A. J. Kauffman and N. R. St-Pierre1
The Ohio State University Department of Animal Sciences
This study was conducted to clarify the relationship between urinary nitrogen (UN) excretion and concentration of milk urea N (MUN) to confirm whether this relationship is linear or suggests non-linearity, and to determine if there is a difference in the relationship between breeds. Eight multiparous cows (four Holstein, four Jersey) were fed four different diets in a 2 x 2 factorial arrangement of crude protein (CP) and neutral detergent fiber (NDF). Levels of crude protein were formulated for a low of 14% and a high of 18%, while NDF levels were formulated for a low of 30% and a high of 40%. No differences were found due to the level of NDF in the diet. Dietary crude protein had a significant effect on yields of milk, milk fat, and milk protein, as well as concentration of MUN. Crude protein also had a significant effect on the nitrogen (N) balance of the animals with effects seen in nitrogen intake, fecal and urinary N excretion, milk N yield, and apparent N digestibility. The relationship between UN and MUN was found to be linear over the range of MUN values observed and was found to be different for the two breeds.
1 For more information, contact at: The Ohio State University, 221A Animal Science Building, 2029 Fyffe Road, Columbus, OH 43210, 614-292-6507, Fax 614-292-1515, e-mail: st-pierre.8@osu.edu