Chemical composition and nutritive value of some tropical by-product feedstuffs for small ruminants — in vivo and in vitro digestibility

Abstract

Chemical composition and nutritive values of by-product feedstuffs (BPF) used for small ruminants were evaluated. Four BPF from groundnut shells (GNS), maize cobs (MC), cassava peels (CaP), and citrus pulp/peels waste (CPPW) were used to prepare complete diets fed to goats and sheep in separate trials. Twelve goats and 16 sheep 16–18 months old weighing on average 12.96±0.28 and 14.05±0.18 kg, were divided into three and four groups, respectively, and used in two separate growth and digestibility studies. In vitro digestibility trial was carried out. In vivo and in vitro data were compared. Chemical composition of BPF differed in nutrient contents. MC had the least crude protein content (3.4%). CaP and CPPW had low NDF and ADF. GNS and MC were higher in cell wall constituents. Voluntary DMI was expressed as g/kg live weight (LW) per day and this ranged between 58.0–62.0 g/kg LW per day in goats and 70.0–83.0 g/kg LW per day in sheep. DM and CP digestibility were better ( P>0.05) in goats fed CaP diet compared to the other BPF. NDF digestibility was better ( P>0.05) in the GNS fed group compared to MC and CaP groups. GE was lower in CaP fed goats than in the others. Nutrient digestibility of the four by-products was better ( P>0.05) in sheep that received CPPW diet. Other by-products (GNS, MC, CaP) digestibility followed the trend observed in goats. Net gas production, DM, NDF and OM digestibility and metabolizable energy (ME, MJ/kg of DM) were significantly different among the BPF ( P<0.05). GNS had low net gas production than MC however, gas production was highest in CPPW followed by CaP. The low NDF values in CaP and CPWM indicated that they contain more soluble materials which ruminants can benefit from. In in vivo trial, goats and sheep performed better with rations formulated from CaP and CPPW compared to other BPF such as MC and GNS. However, the high gas production observed shows that care has to be exercised in feeding them to animals at high levels to avoid accumulation of gases and fermentation products which could lead to displaced abomasum and acidosis. The results indicate that estimates of digestibility are of use for BPF evaluation and these estimates can be readily accomplished by the in vitro techniques available. In conclusion, in vitro OM digestibility for GNS, MC, CaP and CPPW were higher compared to the in vivo digestibility.