Chuck Schwab, et. al.
Department of Animal Sciences
Cornell University, NY
“Starch makes milk” is an often heard statement from field nutritionists. This makes sense because starch (and sugar) feeding increases propionate production, propionate is the primary glucogenic volatile fatty acid, glucose is used by the mammary gland to produce lactose, and lactose is the principal determinant of milk yield. As a dense source of readily fermentable organic matter, starch is also an important energy source for rumen microbial growth and synthesis of microbial protein. Rumen microbial protein is a preferred source of absorbed AA, and both research and field experience indicate that maximizing its supply requires mixing and matching feedstuffs to achieve an optimal balance of fermentable carbohydrates (starch, sugars, pectins and digestible fiber), effective fiber, and rumen degradable protein (RDP). Fermentable carbohydrates provide the energy and RDP provides the ammonia and AA that are required for microbial growth and protein synthesis. When starch is digested in the small intestine, it’s a source of absorbed glucose. Absorbed glucose also provides benefits, including sparing the use of absorbed AA for glucose synthesis. In this case, AA are conserved for milk protein synthesis.
Less appreciated is the effect that starch can have on optimizing AA usage for milk protein production. The purpose of this paper is to review experiments that examined the effect of providing different amounts and types of starch on the AA status of lactating cows and to examine the use of two commonly used nutritional models to determine the potential impact of feeding different types of starch on optimizing AA nutrition and cow performance.