92919751080ff286c31b34eda953bea4 dairy-06-00066-v2.pdf 6333cde315017a8d00599a40d2b0d21e9dcb6363 dairy-06-00066-v2.pdf 076a31fd485a884cd3952f9d2ba64ebbba623ecd8505c66d5bbd5cc74d408d9d dairy-06-00066-v2.pdf Title: Influence of Dietary and Ruminal Factors on Microbial and Non-Microbial Nitrogen Flows to the Small Intestine in Lactating Dairy Cows: A Meta-Analysis Subject: 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. Keywords: microbial protein synthesis; nitrogen utilization; rumen metabolism Author: Danilo D. Millen, Gercino F. Virgínio, Jr., Fernanda F. Alves, Charles G. Schwab and Sergio Calsamiglia Creator: LaTeX with hyperref Producer: pdfTeX-1.40.25; modified using OpenPDF 1.4.2 CreationDate: Mon Nov 17 10:18:35 2025 CET ModDate: Mon Nov 17 10:26:53 2025 CET Custom Metadata: yes Metadata Stream: no Tagged: no UserProperties: no Suspects: no Form: none JavaScript: no Pages: 10 Encrypted: no Page size: 595.276 x 841.89 pts (A4) Page rot: 0 File size: 245020 bytes Optimized: no PDF version: 1.7 name type encoding emb sub uni object ID ------------------------------------ ----------------- ---------------- --- --- --- --------- HWRWWM+URWPalladioL-Ital Type 1 Custom yes yes yes 74 0 KRSZUN+URWPalladioL-Bold Type 1 Custom yes yes yes 75 0 WULJEY+VnURWPalladioL Type 1 Custom yes yes yes 76 0 MMMJVQ+URWPalladioL-Roma Type 1 Custom yes yes yes 77 0 RFLZJB+CMR10 Type 1 Builtin yes yes yes 140 0 URYLRZ+URWPalladioL-BoldItal Type 1 Custom yes yes yes 151 0 FXXUVH+CMSY10 Type 1 Builtin yes yes yes 166 0 Jhove (Rel. 1.28.0, 2023-05-18) Date: 2026-02-13 03:08:45 CET RepresentationInformation: dairy-06-00066-v2.pdf ReportingModule: PDF-hul, Rel. 1.12.4 (2023-03-16) LastModified: 2026-02-12 13:07:25 CET Size: 245020 Format: PDF Version: 1.7 Status: Well-Formed and valid SignatureMatches: PDF-hul MIMEtype: application/pdf PDFMetadata: Objects: 312 FreeObjects: 1 IncrementalUpdates: 0 DocumentCatalog: ViewerPreferences: HideToolbar: false HideMenubar: false HideWindowUI: false FitWindow: true CenterWindow: false DisplayDocTitle: false NonFullScreenPageMode: UseNone Direction: L2R ViewArea: CropBox ViewClip: CropBox PrintArea: CropBox PageClip: CropBox PageLayout: SinglePage PageMode: UseNone Outlines: Item: Title: Introduction Item: Title: Materials and Methods Item: Title: Results Item: Title: Discussion Item: Title: Conclusions Item: Title: References Info: Title: Influence of Dietary and Ruminal Factors on Microbial and Non-Microbial Nitrogen Flows to the Small Intestine in Lactating Dairy Cows: A Meta-Analysis Author: Danilo D. Millen, Gercino F. Virgínio, Jr., Fernanda F. Alves, Charles G. Schwab and Sergio Calsamiglia Subject: 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. 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