Research and Reviews 1999

Special Circular 168-99

Estimation of Microbial Nitrogen Flow to the Duodenum of Cattle Based on Dry Matter Intake and Diet Composition

B. S. Oldick, J. L. Firkins¹, and N. R. St-Pierre
The Ohio State University Department of Animal Sciences

Abstract

Predictions of microbial nitrogen (N) flow to the duodenum based on the intake of net energy of lactation (NEL; megacalories per day) were improved compared with the equation in the current National Research Council’s Nutrient Requirements of Dairy Cattle (NRC, 1989). However, a procedure based on multiple regression using terms for dry matter intake (DMI) and dietary concentrations of crude protein, neutral detergent fiber (NDF), and concentration of forage in the diet resulted in the following equation:

Microbial N flow, g/day = 16.1 + (22.9 x DMI, kg/d) — (0.365 x DMI2) — (1.74 x NDF, % of DM).

¹ For more information, contact at: The Ohio State University, 223 Animal Science Building, 2029 Fyffe Road, Columbus, OH 43210, 614-688-3089, Fax 614-292-1515, e-mail: firkins.1@osu.edu