Effects of long-term feeding of Achyranthes japonica Nakai extractas a supplement to diets with different protein levels diets on the growth performance and meat quality characteristics of growing-fattening pigs

Reductions in dietary protein and the supplementation of diets with feed additives have become two practical strategies in swine production to reduce costs and promote pig growth and health. This study was conducted to evaluate the effects of long-term feeding of Achyranthes japonica Nakai extract (AJE) combined with different dietary protein levels on growth performance, nutrient digestibility, blood parameters, fecal microbiota, fecal noxious gas emissions, meat quality, and carcass grade in growing-fattening pigs. In total, 144 crossbred [Duroc x (Yorkshire x Landrace)] growing pigs with average initial body weight (BW) of 23.77 +/- 1.65 kg were used in a 16-week feeding experiment. The pigs were randomly sorted into one of six dietary treatments in a 2 x 3 factorial arrangement with two levels of dietary protein-high crude protein (HCP) vs. low crude protein (LCP), each without (0 g/kg) or with two doses of AJE (0.5 g/kg and 1 g/kg) based on the BW and sex [four pigs per pen (two barrows and two gilts); six pens per treatment]. All samples were taken at the end of the growing (week 6) and fattening (week 16) phases. Growth performance indices were also assessed in the middle of the fattening phase (week 11). The addition of both dosage of AJE improved the average daily gain (ADG) throughout the experimental period. Similarly, the ADG was higher in pigs fed the HCP diet than in those fed the LCP diet during weeks 6 and 11 and throughout the experimental period. At weeks 6 and 16, positive effects on digestibility, blood profiles, fecal microbial population, fecal gas emission concentrations, and the water holding capacity of meat were observed in pigs fed AJE-supplemented diets. The pigs fed the HCP diet had higher nitrogen digestibility, blood total protein, serum growth hormone, and insulin-like growth factor-1 at both weeks 6 and 16. Furthermore, pigs fed the HCP diet had higher blood urea nitrogen concentrations and carcass weights at week 16, and lower fecal Escherichia coli counts at week 6. Additionally, lower con-centrations of fecal ammonia and total mercaptans were observed at weeks 6 and 16, respectively. In summary, AJE and high dietary crude protein level improved growth performance, nutrient digestibility, blood parameters, fecal microbiota, fecal noxious gas emission, and meat quality but no interactive effects between protein level and AJE were observed.