Study on effects of COS and RPAA on rumen fermentation,nutrient degradation,and antioxidant function of dairy cows under a low-protein diet by in vitro three-step method

GUO Yongmei; DU Juan; WANG Jialu; LI Jiarong; SONG Yan; ZHAO Yanli; GUO Xiaoyu; YAN Sumei

doi:10.13557/j.cnki.issn1002-2813.2025.22.001

Abstract：The experiment aimed to explore the effects of chitosan(COS)and rumen-protected amino acids(RPAA)on in vitro rumen fermentation,nutrient degradation rates,and antioxidant function of dairy cows under low-protein diets by the in vitro three-step method.A single-factor completely randomized design was adopted,and the assessment was conducted using a three-step in vitro rumen-stomach-intestine method combined with a in vitro batch culture system.Five treatment groups were established:Normal protein level group(17.4％,group CON),low protein level group(15.5％,group 15.5CP),low protein diet+1 500 mg/kg COS group(group 15.5C1500),low protein diet+RPAA group(group 15.5AA),and low protein diet+RPAA+1 500 mg/kg COS group(15.5AA1500 group),with six replicates in each group.Relevant indicators were measured 24 hours after in vitro culture.The results showed that compared with the group CON,the dry matter(DM)degradation rate was significantly decreased in group 15.5CP(P＜0.05).The crude protein(CP)degradation rate in group 15.5AA1500 was significantly higher than that in group 15.5CP(P＜0.05).Compared with the group CON,the pH value of groups 15.5CP,15.5AA,and 15.5AA1500 was significantly increased(P＜0.05),while the bacterial protein(BCP)content in groups 15.5CP and 15.5C1500 was significantly decreased(P＜0.05).The propionic acid content in groups 15.5C1500 and 15.5AA1500 was significantly higher than that in group 15.5CP(P＜0.05),and the total volatile fatty acid(TVFA)content in group 15.5CP was significantly lower than that in group CON(P＜0.05).The total superoxide dismutase(T-SOD)activity of rumen fluid in group 15.5AA1500 was significantly higher than that of group 15.5CP(P＜0.05),and the total antioxidant capacity(T-AOC)and 1,l-diphenyl-2-trinitrophenylhydrazine(DPPH)free radical clearance rate were significantly higher than those of the other groups(P＜0.05),the malondialdehyde(MDA)content was significantly lower than that of the group 15.5CP(P＜0.05).The study shows that the combined supplementation of RPAA and COS in a low-protein diet can effectively improve the nutrient degradation rate,modify the rumen fermentation pattern,and enhance the antioxidant capacity of rumen fluid in dairy cows.