Utilization of fruit and vegetable wastes as an alternative renewable energy source in ruminants’ diet

The utilization of food processing discards would not only contribute towards waste reduction and feed security but also would reduce costs associated with the feedstuff import. These byproducts have been repetitively shown to stimulate animals’ performance while being beneficial to the overall health of animals. The purpose of present study was to determine the nutritional value of apple, carrot, and pomegranate pomace using three-step methods of digestion and gas production test along with determination of the best digestion model. For this purpose, two ruminally fistulated wethers (48 ± 2 kg) were used. The amount of in vitro gas production of experimental diets’ dry matter (DM) was documented at 2, 4, 6, 8, 12, 24, 48, 72, and 96 h of incubation. Obtained data from different hours of gas production were used to evaluate the digestion models. Pomegranate pomace produced the least cumulative in vitro gas in all incubation times while carrot pomace produced the most (P < 0.05). Estimated parameters of organic matter digestibility (OMD), metabolizable energy (ME), net energy for lactation (NEl), and short-chain fatty acids (SCFA) were highest for carrot and apple pomace, while pomegranate pomace had the lowest values (P < 0.05). Our results for ruminal and post ruminal DM digestibility showed that carrot pomace and barley grain had higher digestibility compared with other groups. Furthermore, results showed that pomegranate had lower digestibility in all parts of the total tract (P < 0.05). Total tract digestibility of protein was highest (88.6%) and lowest (82.9%) for barley grain and pomegranate pomace, respectively (P < 0.05). The non-lagged exponential (model I), the lagged exponential (model II), the Gompertz (model III), and the generalized Mitscherlich (model IV) models were evaluated for describing the results of in vitro gas production. Correspondingly, the Gompertz model with high R and low MSE was the best digestion model. In conclusion, food processing discards could potentially be utilized as alternative feedstuff in the ruminants’ diet with no adverse effect on animals’ performance. Graphical abstract: [Figure not available: see fulltext.]