The effect of concentration and form of dietary nitrogen on the utilization and excretion of nitrogen by lactating dairy cows

Abstract

Three total mixed rations containing differing sources and levels of protein were fed to 18 lactating cows in a 3 × 3 Latin square design with the objective of quantitating nitrogen losses for specific feeding regimes. Feeding a total mixed ration containing 12.3% crude protein reduced the amount of nitrogen excreted and increased the proportion of dietary nitrogen secreted in the milk. The diet supplemented with corn gluten meal resulted in high blood urea nitrogen levels and higher losses of nitrogen in the urine. It was concluded that diet formulation impacts on nitrogen wastage.

Nitrogen utilisation by dairy cows fed diets differing in crude protein level with a deficit in ruminal fermentable nitrogen

“…The differences in the amounts of nitrogen ingested or apparently digested between the different diets were greater than the differences in the amounts of protein recovered in the milk. This was shown by a decrease in the ratio of nitrogen in milk proteins to ingested nitrogen with increasing CP levels in the diet, confirming the results of Castillo et al [5], Dinn et al [8], Fisher et al [10], Peyraud et al [18], Van Vuuren et al [26], Volden [31] and Wright et al [32]. Consequently, the amount of nitrogen released in the urine increased with increasing CP supply.…”

“…These high levels of nitrogen secretion in the milk represent a great interest for decreasing nitrogen excretion in the environment (faeces and urine). Many trials have recently studied the utilisation of feed nitrogen by dairy cows; the values observed are from 0.24 to 0.30 of nitrogen ingested recovered in milk by Castillo et al [4,5]; from 0.29 to 0.33 by Fisher et al [10] and from 0.25 to 0.34 by Kebreab et al [13]. In these trials, the levels of crude protein in the diets were between 12.3% DM and 19.0% but no indication of the energy supplies were available.…”