Wednesday, August 24, 2011

Improving the Efficiency of Nitrogen (N) Utilization

Profitable milk production depends on efficient use of dietary protein. The target should be for 30% of Total N ingested to be converted to Productive N and for the Productive N/Urinary N ratio to be greater than 100%.

Typically only 25% of N intake is incorporated into milk protein - in other words 75% is excreted in the urine and feces. Fecal N is relatively constant, thus the extra N consumed by the cow is secreted in the urine which is the most volatile form. Olmos, Colmenero and Broderick found that as cows consume more N, the N secreted in the milk as well as the N secreted in the feces was fairly constant. On the other hand, the N excreted in the urine increased linearly in relation to the intake. The net effect was that the efficiency of N utilization decreased from 36 to 25%. Maximizing N efficiency is not only good for the environment; it is also good for the cow's energy status. It takes 7.2 Kcal of Metabolizable Energy per gram of excess N to convert to urea.

Accurately balancing the rations for Amino Acids will further improve the efficiency of N utilization by lowering N inputs while maximizing milk protein synthesis.

The new CNCPS v6 (incorporated in the AMTS, NDS and other commercial software programs) includes reports that help us monitor how efficient N utilization is in a particular situation.

Fecal (lbs) 107
Urine (lbs) 47
Total Manure (lbs) 154
Fecal N (g) 248
Urine N (g) 184
Total Manure N (g) 431
Productive N:Total N 0.36:1 Productive N/Total N > 30%
Productive N:Urinary N 1.29:1 Productive N/Urinary N > 100%
Manure N:Total N 0.64:1

Efficiency of N Utilization (Olmos Colmenero and Broderick, 2006)