Excretion of nitrogen (N) from cattle within crop‐livestock systems is an important component of nutrient cycling, but measuring fecal and urinary N excretion in grazing cattle is a difficult and time consuming task. Nutritional models are available to estimate feed utilization and have been used to predict N excretion in grazing cattle. Using the Large Ruminant Nutrition Model, we predicted N losses from mature pregnant beef cows and growing beef heifers from compositional analysis of cover crop mixes grown in central South Dakota. All of the mixes used contained crude protein (CP) concentrations greater than cattle requirements. Estimates of both total fecal and urinary N excretion were greater for cows than heifers due to the greater BW and N intake of cows, however, the proportion of total N intake excreted in the feces was not predicted to differ between cattle maturities. Urinary excretion of N was predicted to be less for heifers, both when expressed as lb/d of N excreted or as a percentage of N intake. When accounting for potential stocking rate differences, it was predicted that slightly less urinary N excretion per acre could be expected by grazing younger cattle that utilize some N for growth compared to a mature animal.
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South Dakota State University
Copyright © 2013 South Dakota State University
Grings, E.E.; Sackey, A.; Hansen, M.; Owens, V.; Beck, D.; and Sexton, P., "Nitrogen Excretion from Beef Cattle for 6 Cover Crop Mixes as Estimated by a Nutritional Model" (2013). South Dakota Beef Report, 2013. 5.