Effect of dietary protein concentration and forage type on nitrogen metabolism and nutrient flux across the portal drained viscera and the liver in lactating dairy cows

摘要

With regard to daily cow nutrition, past efforts have focused on maximising milk output, rather than feed conversion efficiency. More recently, attention has reverted to the efficiency of milk production, and in particular dietary nitrogen (N) utilisation due to increasing concerns regarding nitrogenous emissions from dairy cattle. The contribution of dairy production to environmental pollutants, particularly nitrous oxide and ammonia, is an issue of increasing concern. Current feed prediction schemes concerning metabolisable protein are limited due to an oversimplification of post-absorptive events. There are few recent reliable data on the efficiency of converting dietary N into milk protein and there is still much variation seen between differentstudies (Hristov and Ropp, 2003; Lee et al, 2009). The present results are from a larger study concerned with describing the absoiption and metabolism of nutrients and metabolites by the splanchnic tissues in lactating dairy cows in response to vaiyingamounts of absorbable protein and two forage types.