| Use of Trees by Livestock : Prosopis - Acacia - Gliricidia - Anti-Nutritive Factors - Quercus - Ficus - Calliandra - Erythrina |
|Use of Trees by Livestock : Erythrina|
Brewbaker (1989) suggested that Erythrina spp. had little forage potential in the African context. There are a number of reports in the literature (e.g. Jama et al., 1989; Tarawali, 1991) which indicate that introductions of a range of species have not always met with success because of agronomic and biotic problems, such as damping off of seedlings and damage caused by stem borers. Nevertheless, E. abyssinica is used in the Wolayata region of southern Ethiopia for dry season fodder, live fences and shade for coffee (Lazier and Mengistu, 1984) and its potential as a fodder tree is thought to be worthy of further study (Larbi et al., 1993). E. variegata (syn. E. indica) is one of a total of 13 fedder shrubs and trees found to be widely used in ruminant feeding systems in Asia (Chen et al., 1992), while E. arborescens is planted by Nepalese farmers in areas of 1000-1500 m altitude (Joshi, 1992). E. fusca and E. poeppigiana are of growing importance to livestock in Central and South America (Beer, 1980; Preston and Murgeitio, 1987; Preston, 1992; Kass et al., 1992).
In the humid tropics of Costa Rica, E. poeppigiana interplanted with King grass (Pennisetum purpureum x P. typhoides hybrid) in blocks and pruned three or four times per year, gave dry matter yields of tree fadder ranging from 6.4 t/ha/year at a density of 1667 trees/ha to 11.3 t/ha/year with 3333 trees/ha (Benavides et al., 1989). When planted at high density in fertilized, pure stands, E. berteroana produced 19.4 t/ha/year of DM in three harvests (CATIE, 1989). In a similar climatic region, where several Erythrina spp., including the native species E. berteroana, E. fusca and E. globocalyx, together with E. poeppigiana of South American origin, are commonly used as living fences (Sauer, 1979), fouryear-old trees of E. berteroana, established from large stakes, yielded 319 kg DM of leaves and stems from 100 m of fence line (169 trees) after eight months growth (Budowski et al., 1985). With typical planting arrangements where trees are grown at spacings ranging from 1-3 m, annual DM yields in the range of 1.8-3.0 t/km of fenceline were obtained (CATIE, 1989).
Many Erythrina spp. are well accepted by many classes of livestock. The leaves of E. variegata are eaten by cattle in India (CSIR, 1986), while both the leaves and the young flowers of E. sigmoidea are relished by zebu cattle in Cameroon (Audru, 1980). Goats consumed leaves of E. poeppigiana at a daily level of up to 3.2 kg DM/100 kg liveweight (Samur, 1984), while sheep and goats consumed E. abyssinica at levels of 3.0 and 2.8 kg OM (organic matter)/100 kg of metabolic weight (Larbi et al., 1993). The fruit of E. edulis is consumed by pigs in Colombia (Preston and Murgeitio, 1987), while in Indonesia (Raharjo and Cheeke, 1985), rabbits ate up to 23% of their diet as chopped leaves of E. subumbrans (syn. E. Iithosperma).
The nutritive value of Erythrina spp. is generally held to be good, although published data are scarce. Representative values are presented in Table 1. Crude protein (CP) contents of 30.Ã³, 11.3 and 13.8% respectively have been reported for the leaves, stem and bark of E. poeppigiana (Preston and Murgeitio, 1987). The CP content of dried and ground leaf meal of this species, averaged over seven individual evaluations in Costa Rica, was 26.1 % (calculated from Kass et al., 1992). The CP content of leaves and stems of E. berteroana (at 8 months growth) were similar at 26.3 and 8.1 % respectively (Budowski et al., 1985).
The in vitro dry matter digestibility of the leaves and stems of E. poeppigiana appears to be somewhat variable, but moderate and in the range of 44-53% (Samur, 1984; Preston and Murgeitio, 1987; Rodriguez et al., 1987; Benavides et al., 1989; Kass et al., 1992). The variation could be due to differing analytical techniques, or to varying amounts of stem in the samples, although Salazar and Vasquez (1988) observed considerable genetic variation in morphology between different provenances of this species in Costa Rica. This variability may also be reflected in the nutritional value of the foliage. The bark had a remarkably high level of digestibility which Preston and Murgeitio (1987) reported to be 78%.
The published literature is sparse but available data suggest that some African and Asian species of Erythrina may be lower in protein content and higher in digestibility, at least in small ruminants, than the better known American species. Chopped and wilted leaves of E. abyssinica from Ethiopia had CP levels of 20.6% with in vivo DM digestibility of about 65% in both sheep and goats. This species was considered to show promise as a cheap source of protein (Larbi et al., 1993). The protein content of a single sample of E. arborescens from Nepal was only 16.9% (Josh), 1992), but this figure could be artificially low if an unusually high proportion of edible stem was included in the sample.
Dried leaves of E. variegata showed in sacco DM disappearance of only 36% after incubation in cows of 12-72 hours, but 60% of the CP was degraded (Huq and Saadullah, 1987). These results suggest that Erythrina leaves may be more effective when used to supplement poor quality pastures than would be predicted on the basis of laboratory evaluation of dry matter digestibility alone.
In Costa Rica, where it is common to supplement dairy cattle with concentrates based on soyabeans, the replacement of the concentrate with E. poeppigiana foliage resulted in a linear decrease in daily weight gains in young heifers and in the milk yields of cows. Dry matter intake of grass was also reduced. The growth rate of grazing steers on unsupplemented diets, however, increased when the steers were fed low levels of E. cocleata fodder, and growth rates were further improved by the addition of an energy source such as green bananas or molasses. Work with rice
bran suggested the need to supply bypass nutrients (both energy and protein) to obtain high milk yields when Erythrina fodder was offered to dairy cattle as the main source of dietary nitrogen. It was concluded that under lowland humid conditions, the direct benefits to milk production from the use of Erythrina forage would be small where alternative, conventional concentrates were available. There may, however, be important indirect benefits such as increased carrying capacity of pasture as a result of fodder substitution, and improved nutrient recycling within the grazing area. The financial benefits would be site-specific, depending on relative costs and returns. In subhumid regions, supplementation of poor quality roughages with tree foliage may be an attractive method of improving animal productivity and profitability (Kass et al., 1992).
The foliage of Erythrina spp. appears to be particularly attractive to small ruminants. Milk yields of dairy goats fed on a basal diet of King grass (Pennisetum purpureum) and reject bananas were increased linearly by 84-156% when the animals were given leaves of E. poeppigiana at daily levels of 0.5-1.5 kg DM/100 kg liveweight. The percentage increase was similar for goats with both high and low initial milk yields (Esnaola and Rios, 1990). Animals consumed 16% more foliage of E. poeppigiann than Gliricidin sepium when offered under similar conditions, and daily milk yields increased by some 15% (Rodriguez et al., 1987). The tree fodder produced lower increases in yields than commercial concentrates with the same level of CP, suggesting that the tree protein was of lower nutritional value than conventional supplements. Using costs and returns from Costa Rica, economic analyses strongly favoured the use of Erythrina fodder over concentrates based on soyabeans (Kass et al., 1992).
The weight gains of young, castrated male sheep and goats fed over an 80-day period on a basal diet of Napier grass (Penissetum purpureum) almost doubled when the diet was supplemented with chopped, wilted leaves of E. abyssinica at rates of up to 1 kg/head/day (Larbi et al., 1993). Again, the response to increasing levels of the tree fodder appeared to be linear.
In general, with small ruminants fed on King or Napier grass, there was a partial substitution of Erythrina for the basal diet, but total dry matter intake increased as a result of the feeding of the tree fodder (Kass et al., 1992).
The high nutritional value of the genus in terms of digestible crude protein is sufficient to justify its use as a protein supplement to improve the feeding value of diets based on poor-quality grass or roughage.