Amino Acids for Transition Cows

A considerable shift in dairy nutrition has been to move away from formulating rations for crude protein to focusing more on rumen degradable protein (RDP) and amino acids (AA), thereby trying to ensure maximal synthesis of microbial protein and more optimal usage of rumen undegradable protein (RUP) and metabolizable protein (MP). Amino acid requirements for far-off dry cows fed typical low energy diets appear to be easily met by ensuring adequate supplies of RDP and RUP. However, such is not the case for transition cows. Due to reduced DM intake and higher AA requirements during the peripartal period, it becomes more difficult to efficiently meet the apparent requirements of the most limiting AA. For example, balancing transition cow rations for high concentrations of Lys and Met in MP can have profound effects on postpartum cow performance. Responses have included increases in DM intake both before and after calving, increases in milk yield and milk protein concentrations, and a lowered incidence of ketosis postpartum. At least part of the effect of AA balancing on postpartum cow performance, in addition to enhanced protein synthesis, appears to be due to altered metabolism and reduced inflammation and oxidative stress. For example, transition cows fed high-Lys containing protein supplements and adequate amounts of supplemental Met to achieve ratios of Lys/Met in MP of 2.8/1 (NRC, 2001) have resulted in increased blood neutrophil phagocytosis (indicative of improved immune function), greater overall plasma oxygen radical absorbance capacity, and increased hepatic concentrations of glutathione and carnitine. Increased glutathione and carnitine concentrations in the liver increases antioxidant and B-oxidation capacity. Also, analysis of liver tissue collected during the peripartal period has indicated that Met supplementation affects expression of genes in the Met cycle, thereby potentially increasing supplies of methyl donors such as S-adenosylmethionine and antioxidants such as glutathione. Evidence indicates that maintaining a positive methyl donor balance is a challenge for transition cows. Combined, these observed benefits support that AA, not MP, are the required nutrients, and that AA have functions that go well beyond serving as building blocks for protein synthesis. A better understanding of more exact AA requirements of transition cows will be obtained with improved nutritional models and greater access to other rumen protected AA. Until then, it will be difficult to fully appreciate the benefits of balancing transition cow diets for AA.