Replacing dietary alfalfa hay with nettle benefits rumen ph balance and microbiota in rumen and feces with minimal effects on performance and digestibility in dairy cows

Abstract

This study investigated the effects of replacing alfalfa hay (AH) with nettle hay (NH) in total mixed rations (TMR) of lactating cows, focusing on lactation performance, nutrient digestibility, and rumen and fecal microbial community structure. Twenty multiparous Holstein cows with similar days in milk (DIM = 91 ± 8), milk production (43 ± 3 kg/d), milk fat (3.81 ± 0.39%), and milk protein (3.05 ± 0.19%) were randomly assigned to two groups (n = 10) in a single-factor test design. Groups fed AH or NH had free access to water for 80 days, including a 20-day pre-feeding period. The results revealed no significant differences in nutrient intake, apparent digestibility, milk yield and composition, and feed efficiency between groups. However, the NH group displayed a decrease in the percentage of milk fats (NH = 3.82%, AH = 4.16%) and proteins (NH = 3.16%, AH = 3.31%). Additionally, the NH group exhibited higher rumen pH (NH = 6.34, AH = 6.10) and isovalerate concentration (NH = 2.46, AH = 1.92 mmol/L). Amplicon sequencing revealed differences in rumen fluid and feces microbiota between AH and NH groups. In rumen, the relative abundance of opportunistic pathogens such as Burkholderiaceae was 68.18% lower in NH than AH. At the genus level, the NH group had lower relative abundance of Ruminococcaceae V9D2013 species, which positively correlated with milk fat content. In feces, the relative abundances of Bacteroidetes and Verrucomicrobia were significantly lower in the NH group. At the family level, the relative abundances of Lachnospiraceae and Veillonellaceae were 10.45% and 193% higher, respectively, in the NH group. These differences were also observed at the genus level. Collectively, the findings suggest that the NH diet positively affected gastrointestinal function and increased the abundance of beneficial microbiota. In conclusion, replacing AH with NH positively affects rumen pH and gastrointestinal microbiota in dairy cows with negligible effects on milk yield and nutrient digestibility, but these effects need to be further investigated.