Determining availability of nutrients in sweetpotato grown in the Kenyan highlands using in sacco degradability and in vitro digestability.

Abstract

Six sweetpotatoes cultivars, specifically Naspot1, 103001, Kemb23, Gweri, Kemb36 and Wagabolige, were grown in three agroecological locations within the highlands of Kenya: (i) Nyeri County (high altitude); (ii) Nandi County (medium altitude); and (iii) in Bomet County (low altitude). The principal factors related to sweetpotato's protein and energy digestibility are protein and dry matter content, trypsin inhibitor activity and starch digestibility. Considerable variation exists in intestinal digestion of protein among and within different protein sources, and this variation can possibly be influenced by the area where the forage was grown, the nutrient content and various other factors. The high degradability of sweetpotato suggests that it can be good protein forage and accumulation of this type of information will ensure that protein supplements are allocated on the basis of their flow rate from the rumen with a given type of diet. The digestibility and rumen in vivo (in sacco) degradation are some of the major tools used in assessing the value of a feed because they give an indication of the proportion of the feed that is digested and therefore, available for absorption. Samples of storage roots and vines of the six sweetpotato cultivars were oven dried, milled to pass through a 3 mm screen and pooled. A subsample of 3.0 g was taken for digestibility analysis and in vivo degradation determination. A general linear model (GLM) in a three way factorial arrangement of the statistical software sas version 9.1 was applied to compute analysis of variance (ANOVA) to test for any significant differences in in vitro digestibility. A GLM in a complete randomized design of sas version 9.1 was used to compute ANOVA to test for any significant differences on in vivo degradability. There was a significant difference in vine and storage roots' in vitro organic matter digestibility (IVOMD) due to variation in locations (P<0.05), cultivars (P<0.05) and management (P<0.05). There was also significant interaction between management and cultivars (P<0.05) both in vines and storage roots. Gweri overall had the ratoon with the highest IVOMD among all the varieties, while medium-altitude Nandi was the location with the highest average IVOMD. In vivo degradation characteristics of vines and storage roots of various sweetpotato cultivars indicated that there was a difference in solubility or washing loss (P<0.05) and degradation potential (P<0.05) of both vines and storage roots in various cultivars. The high degradability and degradation of sweetpotato suggests that it can be good protein and energy forage.