Optimizing Protein-carbohydrate Utilization in the Rumen

摘要

Carbohydrate and protein sources should be matched up, so that they have relatively similar rates of rumen degradation. Cows should have a mixture of carbohydrate and protein sources in the diet that have varying rates of degradation.Crude protein fractions are categorized into rumen degradable protein (RDP) and rumen undegradable protein (RUP). RDP meets protein requirements for ruminal microbial growth and protein synthesis, and microbial protein (MP) can supply well over 50% of the requirements of a lactating cow. MP and RUP reaching the small intestine are absorbed and used to meet the protein requirements of the cow. When RDP exceeds the capacity of the rumen microbes to utilize it, ammonia will build up in the rumen. The excess ammonia is absorbed into the bloodstream, converted into urea by the liver, and excreted in the urine and milk. Excess urea nitrogen can be measured in the circulating blood as blood or plasma urea nitrogen (BUN;PUN) or in the milk as milk urea nitrogen (MUN). MUN is the most widely used measure. Ideally, MUN concentrations should be between 10 and 14 mg/dL. High MUN concentrations have been associated with decreased fertility due to low uterine pH and negative uterine environment.Carbohydrates also vary in degradability or availability in the rumen. Excess readily fermentable carbohydrates may result in an increased load of volatile fatty acids (VFA) in the rumen. The excess of carbohydrates can result from too much or the wrong type of carbohydrate being fed, concentrate being consumed in large bouts or cows sorting through feed to consume the concentrate preferentially over the forage. In many cases, subacute ruminal acidosis will occur, where the rumen pH is < 5.8 for a prolonged period of time. Dietary solutions include feeding enough physically effective fiber, and feeding a mixture of carbohydrate sources in the diet that have varying rates of degradation to match up with protein sources. Another dietary option is to feed additives (such as RuMin 8) that will help (1) match up a readily fermentable carbohydrate with excess RDP, and (2) produce more propionate from any available lactic acid due to increased production of S. Ruminantium. Propionate is a glucose precursor that is partitioned to the mammary gland for milk production. Optimizing protein-carbohydrate utilization in the rumen can be accomplished by supplying the proper proportions of RDP with available energy, thus, allowing ammonia to be captured and converted into MP by the microbes. Additionally, more energy is partitioned towards the mammary gland, instead of towards conversion of ammonia to urea.