A revised representation of urea and ammonia nitrogen recycling and use in the Molly cow model

Abstract

Accurately predicting nitrogen (N) digestion, absorption, and metabolism will allow formulation of diets that more closely match true animal needs from a broad range of feeds, thereby allowing efficiency of N utilization and profit to be maximized. The objectives of this study were to advance representations of N recycling between blood and the gut and urinary N excretion in the Molly cow model. The current work includes enhancements (1) representing ammonia passage to the small intestine; (2) deriving parameters defining urea synthesis and ruminal urea entry rates; (3) adding representations of intestinal urea entry, microbial protein synthesis in the hindgut, and fecal urea-N excretion; and (4) altering existing urinary N excretion equations to scale with body weight and adding purine derivatives as a component of urinary N excretion. After the modifications, prediction errors for ruminal outflows of total N, microbial N, and nonammonia, nonmicrobial N were 29.8, 32.3, and 26.2% of the respective observed mean values. Prediction errors of each were approximately 7 percentage units lower than the corresponding values before model modifications and fitting due primarily to decreased slope bias. The revised model predicted ruminal ammonia and blood urea concentrations with substantially decreased overall error and reductions in slope and mean bias. Prediction errors for gut urea-N entry were decreased from 70.5 to 26.7%, which was also a substantial improvement. Adding purine derivatives to urinary N predictions improved the accuracy of predictions of urinary N output. However, urinary urea-N excretion remains poorly predicted with 69.0% prediction errors, due mostly to overestimated urea-N entry rates. Adding representations of undigested microbial nucleic acids, microbial protein synthesized in the hindgut, and urea-N excretion in feces decreased prediction errors for fecal N excretion from 21.1 to 17.1%. The revised model predicts that urea-N entry into blood accounts for approximately 64% of dietary N intake, of which 64% is recycled to the gut lumen. Between 48 and 67% of the urea recycled to the gut flows into the rumen largely depending on diet, which accounts for 29 to 54% of total ruminal ammonia production, and 65 to 76% of this ammonia-N is captured in microbial protein, which represents 17% of N intake. Based on model simulations, feeding a diet with moderately low crude protein and high rumen-undegradable protein could increase apparent ruminal N efficiency by 20%.

Urea supplementation in rumen and post-rumen for cattle fed a low-quality tropical forage

“…Concurrently, the urinary N losses decrease as an attempt to spare N (11) . There is also a direct relationship between dietary N intake and urinary N excretion, whereby increasing dietary N will increase urinary N excretion and consequently the N wasted (12) .…”

Metabolismo en rumiantes y su asociación con analitos bioquímicos sanguíneos

“…La digestión fermentativa es anaeróbica (Kittelmann et al, 2013;Yazdi et al, 2016), por lo que el C3H3O3 funciona como captador de electrones, para generar NAD + y ATP, retirando NADH+H + (Górka et al, 2017). Los ácidos grasos volátiles (AGV): acético (CH 3 -COOH), propiónico (CH 3 -CH 2 -COOH) y butírico (CH3-CH2-CH2-COOH) son los principales productos terminales de la digestión fermentativa (Aydin et al, 2017;Li et al, 2019 a ); son absorbidos a través de la pared del rumen e incorporados a la circulación mediante la vena porta (Resende Jr et al, 2019). Representan entre el 70-80% del combustible energético del rumiante (Mikołajczyk et al, 2019).…”

“…Fuente: información sintetizada de (Gebreegziabher, 2016) La Microbiota Ruminal Proteolítica y la Fermentación Anaeróbica Los componentes proteicos suministrados en la dieta son fermentados por bacterias proteolíticas Bacteroides amylophylus, Bacteroides ruminicola, y algunas cepas de Butyrivibrio fibrisolvens (García et al, 2014), mediante sus proteasas microbianas, liberando péptidos (Alves et al, 2014;Rostom y Shine, 2018). Estos son absorbidos por el microorganismo, donde las peptidasas hidrolizan los enlaces peptídicos, liberando aa, utilizados para traducir proteínas propias o catabolizarlos para liberar energía (Li et al, 2019 b ;Silva et al, 2016). El producto final es el NH3 (Khezri et al, 2016;Carvalho et al, 2019), que sirve como sustrato de nitrógeno para las bacterias (Valente et al, 2016).…”

“…La degradación del alimento se realiza principalmente por digestión fermentativa, llevada a cabo por microorganismos presentes en el rumen (Ginane et al, 2015;Wallace et al, 2017). Las moléculas resultantes de la fermentación ruminal son aprovechadas para satisfacer los procesos fisiológicos del animal (Kittelmann et al, 2013;Li et al, 2019 a ). La cuantificación de los analitos bioquímicos en el plasma y/o suero, otorgan una aproximación al metabolismo nutricional (García et al, 2015); además confieren información sobre alteraciones y ajustes homeostáticos (Moyano et al, 2018).…”

ASAS-NANP SYMPOSIUM: RUMINANT/NONRUMINANT FEED COMPOSITION: Challenges and opportunities associated with creating large feed composition tables

“…Historically, the information provided by feed composition tables have been widely used to assist nutritionists in diet formulation tasks and are also used as tools to instruct students on the nutrient composition of different types of feeds and diet formulations. Similarly, feed composition datasets (used to construct feed composition tables) are widely used for developing and evaluating nutritional models ( Rumburg et al, 2008 ; Cemin et al, 2019 ; Li et al, 2019 ).…”