Effect of hepatic urea recycling on nitrogen use efficiency in ruminants: a meta-analysis

• Grant number: 25/05103-0
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: June 01, 2025
• End date: May 31, 2026
• Field of knowledge: Agronomical Sciences - Animal Husbandry - Animal Nutrition and Feeding
• Principal Investigator: Vinícius Carneiro de Souza
• Grantee: Beatriz Kinue Shiraishi
• Host Institution: Faculdade de Zootecnia e Engenharia de Alimentos (FZEA). Universidade de São Paulo (USP). Pirassununga , SP, Brazil

Abstract

The objective of this project is to evaluate, through a meta-analysis, the role of hepatic urea recycling in nitrogen (N) excretion and utilization efficiency using a database built from a systematic literature review of studies that assessed urea kinetics in beef cattle, dairy cattle, and sheep. To this end, a pre-existing database will be used, comprising 124 treatment means from 31 studies (sheep = 9, beef cattle = 12, dairy cattle = 10) that evaluated urea kinetics in ruminants.Additionally, a new systematic literature review will be conducted to identify new studies published since 2020 in the PubMed, Google Scholar, and ScienceDirect databases. The keywords used will be urea recycling, urea kinetics, nitrogen metabolism, sheep, beef cattle, and dairy cattle. These keywords will be used individually or in various combinations during the search process.The contribution of diet composition, ruminal parameters, experimental variables such as feed intake and digestibility, and urea kinetics to the observed variation in N excretion in feces, urine, and total excretion, as well as N retention and the proportion of retained N relative to intake, will be assessed using meta-analysis techniques.The models will be derived using mixed-effects linear regression, considering a random intercept for the study effect, with the use of R software. The normality of the residuals will be verified at each stage of the model derivation process through residual plots. The models will be tested for their predictive ability on new observations using the Monte Carlo cross-validation technique.It is expected that the results of this meta-analysis will elucidate the potential benefits of N recycling for improving N utilization efficiency in production ruminants.