leucaena l eucocephala, GLI: Gliricidia sepium, DM: Dry matter, CP: Crude protein, EE: Ether extract, CF: Crude fibre, NDF: Neutral detergent fibre, ADF: Acid detergent fibre, OM: Organic matter, NFE: Nitrogen free extract, Ca: Calcium, P: Phosphorus, Na: Sodium, K: Potassium, Mg: Magnesium, Fe: Iron, Mn: Manganese, Cu: Copper, Zn : Zinc, *Nutrient and mineral concentrations of mixed fodders were calculated, **Critical macro-mineral levels for goats (McDowell, 1985)

Among the micro-minerals, Fe was found in the highest concentrations (200-281 mg kg^-1) followed by Mn, Zn and Cu with values ranging from 51.50-80.00, 18.00-29.00 and 5.50-7.00 mg kg^-1, respectively. The highest concentrations of these micro-minerals were found in the sole moringa fodder. Cu and Zn were found in the least concentrations in the sole Gliricidia fodder while Fe and Mn were found in the least concentrations in the sole Leucaena fodder.

Intake, digestibility and relative feed value of experimental fodders/fodder combinations: There was no (p>0.05) diet effect on dry matter intake which ranged from 278.00 g/animal/day (49.47 g kg^-1 0.75) for animals on 50 MO:50 GLI to 288.50 g/animal/day (51.33 g kg^-1 0.75) for the animals on the sole moringa diet (Table 2). Furthermore, the apparent nutrient (DM, CP and OM) digestibility values were not (p>0.05) significantly different. Apparently higher values were however obtained in favour of the sole moringa fodder. The Relative Feed Value (RFV) was high for all the experimental diets and ranged from 188.73 for 50 MO:50 GLI to an unusually high 202.42 for the sole moringa fodder, going by the quality standards assigned by the Hay Marketing Task Force of American Forage and Grassland Council (Rohweder et al., 1978) for legume, grass and grass/legume mixtures.

Nitrogen utilization by WAD goats fed the experimental fodders/fodder combinations: Nitrogen utilization data by West African Dwarf goats fed a sole diet of Moringa oleifera foliage and in equal combinations with Leucaena leucocephala and Gliricidia sepium are as shown in Table 3.

Table 2:	Mean dry matter intake (g/animal/day), apparent digestibility (%) and relative feed value of a sole diet of Moringa oleifera and in equal combinations with Leucaena leucocephala and Gliricidia sepium leaves by West African Dwarf goats
Means in the same row with the same superscript are not statistically different (p<0.05), MO: Moringa oleifera, LEU: Leucaena leucocephala, GLI: Gliricidia sepium, DMI dry matter intake, DM: Dry matter, CP: Crude protein, OM: Organic matter, SEM: Standard error of the mean

Table 3:	Mean nitrogen utilization by WAD goats fed a sole diet of Moringa oleifera and in equal combinations with Leucaena leucocephala and Gliricidia sepium
Means in the same row with the same superscript are not statistically different (p<0.05), MO: Moringa oleifera, LEU: Leucaena leucocephala, GLI: Gliricidia sepium, SEM: Standard error of the mean

There were no (p>0.05) differences in nitrogen intake on the sole Moringa diet and 50 MO:50 LEU but both were significantly (p<0.05) higher than the nitrogen intake on 50 MO:50 GLI. Non-significant (p>0.05) diet effects were also observed for faecal nitrogen losses. Significant (p<0.05) diet effects were however observed with urinary nitrogen losses with the highest value being obtained on the 50 MO:50 LEU diet and the least losses with the sole Moringa diet. Significant (p<0.05) diet effects were however observed with urinary nitrogen losses with the highest value being obtained on the 50 MO:50 LEU diet and the least losses with the sole Moringa diet. The same pattern was observed for the total nitrogen losses in absolute terms. Nitrogen retention was positive and high for all the three experimental diets. The highest nitrogen retention values, in absolute terms and as percentages of total nitrogen intake (6.02 g g^-1; 80.37%), were obtained with the sole Moringa diet.

DISCUSSION

The observed nutrient compositions for the experimental fodders fell within earlier reported ranges (Tian et al., 1998; Odeyinka et al., 2003; Asaolu and Odeyinka, 2006; Asaolu et al., 2010). The crude protein concentrations were high compared to the mean value of tropical grass species which seldom exceed a level of 15.00 g/100 g (Reynolds et al., 1992). They were also higher than the recommended range of 7.0-8.0 g/100 g DM for efficient functioning of rumen microorganisms (Van Soest, 1994). The CP concentrations also exceeded the range of 11.0-13.0 g/100 g DM known to be capable of supplying adequate protein for maintenance and moderate growth in goats (NRC, 1981; Poppi and McLennan, 1995). The ADF and NDF values of all the experimental fodders/fodder combinations were low to moderate when compared with low quality forages which ruminants effectively degrade (Arigbede and Tarawali, 1997; Okoli et al., 2003). They also compare favourably with those reported (Oduguwa et al., 1999; Oji and Isilebo, 2000; Okoli et al., 2003) for selected browses of southern Nigeria. The organic matter concentrations for leucaena and gliricidia were comparable to those reported by Aregheore (2004) while the value obtained for Moringa was also comparable to that obtained by Asaolu et al. (2009b).

Generally, mineral elements are acknowledged to be important to proper nutrition. Many minerals, particularly Ca, P and Na, are essential for small ruminants for optimum productivity (Ghazanfar et al., 2011). Mineral contents in feed resources, their strengths and weaknesses are important to know, especially for goats where browse, forbs and weeds which have not been studied analytically very much, play such a vital feeding role (Devendra, 1995). Norton (1994) reported that Ca is rarely limiting in forage diets although legumes and browses have been indicated to have more concentration of Ca than the grasses. Minson (1990) stated that it is unlikely for Mg to be critically low in tropical forages. Unlike the macro-minerals, the requirements of goats for most micro-minerals have not been well established. However, Zn requirement for goats is put at a minimum of 10 mg kg^-1 diet dry matter (NRC, 1981) while Mn requirements may be around 20 mg kg^-1 diet dry matter (Anke et al., 1973; Gibbons et al., 1976; NRC, 1981). All the fodders, singly and in combinations were observed to contain higher levels than these estimated minimum requirements (Table 1). Copper requirements need to consider present molybdenum levels and other interfering substances such as S, Zn, Fe and Ca, although goats have not been studied sufficiently enough for any estimates (Haenlein, 1987). An Fe requirement of 100 mg kg^-1 DM intake has been stated for dairy cattle (NRC, 1978). Sheep of all classes are supposedly adequately provided with 30 mg kg^-1 DM intake (NRC, 1985). However, it had been previously reported (Lintzel and Radeff, 1931) that iron requirements of newborn goat kids may be more critical than in cattle or sheep. In addition, internal parasite infestations are usually more serious in goats than in cattle and may require higher levels to prevent anaemia, more often observed in goats than in cattle (Haenlein, 1987). The amounts of Fe present in the experimental fodders could probably be sufficient to meet the needs of a growing goat. Haenlein (1987) reported that no immediate dangers of clinical deficiency diseases due to these micro-mineral content of forages is affected by soil mineral level, soil pH, environmental temperature and season of the year.

Feed intake has been described (Masafu, 2006) a measure of diet appreciation, selection and consumption by an animal. It is a key process which determines the quantity of feedstuff which is ingested over a period of time, usually per day (McDonald et al., 1993). It is regarded as one of the major factors which determine potential animal performance other than feed digestibility (Beever, 1993). These obtained dry matter intake and digestibility results suggest equal potentials of acceptability, consumption and utilization of the experimental diets by WAD goats. Apparently higher values were however obtained in favour of the sole Moringa fodder. The observed non-significant (p>0.05) differences could be explained by the reports that voluntary dry matter intake and dry matter digestibility are dependent on the cell wall constituents (fibre), especially neutral detergent fibre and lignin (Bakshi and Wadhwa, 2004). Feedstuffs with low NDF (20-35%) are more digestible than those with more than 35% (Norton, 1994). The NDF values in this study ranged from 26.35% for the sole Moringa fodder to 27.98% for the 50 MO:50 GLI (Table 1). Relative Feed Value (RFV) is a widely accepted forage quality index in the marketing of hays in the United States of America. It was developed by the Hay Marketing Task Force of American Forage and Grassland Council (Rohweder et al., 1978). RFV combines the estimates for forage digestibility and intake into a single number. All the three experimental diets (Table 2) have potentials for energy intake as they were all higher than the baseline figure of 100. Forages are ranked relative to the digestible dry matter intake of alfalfa, assuming 41% ADF and 53% NDF with RFV of 100. The author recommended that a lower RFV forage should be included with unusually high RFV hay to slow the rate of passage. The RFV reported by Kiraz (2011) for some legume hays harvested at flowering stage were high and ranged from 138.81 and 155.07 but were lower than the values obtained in this study. Variations in the RFV of forages are associated with NDF and NDF contents, extent of forage lignifications and leaf:stem ratios (Hides et al., 1983; Wilson et al., 1991; Canbolat et al., 2006).

The nitrogen intake values obtained in this study were higher than those (3.04-3.19 g/animal/day) reported by Ajayi et al. (2005) for WAD goats fed some other forages as supplements to a basal diet of P. maximum. They were however comparable to the values reported by Asaolu et al. (2010) for WAD goats on Moringa and bamboo-supplemented groundnut hay diets. Alli-Balogun et al. (2003) reported slightly higher average nitrogen intake level of 9.2 g day^-1 for Yankassa/WAD sheep crosses fed grass supplemented with cassava foliage or groundnut hay. Fadiyimu et al. (2010) also obtained an average of 9.28 g day^-1 for WAD sheep fed various levels of Moringa oleifera as supplement to Panicum maximum. Such differences may be attributed to dry matter intake levels and nitrogen concentrations of the experimental feedstuffs. The observed non-significant (p>0.05) differences in faecal nitrogen losses agree with the findings of Black et al. (1978), Fadiyimu et al. (2010) and Asaolu et al. (2010) that faecal nitrogen was not affected by nitrogen intake. The observed trend in faecal nitrogen losses could be attributed to apparent protein digestibility which ranged from 83.88% for 50 MO:50 GLI to 89.35% and with no (p>0.05) significant differences (Table 2). As observed in this study, several earlier researchers Ajayi et al. (2005), Ahamafule et al. (2006), Fadiyimu et al. (2010), Asaolu et al. (2010) have also reported significant (p<0.05) diet effects on urinary nitrogen. The high nitrogen retention values obtained in this study (Table 3) probably indicate that the protein requirements for maintenance were adequately met by the diets (Fadiyimu et al., 2010). Ajayi et al. (2005) opined that high nitrogen retention could be as a result of high crude protein content which ranged from around 24 to almost 28% (Table 1) for the experimental diets. The nitrogen retention values suggest that the sole Moringa diet had the highest efficiency of protein utilization. Moringa oleifera had been reported in an earlier study (Asaolu et al., 2010) to improve the efficiency of protein utilization on a groundnut hay based diet.

CONCLUSION

Moringa oleifera, Leucaena leucocephala and Gliricidia sepium sufficient amounts of crude protein required by small ruminants. However, only Moringa contained sufficient amounts of P and Na that are required in the diet of goats. The intake, nutrient digestibility, nitrogen utilization and predicted relative feed values were high and comparable. Combinations of Moringa with either Leucaena or Gliricidia are recommended to allow for an optimal utilization of the available Moringa fodder its currently limited availability in Nigeria.

ACKNOWLEDGMENTS

The assistance of the support staff at the University Teaching and Research Farm is appreciated. The contributions of Mrs. Folaranmi and her team members in the laboratory are also appreciated.