Variation in urea kinetics associated with ruminant species, dietary characteristics, and ruminal fermentation: A meta-analysis

The objective of this meta-analysis was to quantitatively summarize variations in urea kinetics related ruminant species, diet composition, and ruminal fermentation. A database 31 studies measuring recycling were used derive 2 sets linear mixed-effects regression models. Study as a random intercept regressions weighted by 1 divided the standard error mean observation. Models compared, when appropriated, using concordance correlation coefficient, root estimated variance associated with study (?ˆs) (?ˆe) corrected Akaike information criterion values. From dietary standpoint, most response variables affected measures reflecting crude protein [(CP; e.g., N-NH3 or rumen-degradable (RDP)] energy content [e.g., total digestible nutrients (TDN), starch, pH]. Dietary CP, N-NH3, TDN typically had positive slopes on N entry rate (UER; g/d g/kg0.75), whereas starch TDN/RDP negative UER (g/kg0.75). On other hand, increasing increased gastrointestinal (GER; an opposite effect observed for RDP. Increasing RDP reduced returned ornithine cycle (ROC; g/kg0.75) Ruminal also reflected importance supplies. ammonia concentration significantly ROC (g/d anabolism (UUA; ROC:GER, UUA:GER, incorporation recycled into microbial relative urea. pH GER:UER ROC:GER ratios. Total slope UUA ratio (TDN:RDP) ratio, decreased UUA:GER N. Comparison among models revealed that species important explanatory variable affecting variables. However, whether these differences are intrinsic metabolism each due variation remains unclear. Understanding could lead improvements use efficiency diets formulating more precise low-N considering particularities species.