Study on the effects of low protein diet on nitrogen utilization and urine metabolites in dairy cows

Abstract

Abstract Background Dietary protein level and supplementation of rumen-protected lysine (RPLys) and rumen-protected methionine (RPMet) on nitrogen utilization and urine metabolites of dairy cows are very important in improving dairy production. Results The results showed that the cows in LP group had higher DMI than the HP group after 30d (P < 0.001) and 90d (P = 0.047). The nitrogen intake from the feed in the LP group was lower than HP after 30d (P = 0.014), 60d (P < 0.01), and 90d (P < 0.01). Compared to the HP group, the total nitrogen excretion was lower in the LP group after 30d (P = 0.003), 60d (P < 0.001), and 90d (P < 0.001). Cows fed with LP had a trend of higher nitrogen digestibility after 90d (P = 0.052) than cows fed with HP. The LP treatment increased the nitrogen utilization efficiency after 30d (P = 0.036), 60d (P = 0.023), and 90d (P = 0.021) when compared with HP. A total of 503 metabolites were detected in the urine of cows. Compared with HP, the LP group had 263 metabolites that were down-regulated and 240 metabolites that were up-regulated. Conclusion Feeding dairy cows with a low-protein diet supplemented with amino acids can decrease nitrogen excretion, improve nitrogen utilization efficiency, and show effects on protein digestion and absorption, energy supply and rumen microbiota through the regulation of L-tryptophan and L-alanine.