Effects of dietary SID Lys levels on growth performance, carcass traits, muscle composition, blood biochemistry, and colonic volatile fatty acids in growing Ningxiang pigs

The purpose of this study was to explore the effects of changing standardized ileal digestible (SID) Lys levels in the diet on growth performance, carcass traits, meat quality, blood biochemical indices, and colonic volatile fatty acid levels of Ningxiang pigs, in order to determine their optimal SID Lys requirement. A total of 164 castrated Ningxiang pigs (days of age 135 ± 5and initial body weight of 35.57 ± 0.56 kg) were randomly divided into 5 dietary treatments with SID Lys levels of 0.50%, 0.60%, 0.70%, 0.80%, and 0.90%, respectively. Each treatment had 5 replicates with 6 to 7 pigs per replicate, and a feeding trial lasted for 45 d. Results showed that reducing dietary SID Lys from 0.50% to 0.90% did not affect final body weight (FBW), average daily gain (ADG), the ratio of feed to gain (F:G), and carcass traits ( P > 0.05). The 0.50% Lys group exhibited a significantly higher proportion of n-3 polyunsaturated fatty acids (PUFA) and a lower n-6/n-3 PUFA ratio in the longissimus dorsi ( P < 0.05), the proportion of saturated fatty acids (SFA) in the soleus was also higher compared with the 0.90% group ( P = 0.038). In the 0.70% group, the levels of essential, non-essential, umami, and total amino acids in the longissimus dorsi were significantly increased ( P < 0.05) while essential amino acid levels in the soleus were significantly higher in the 0.50% group. Additionally, blood urea nitrogen level was significantly reduced ( P = 0.026) and colonic butyrate and total volatile fatty acid contents were significantly increased in the 0.50% group compared with the 0.70% group ( P < 0.05). In conclusion, dietary SID Lys levels significantly influenced meat quality, blood biochemical indices, and colonic volatile fatty acids in Ningxiang pigs; however, reducing dietary SID Lys to 0.50% did not adversely affect their growth performance or economic traits.