Tuesday, April 30, 2013

Methionine as an antioxidant and why it is important during transition

It is well documented that parturition is a stressful period to cows. This can often result in peripartal disease and can lead to culling before lactation is even fully underway. Minimizing this eventuality is critical for the cow’s well being and farm profitability. Factors that compromise the cow’s immune system need to be eliminated or reduced.  Inflammation is commonly experienced during transition and it is the response to an offensive challenge. Increased oxidative stress is a significant contributor to (or consequence of) systemic inflammation.  Therefore, reducing the oxidative stress may enhance the cow’s chances of successfully navigating the transition phase of lactation.

Parturition is a time when the environmental stress is augmented. Reactive Oxygen Metabolites (ROS) can increase drastically, at least in part because of the doubling of metabolic rate in the liver.  ROS are oxygen containing molecules that are chemically reactive.  They are the result of normal metabolism of oxygen. The cells defend against ROS damage with enzymes referred to as “antioxidants”. If ROS is produced in excess to the cell’s antioxidant capacity, ROS can cause significant cellular damage. One of the key antioxidant enzymes in tissues including liver is glutathione peroxidase. This enzyme has a substrate glutathione (a tripeptide) that can be synthesized in part via Methionine. Preventing ROS accumulation and also providing substrates for antioxidant enzymes formation during the transition phase may predispose the cow to fewer health problems and a better overall lactational performance.

Lower ROS concentration was one of the effects highlighted by Mr. Johan Osorio (PhD candidate) during his presentation at the Mid-West ADSA meeting as a Dairy Scholar.  Osorio et al., conducted a trial to evaluate the impact of feeding a methionine enriched diet during the transition phase (-21 to +30 DIM).  The cows fed the methionine enriched diets responded with higher DMI and milk production.  The researchers evaluated several blood and liver tissues biomarkers indicative of the liver health, oxidative stress and inflammation.  Overall, the cows fed the methionine enriched diets tended or had significantly better indices for most of the parameters measured.

As noted above, one of the important biological functions of methionine is that methionine (and sulfur amino acids) acts as an antioxidant precursor.  Free and protein bound methionine can be considered direct antioxidants.  Figure 1 summarizes the metabolic pathway and its interactive points with antioxidant functions.

The results shown by Osorio et al., at the ADSA meeting support the hypothesis that feeding a methionine enriched diet during the transition period is beneficial to cows.  Their findings brought to light some results that merit further research.

Mr. Osorio was granted the Innovation in Dairy Research award at the ADSA Mid-West meeting for his contribution to the knowledge gained on transition cow metabolism.