Nitrogen excretion from beef cattle fed a wide range of diets compiled in an intercontinental dataset: a meta-analysis

Abstract

Manure N from cattle contributes to nitrate leaching, nitrous oxide and ammonia emissions. Measurement of manure N outputs on commercial beef cattle operations is laborious, expensive, and impractical; therefore, models are needed to predict N excreted in urine and feces. Building robust prediction models requires extensive data from animals under different management systems worldwide. Thus, the study objectives were to (1) collate an international dataset of N excretion in feces and urine based on individual observations from beef cattle; (2) determine the suitability of key variables for predicting fecal, urinary, and total manure N excretion; (3) develop robust and reliable N excretion prediction models based on individual observation from beef cattle consuming various diets. A meta-analysis based on individual beef data from different experiments was carried from a raw dataset including 1,004 observations from 33 experiments collected from 5 research institutes in Europe (n = 3), North America (n = 1), and South America (n = 1). A sequential approach was taken in developing models of increasing complexity by incrementally adding significant variables that effected fecal, urinary, or total manure N excretion. Nitrogen excretion was predicted by fitting linear mixed models with experiment as a random effect. Simple models including dry matter intake (DMI) were better at predicting fecal N excretion, than those using only dietary nutrient composition or BW. Simple models based on N intake performed better for urinary and total manure N excretion than those based on DMI. A model including DMI and dietary component concentrations led to the most robust prediction of fecal and urinary N excretion, generating root mean square prediction errors as a percentage of the observed mean values of 25.0% for feces and 25.6% for urine. Complex total manure N excretion models based on BW and dietary component concentrations led to the lowest prediction errors of about 14.6%. In conclusion, several models to predict N excretion already exist, but the ones developed in this study are based on individual observations encompassing larger variability than the previous developed models. In addition, models that include information on DMI or N intake are required for accurate prediction of fecal, urinary and total manure N excretion. In the absence of intake data, equations have poor performance as compared to equations based on intake and dietary component concentrations.

Models to predict nitrogen excretion from beef cattle fed a wide range of diets compiled from South America

“…An additional screening was carried out to identify improbable observations. Observations where N excretion in urine, expressed in percentage of N intake, where below 10% or above 60% were also excluded using the range of values found in several reports in the literature as criteria ( Waldrip et al., 2013 ; Dong et al., 2014 ; Angelidis et al., 2019 ; Bougouin et al., 2022 ). This procedure resulted in the exclusion of 75 observations.…”

“…S1 ). The factor of 1.5 was used in constructing markers to identify outliers ( Bougouin et al., 2022 ). As a result, we removed 14, 7, and 14 outliers for fecal, urinary, and manure N excretions, respectively.…”

“…With these models, beef producers can predict N excretion in beef cattle and evaluate the N use efficiency in their operations. A variety of models exist in the literature to predict nitrogen excretion in beef cattle ( Waldrip et al., 2013 ; Dong et al., 2014 ; Reed et al., 2015 ; Bougouin et al., 2022 ). These models were developed using animals and diets in temperate conditions typical of Europe and North America.…”

“…However, they might not fully represent dietary conditions, animal genotypes, and management approaches adopted by beef producers in tropical conditions encountered in South America ( Congio et al., 2023 ), all of which are expected to influence N excretion. Bougouin et al. (2022) recently conducted a meta-analysis to develop models to predict N excretion in beef cattle using an intercontinental database.…”

Perspectives on the Fate of Absorbed Nitrogen in Dairy Farms

“…During the storage of feces and urine in dairy farm, N could be rapidly converted to ammonia and emitted into the air, while ammonium and nitrate as the main inorganic forms of N in the manure phase would leach into the soil and groundwater, and a large amount of Nitrous oxide (N2O) that is a potent greenhouse gas can be produced through nitrification and denitrification (King et al, 2021;Bougouin et al, 2022a). The excess N in cattle manure and urine would lead to serious environmental and social problems, such as eutrophication of lakes and other water bodies, enhancement of PM2.5, aggravation of greenhouse gas emission, destruction of stratospheric ozone, deterioration of soil and surface water due to the increased acidity of precipitation, and aggravation of asthma (Wolfe and Patz, 2002;Bougouin et al, 2022b). The production of N2O is determined by the concentration of a variety of excreta (e.g., urea, purine derivatives, creatine and creatinine) while urinary N is dominant (Dijkstra et al, 2013;Wang et al, 2015;Zhao et al, 2019).…”