Effect of Different Moisture Absorbents on Silage Fermentation Quality of Wet Potato Pulp

Introduction Using agricultural-industrial waste is one way to overcome the shortage of animal feed. Potato is one of the most important products in the world after rice, wheat and maize. Potato pulp is a by-product which remains after extraction of starch, and can be used as animal feed. Because of the high moisture content of the potato pulp, silage is the best way to maintain it. However, its high moisture content leads to inappropriate ensilage. Adding of moisture absorbents (MA) not only reduce the effluents, but also improve the silage quality. Materials with high content of cell wall are suitable candidates to be used as MA. Agro-industrial co-products including raisin wastes and pomegranate seed pulp have high cell wall and no report was found for their usage as MA. The purpose of this study was to assess the effect of different absorbents on potato pulp silage fermentation quality.Materials and Methods Fresh potato pulp was obtained from Alvand potato processing company (Hamedan, Iran). After transfer, the potato pulps were immediately ensiled with MAs including wheat bran, raisin pedicles, rejected raisins, pomegranate peel, wheat straw and raisin rachis. The treatments were: 100% potato pulp (control), 80% potato pulp and 20% wheat bran, 80% potato pulp and 20% raisin pedicles, 71% potato pulp and 29% rejected raisin, 80% potato pulp and 20% pomegranate peel, 80% potato pulp and 20% wheat straw and 80% potato pulp and 20% rachis. After 74 days, the silos were opened for investigation. Chemical composition (i.e., dry matter, crude protein, neutral detergent fiber, acid detergent fiber, Fleig point, pH and lactic acid concentration) were determined. In vitro gas production was used to assess fermentation parameters of treatments. Therefore, volume of gas production after 24 hours of incubation, rate of gas production, asymptotic gas production, lag phase, organic matter digestibility, metabolizable energy, partitioning factor, microbial biomass and short chain fatty acid concentration were determined. All measurements were carried out with four replications. Statistical analysis was carried out in completely randomized design using SAS (version 9.2). Results and Discussion Results showed that the addition of absorbent to potato pulp silage significantly (P˂0.05) increased dry matter, content of the cell wall, organic matter and Fleig point in some treatments. Fleig point is an indicator of silage quality. The treatment including rejected raisin showed the highest value of Fleig point (139.8 vs. 55.53 for control). The lowest ammonia concentrations were detected in treatments containing rachis, pedicles and pomegranate peels which can be attributed to the presence of tannin in these absorbents. Tannins reduce the proteolysis that lowers the ammonia concentration. The concentrations of lactic acid were higher in rejected raisin (3.734 g lactic acid/ kg DM) and pomegranate seed pulp (3.612 g lactic acid/kg DM) and the minimum value was observed in control (0.471 g lactic acid/ kg DM). The higher concentration of lactic acid shows the better quality of silage and among other fatty acids has the greater effect on pH of silage. Addition of different absorbents reduced true organic matter digestibility. Apparent organic matter digestibly was not consistent with reported value for true organic matter digestibility. This could be due to the method of measuring of former. In this method the residue is contaminated with microbial debris which overestimates the organic matter digestibility. After 144 hours of incubation gas production was reduced in treatments with absorbents. Rate of gas production in silage with rejected raisin was significantly (P˂0.05) higher than other treatments. Lag time observed only in control and wheat bran treatments, whereas the lag time in other treatment was zero. Partitioning factor in raisin pedicles, pomegranate peel and raisin rachis was higher than other treatments (3.05, 3.35 and 3.01). The higher value of partitioning factor shows the better quality of feedstuff and reveals that more fermented organic matter directed towards microbial biomass rather than production of volatile fatty acids. Conclusion Because of high moisture content of potato pulp, it is suggested to ensiling this by-product for using as ruminant feedstuff. In this study, rejected raisin was the best moisture absorbent. The results showed that treatments containing rejected raisin, pomegranate peel, pedicles and rachis were suitable absorbent in ensilage process because of lower pH, higher lactic acid production and better quality of silage, respectively.