Kan mjölkkors utnyttjande av vallprotein bli bättre? : utfodringsstrategier och konserveringsmetoder

Abstract: The purpose with this literature study was to investigate the possibilities for improvement of forage protein in dairy cows with focus on feeding strategies and conservation of forage protein. The utilization of forage protein in dairy cows is often not that efficient as it could be. The feed crude protein consists of both true proteins and non protein nitrogen. The digestion of proteins in the rumen depends on the protein degradation rate and the ability of the microbes to synthesize microbial protein. The microbes need a balance between carbohydrates that provide them with energy and proteins that are degradable in the rumen. Dairy cows that have large dietary needs for protein also require ruminal undegraded proteins, which are degradable in the small intestine. Microbial proteins and ruminal undegraded proteins are absorbed as amino acids in the small intestine. To supply the dairy cows' needs for protein by feeding with forage, the proteins in the forage has to be preserved after harvest. The protein content is affected by what crop is produced, the harvest system and the choice of conservation method. The protein breakdown, proteolysis, in forage begins after harvest and continues in the beginning of ensiling. This can be prevented by wilting, to slow down the reaction, or acid treatment for a fast pH drop. There are substances that can prevent proteolysis as well. Tannins that is present in birdsfoot trefoil and polyphenol oxidase in red clover. These prevent the protein from breakdown in silage and in rumen. The proteins become available in the small intestine, which is profitable for a ruminant. Studies with alfalfa hay and silage has shown that hay undergoes less proteolysis than silage, which means that more proteins are preserved in hay. Studies have also shown that proteins in red clover silage are more preserved than in alfalfa silage because less proteolysis occurs in red clover. When the forage contains excessive amounts of non protein nitrogen and the energy source is insufficient, the microbes can't synthesize microbial proteins and the excess of nitrogen will be excreted as urea in the urine. If the nitrogen is not fixated by forage crops it will evaporate to the atmosphere as ammoniac which eventually contributes to nitrogen over-fertilizing when the rain falls down. The loss of proteins will increase the need for protein supplementation, which can be costly for the farmer. It is therefore of environmental and economical interest to decrease the nitrogen emission by improving the efficiency of utilization of forage proteins in dairy cows.