Intake and digestibility of Acacia glomerosa and Leucaena leucocephala mixed with ammoniated rice straw in rations for growing goats

Intake and digestibility of Acacia glomerosa (A) and Leucaena leucocephala (L), mixed with ammoniated rice straw (ARS) and maize by-product fl our (CB) was evaluated for growing goats. Eight goats were used (21 kg average liveweight). A factorial arrangement 2×2, in Latin square design was conducted. The factors were 2 vegetal species and 2 inclusion levels. The study was conducted in 56 days. The cell wall intake (NDF) was superior for A vs L (652.13 vs 535.3 g/goat/day). Digestibility of organic matter (OM) was superior for A vs L (79.83 vs 71.37%). The same occurred with: NDF (83.19 vs 76.85%) and acid detergent fi bre (ADF) (81.82 vs 67.39%). Higher intake of dry matter (DM) occurred at the smallest inclusion level (18.75%). Further, the low inclusion level showed higher digestibility of DM, OM, NDF and ADF than the high inclusion level.


INTRODUCTION
There are native forages from semiarid areas in Lara State (Venezuela), that have not been evaluated as feed source for ruminants, so there is a need to evaluate species like Acacia glomerosa (A) and Leucaena leucocephala (L) as protein sources in order to try to improve animal nutrition and to promote use of local feed resources.Therefore, the main objective of this study was to evaluate intake and digestibility of rations that included A and L mixed with ammoniated rice straw (ARS) and maize by-product fl our (CB) in goats.

MATERIAL AND METHODS
An experimental Latin square design in a factorial arrangement 2 × 2 was used.The factors were: L and A foliages and level of inclusion (18.75 and 37.50%).The effect on intake and digestibility of the dry matter (DM), organic matter (OM), crude protein (CP), neutral detergent fi bre (NDF), and acid detergent fi bre (ADF) was studied.The goats were placed in individual metabolic cages during 4 experimental periods of 14 days each, each period divided into 7 days for adaptation and 7 days for measurement of consumption.Total data collection lasted for 56 days.At the end of each experimental period the treatments were rotated between animals and after 28 days 4 different animals were used.Eight Creole, male growing goats were selected from the same origin and with a 21 kg average weight.Before initiating the trial, the animals were treated to eliminate parasites and supplied with a vitamin supplement.The animals received the rations in individual cages and they received water ad libitum.The rations were offered in fi xed schedule (13.00 to 14.00 h), and the quantity of the ration corresponded to 4% of their liveweight (LW), that subsequently was increased to reach 6% of LW.The rations had the following composition: T 1 : 18.75% leaf fl our L (HHL) + 56.25% ARS + 25% CB; T 2 : 37.5% HHL + 37.5% ARS + 25% CB ; T 3 : 18,75% leaf fl our A (HHA) + 56,25% ARS + 25% CB; T 4 : 37.5% HHA + 37.5% ARS + 25% CB.Acacia glomerosa (A) and Leucaena leucocephala (L) were used as protein sources and agro industrial by-products like CB and ARS were used as source of energy and fi bre, respectively.Voluntary intake of the ration was determined by the difference among offered and rejected amounts (Moore and Waller, 1975).The apparent digestibility of DM, OM, CP, NDF and ADF (ADDM, ADOM, ADCP, DNDF and DADF, respectively) were calculated, according to AOAC (1984) by total collection method (CTH) proposed by Moore and Waller (1975).The samples were placed in a stove at 60°C during 48 h, and then grinded in a Willey mill to analyse them according to the parameters of the proximal analysis Van Soest and colorimetric (Van Soest, 1963;AOAC, 1984;Bilbao et al., 1999).The data was analysed using the Statistix (1996), for analysis of the variance and for separation of averages Tukey's test was used.

RESULTS AND DISCUSSION
The chemical composition of the feeds and rations are shown in Table 1.The content of CP and ash are similar for A and L, while A possesses higher values of NDF and ADF than L. In Table 2 it is clearly appreciated that A is superior to L in consumption and digestibility of evaluated fractions.It indicates a very interesting potential for the native species A as source of CP for goats.A clear tendency of greater digestibility of CP and fractions of the fi bre is observed for the smaller level of inclusion, this could have been caused by the content of tannins of the evaluated species.A.glomerosa presents higher values of digestibility and similar consumption values to those reported by Hove et al. (2001) for the Acacia angutissima (21.87%CP, 52.5% NDF and 38.6% ADF).He reported apparent digestibilities to be 53.76% of DM and 52.35% of OM when A. angutissima was used like complement in rations at 12.5%, with native grass hay, for goats weighing 30±1.8 kg.Somewhat similar to Acacia brevispica (21.87%CP, 42.8% NDF and 26.2% ADF) when it was offered to goats (LW = 21.5±1.2kg), as a complement in rations with Eragrostis abyssinica, reaching consumption from 631 to 660 g/goat/day when included as 39.8 and 41.2% of the ration, respectively.On the other hand the degradability of the cell wall of the ration is considerably higher than that reported for Acacia belandieri, A. farnesiana, A. greggii and A. rigidula (10.8; 39.7; 34.5 and 13.4% of DNDF, respectively) (Ramírez et al., 2000).That experiment was conducted on Pelibuey sheep cannulated in the rumen.It is understood that native goats used in this experiment could be more adapted to consumtion of plants with tannins that the Pelibuey sheep.

CONCLUSIONS
The present study indicates that A compared with L is a species with a great potential for inclusion in the diet of goats as a supplement in low protein rations, when inclusion is in the range of 18.75 to 38.5%.It should be studied deeper in relation to growth and production of goats.Also secondary compounds (like tannins) that can reduce digestibility should be studied further A. glomerosa can be promoted as a forage species in tropical dry zones.

Table 1 .
Chemical composition of feeds and rations same row indicate that means are signifi cantly different by the least signifi cant difference level (P<0.05)