Utilising sweet potato as a livestock feed supplement: In vitro digestibility

Recent attention on the need to improve sustainability in food production has led to a strong focus on reducing food waste, including the development of viable new products from traditionally discarded materials. Instances of up to 50 tonnes/acre of harvested sweet potatoes being discarded due to oversupply or shape standards justify this concern. Consequently, this work investigated the potentialof using a dried nutritional powder from sweetpotatoes as a feed supplement for livestock. Determination of the efficacy of this feed supplement without requiring live animal trials necessitated the development of in vitro testing methods, which were refined to allow small scale simulation of stomach and intestinal digestion in cattle using rumen fluid and pepsin treatments. In addition to determining the dry matter digestibility of animal feedstuffs, the method allowed simulation of the resultant digestive fluid, allowing further interrogation of the bioavailability of other compounds of interest. Both grass-fed and grain-fed cattle rumen fluid were used in separate trials comparing a standard cattle feedlot grain against the food waste supplement, as well as combinations of the feedlotgrain with 5, 10, 20, and 30% w/w of the food waste supplement. In the comparison, the food waste supplement was more digestible than the traditional feedstock, with an in vitro digestibility of 95.37 ± 1.18%versus 77.73 ± 1.71%. In the combined feed trials, grain-fed rumen digestibility did not vary significantly with addition of the food waste supplement (F4,9 = 0.336, P = 0.847). However, in the grass-fed rumen trial, a difference in the treatments was observed (F4,10 = 7.632, P> 0.004). Post hoc Tukey testing indicated a general increase in digestibility as the quantity of food waste supplement increased. This indicates that in terms of digestibility, the food waste-derived supplement could be readily added to existing rations without negative effect.