Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 7/10/2006
Publication Date: 7/10/2006
Citation: Huhtanen, P., Broderick, G.A., Russell, J.B. 2006. Challenges in utilization of high protein forages by lactating dairy cows [abstract]. Journal of Dairy Science. 89(Suppl. 1):449. Interpretive Summary:
Technical Abstract: Forages are good for the environment and cow health. However, forages of sufficient quality often have elevated levels of rumen-degraded protein (RDP), much of which is converted to ammonia by ruminal microorganisms and excreted as urea. As a result, efficiency of N utilization by lactating cows fed high-forage rations can be low, leading to an increased risk of N leaving the farm through ammonia volatilization from manure or via nitrate losses in water. Despite high CP concentration in high quality grass and legume silages, protein supplementation has resulted in economical milk protein yield responses. The rumen operates as a continuous culture system and microbial growth is dependent on appropriate sources of both N and energy; this has led to suggestions that lack of synchronization of N and energy release is one reason for the low efficiency of the capture of N by ruminal microbes. However, there is little experimental evidence to support improved N utilization in response to timing energy and N release. For grass silage based diets, the incremental N from earlier harvest is better utilized than that from increased N fertilization due to improved fermentable energy supply. Feeding red clover silages has improved N utilization compared with alfalfa silages but, compared with grass silages, N utilization has been lower. Red clover has decreased proteolysis in the silo compared with both alfalfa and grass silages. This may account for the greater ruminal out-flow of non-ammonia N, mainly as feed N. However, this has not translated into improved milk protein yield in cows fed red clover silages. Certain bacteria isolated from the rumen have very high activity for producing ammonia from free amino acids. Suppressing these organisms in the rumen may aid in improving the supply of metabolizable amino acids in dairy cows fed these hay-crop silages. Strategies for improving N utilization in cows fed diets based on high quality forages, such as supplementary feeding of energy, protein and amino acids, will be addressed. Different aspects of modification of forage plants in relation to the potential to improve N utilization also will be discussed.