Evaluation Of Forage Sweet Potato Cultivars As Feed For Ruminants

ABSTRACT

There is potential in Kenya to utilize forage sweet potato (Ipomoea batatas (L) Lam) cultivars as livestock feed. There are many cultivars of forage sweet potato in Kenya whose feeding values have not been evaluated. The objectives of the current study were: 1) evaluate forage sweet potato cultivars for crude protein (CP) yield and digestibility at different harvesting ages, 2) evaluate their conservation potential as silage or hay and 3) determine sheep growth performance and goat milk yield when fed on these cultivars. Cultivars K158, Marooko and Wagabolige recorded high CP yield (1597-1679 kg/ha) and digestibility (711-851 g/kg DM) at the four harvesting ages and their optimum content of dry matter (DM) (166-168), organic matter (OM) (880-882) and CP (170-171 g/kg DM) was at 120 days. Using weighted scoring method K158, Marooko and Wagabolige (scoring 21-24) were ranked the three most superior forage cultivars and were recommended for further evaluation. Calcium (Ca) (4.40-8.41), magnesium (Mg) (3.20-5.15), phosphorus (P) (31.01-37.38), potassium (K) (11.80-25.01), sodium (Na) (4.31-8.75 g/kg DM); cobalt (Co) (247.2-252.6), copper (Cu) (22.7-56.6), iron (Fe) (278.0-326.3), manganese (Mn) (116.2-217.4) and zinc (Zn) (136.4-180.8 mg/kg DM) in all the cultivars decreased with age. For the conservation using silage, the 5% molasses rate provided adequate water soluble carbohydrates for optimal silage fermentation (pH 4.0). Marooko (NH3-H, 5.5) fermented the best quality silage followed by K158 (6.4) then Wagabolige (6.6 % of total N). Shredding increased DM (298.8-306.2) in all the cultivars and Wagabolige dried more rapidly (330.2) than K158 (310.0) and Marooko (263 g/kg DM) when dried whole or shredded. These cultivars differed in CP (156.8-170.4), neutral detergen fibre (NDF) (373.0-397.1), acid detergen fibre (ADF) (280.3- 283.4), acid detergen lignin (ADL) (85.0-117.1 g/kg DM) and there were minimal losses due to spoilage and crop respiration during hay making. These cultivars had similar DM (93.8-98.1), OM (82.0-85.6) and NDF (37.6-38.8 g/kg W0.75) intake, DM (740.3-744.1) and OM (747.0-751.7 g/kg DM) digestibility and rumen fermentation characteristics (pH 6.80-6.86). The cultivars differed in CP (10.7-16.9 g/kg W0.75) and metabolizable energy (ME) (0.94-0.99 MJ/kg W0.75) intake, CP digestibility (737.4-821.1 g/kg DM) and nitrogen balance in sheep (2.7-4.5 g/day). Cultivars K158, Marooko and Wagabolige provided high ME (9.7-10.2 MJ/kg DM), recorded superior intake of digestible OM (74.5-75.8), CP (13.8-16.1) and NDF (27.4-30.8 g/kg W0.75).