The DDGS contain higher levels of protein, fat, and fiber compared with its original grains (Choi et al. 2009). Therefore, replacing a certain amount of feed ingredients with DDGS is economically sound when its nutrients are available to the animals (Alsuwaiegh et al. 2002). It has been well documented that fermented products provide more beneficial microbes, digestive enzymes, and bioactive metabolites to animals and thus beneficially improved the ADG (Jami et al. 2012). However, in the present study, dietary FS-DDGS addition did not affect the ADFI, ADG, and F:G of pigs, suggesting that the addition levels of 50–150 g/kg FS-DDGS does not affect pigs’ growth performance. One possible explanation is that a higher level of dietary FS-DDGS increased the dietary fiber level, and therefore negatively affected the nutrient availability to the animals. Another explanation is that high-fiber diet induced the growth of the visceral organs (Wenk, 2001) and secretion of digestive fluids (Agyekum et al. 2013), and therefore increased energy expenditure for maintenance rather than for catabolic metabolism (Nyachoti et al. 2000). The latter tended to be supported by the increased loin eye area and reduced bone percentage of pigs fed the diets with FS-DDGS. Therefore, our findings suggested that the FS-DDGS could be supplemented to diet of growing-finishing pigs up to 150 g/kg and partially replace grains.
Meat color affects the perception of freshness and is a key driving factor for customer purchase (Brewer et al. 2001). The pH value, color, and water holding capacity of meat indicate meat quality (Ahmed et al. 2016). The pH value of pork in the present study was within 5.3 to 5.7, indicating that it was under the optimal level (Warriss, 1982). In addition, the L* value decreased with the increase in dietary FS-DDGS level, suggesting the improvement in meat quality because the L* value is inversely correlated with the pH value of the muscle (Huff-Lonergan et al. 2002). In our study, dietary FS-DDGS addition decreased b* and L* values while increased a* value, suggesting a component of it might affect meat quality in pigs. In addition, lower drip loss was found in the FS-DDGS groups. Similarly, fermented ginkgo leaves also reduce drip loss value in broilers (Niu et al. 2017). It is well known that most water in the cell is held in myofibrils. The type of muscle fibers and the content of fat are likely to play a significant role in the drip loss (Yang et al. 2019). Since the FS-DDGS addition has no effect on the fat content of the muscles, the reason for the lower drip loss may be the difference in muscle fibers, but this needs further research. In general, dietary FS-DDGS addition ameliorated meat quality by decreasing drip loss and improving meat color and pH value of pork.
In addition, dietary FS-DDGS addition increased the contents of ash and crude protein in LD muscle in the present study. The higher ash content could be attributed to the fermentation process, which increases the availability of ash in the diet supplemented with FS-DDGS by reducing the level of anti-nutritional tannins and flavonoids that inhibit mineral absorption (Ahmed et al. 2016). Amino acids are the building blocks of proteins, and their composition and content represent protein quality. Furthermore, some amino acids play key roles in the aroma and flavor profiles of meat. For example, Arg, Leu, Ile, Val, Phe, Met, and His present a bitter taste; Glu and Asp present a pleasant fresh taste; and Gly, Ala, and Ser present a sweet taste (Lorenzo and Franco, 2012). In the present study, dietary FS-DDGS addition increased the contents of Pro in LD muscle, as well as Ala, Arg, Asp, Glu, Ile, Leu, Lys, Ser and Tyr in BF muscle. Previous study showed that proper industrial fermentation with beneficial microbes on feed ingredients could increase the contents of amino acids and improve the availability of dietary protein, thereby increasing nutrient value of pork (Vong et al. 2016). Taken together, dietary FS-DDGS addition could improve the quality and flavor of pork by improving the muscular contents of flavor amino acids.