Influence of Dietary and Ruminal Factors on Microbial and Non-Microbial Nitrogen Flows to the Small Intestine in Lactating Dairy Cows: A Meta-Analysis
Year: 2025
Type: review
Study designs: Systematic Review, Meta-Analysis
Abstract: Improving nitrogen efficiency in dairy cattle requires a better understanding of the dietary and ruminal factors that regulate nitrogen partitioning. This meta-analysis evaluated the effects of ruminal pH and dietary characteristics on microbial nitrogen (MN), non-microbial non-ammonia nitrogen (NANMN), and NAN flows to the small intestine in lactating cows. A dataset was assembled from 44 peer-reviewed in vivo studies (163 data points), with dietary intake and ruminal variables standardized across trials. Mixed linear models were developed for each N fraction, and the relative contribution of each predictor to the explained variance was assessed using semipartial coefficients of determination (pR2). Efficiency of microbial protein synthesis (EMPS), rumen undegraded protein intake (RUPI), and organic matter truly digested in the rumen (OMTDR) were the most relevant predictors of NANMN and NAN. Although the ruminal pH itself was not statistically significant in the models, the dietary components that influenced pH, starch concentration, physically effective fiber, and RUP supply were strongly associated with nitrogen flow profiles. Nitrogen utilization was not affected by ruminal pH, but rather by the combination of fermentable substrates and the supply of rumen-degradable and undegraded protein.
Source: Dairy
DOI: 10.3390/dairy6060066
Authors: Danilo D. Millen, Gercino F. Virgínio, Fernanda F. Alves, Charles G. Schwab, Sergio Calsamiglia
Language: English
Subfield: Agronomy and Crop Science
Domain: Life Sciences
SDG: Zero hunger
Open Access status: gold
Estimated APC paid: $1,448
Awards: G2823776494, G7573879127
OpenAlex ID: W4415992851