Nutritive value of sweet potato (Ipomea batatas (L) Lam) forage as goat feed: voluntary intake, growth and digestibility of mixed rations of sweet potato and batiki grass (Ischaemum aristatum var. indicum)

Eight (8) growing female Anglo-Nubian × Fiji local goats, 8–9-month-old, with a pre-trial mean live weight of 12.3±0.18 kg were allotted randomly in a double 4×4 Latin Square design after having balanced the groups for age and weight. They were used to investigate the nutritive value of sweet potato forage and its mixtures with batiki grass as goat feed in terms of voluntary feed intake, growth and digestibility. The four treatments used and offered to the goats were in the following ratios (sweet potato (%):batiki grass (%)): T1, 0:100; T2, 50:50; T3, 75:25, and T4, 100:0. The aerial parts of the sweet potato forage had low DM content. CP content was influenced by morphological parts of sweet potato. Neutral detergent fibre (NDF) and acid detergent fibre (ADF) were higher in the stem and petiole than in the leaf portion. Among the morphological parts, the leaf had the lowest ADF and acid detergent lignin (ADL) contents. DM contents of the diets were between 37.3 and 40.5%. Batiki grass had a DM content slightly above that of sweet potato forage and the other experimental diets. Batiki grass had a low CP content (6.8%). Other diets had CP contents that ranged between 12.6 and 18.3%. All the diets had adequate concentrations of fibre (NDF, ADF, ADL, hemicellulose and cellulose), organic matter and metabolizable energy. There was no significant difference (P>0.05) between the consumption of batiki grass and sweet potato forage diets by the goats. The intakes of the mixed diets were significantly different from each other (P<0.05). The two mixed diets gave significantly (P<0.05) higher consumption than either batiki grass or sweet potato diets alone. Daily live weight gains of the goats were significantly affected (P<0.05) by forage type and ratios offered for consumption. The goats on the mixed diets gave better (P<0.05) live weight gains. The goats on sweet potato forage and mixed diets had significantly better-feed efficiencies (feed per gain) (P<0.05) than those on the batiki grass diet. Apparent nutrients digestibility (DM, CP, NDF, ADF, OM and energy) in the experimental diets by the goats were significantly different (P<0.05) from each other. The goats that received batiki grass gave the lowest digestibility of nutrients. In conclusion, this trial has demonstrated that sweet potato forage can support growth in goats and in combination with low quality grass such as batiki. Based on the data obtained sweet potato forage appears to be a cheap nitrogen source in the diets of growing goats.