Brassica rapa L. supplementation improves milk production and antioxidant status via rumen microbe–metabolite interactions in periparturient dairy cows of the Tibetan Plateau

Abstract

Successfully navigating the periparturient period poses significant challenges for dairy cows in plateau environment. Brassica rapa L., a common crop in plateau regions, is rich in bioactive compounds and provides multiple benefits, including protection against altitude sickness, antioxidant effects, and immune regulation. This study investigated the effects of Brassica rapa L. supplementation on lactation performance, serum oxidative stress, and ruminal microbiota-metabolite interactions in periparturient dairy cows living at high altitudes. Thirty Holstein cows, all in their first pregnancy with similar milk yields, diet, and body weights, were randomly assigned to three groups: a Control (Con) group following NRC standards feeding, a Brassica rapa L. group (Bra) supplemented with 20 g / per cow / day of Bra, and an N-Carbamylglutamate (NCG) group received 20 g / per cow / day of NCG. The trial lasted 45 days. Milk production was recorded monthly, and milk fat and protein contents were determined from pooled samples collected during the final month. In addition, ruminal fluid and blood were collected on the first day after the experiment to analyse oxidative stress indicators, ruminal microbiota, and secondary metabolites. Brassica rapa L. significantly increased milk yield (March) and milk protein content, while both Bra and NCG groups showed elevated serum glutathione peroxidase and reduced malondialdehyde levels, indicating enhanced antioxidant capacity. 16S rRNA sequencing revealed that Bra supplementation enriched cellulose-degrading bacteria such as Fibrobacter, Treponema, and Prevotella, which were positively correlated with elevated levels of acetate, propionate, and butyrate in the rumen. Using LC-MS/MS metabolomics, it was showed that Bra upregulated metabolites like dehydroepiandrosterone sulfate and raffinose, and enriched arginine biosynthesis while downregulating arachidonic acid metabolism. Supplementation with NCG increased the abundance of Lachnospiraceae (e.g., Anaerovibrio, Coprococcus, Moryella), elevated levels of butyrate, and enhanced TCA cycle activity. Correlation analyses confirmed strong links between altered microbiota, metabolites, and host performance. These findings demonstrate that Brassica rapa L. and NCG can alleviate oxidative stress, enhance milk production, and improve energy and nitrogen metabolism in periparturient cows through targeted modulation of ruminal microbial and metabolic networks, offering potential for improving dairy cow resilience in plateau environments.