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.

Thursday, March 14, 2013

Is it important to balance AA in the diets fed to growing Holstein Steers?

On February 5th and 6th, the 24th Florida Ruminant Nutrition Symposium was held in Gainesville, FL. Several important topics were covered for both dairy and beef production. Presenters talked about immunity, environment, economics and nutrition. Dr. Richard Zinn challenged the audience to consider balancing the AA of the receiving diets fed to lightweight (particularly Holstein) steers for the first 52 days in the feed yard.

In his presentation, Dr. Zinn covered the basic work that lead to the current metabolizable protein requirements for steers the in the Nutrient Requirements of Beef Cattle (NRC, 2000). The metabolizable protein requirements are the sum of the requirements for maintenance plus gain. Once the amount of metabolizable protein required by the steer is known, you can estimate the metabolizable AA requirements based on the average AA composition of bovine tissue.

The author summarized data from 11 trials showing the AA profile of the chime entering the small intestine of beef cattle. The AA profile was very consistent and according to Dr. Zinn, during the latter growing and finishing phases, microbial AA will play a dominant role in satisfying the requirements. However, feedlot cattle may experience a deficiency in metabolizable AA during the early growth period. This may happen due to the relatively lower DMI compared with the genetic potential for growth.

A research trial was conducted by Carrasco et al. (2012, unpublished) to evaluate the effects of feeding increasing grams of a commercial RP-Methionine source (Smartamine® M) to a basal diet enriched with a commercial RP-Lysine source (Reashure-L™). The underlying objective of the research was to find the precise grams of methionine required to maximize the growing Holstein steers. The hypothesis was that feeding an AA balanced diet during the first phase in the feed yard to growing Holstein steers would prove beneficial.

The steers were grouped in 30 pens (5 steers/pen) and allocated five treatments. The diet for treatment one was not enriched with either commercial source of RP-AAs. Diets for treatments 2 to 5 were all enriched with the RP-Lys at 1.01% of the DM. Diets 2 to 5 were also enriched with the RP-Met at 0.032%, 0.064%, 0.096 and 1.28% of the DM. The steers received the treatment diets for the first 56 days in the feedlot, and from day 57 to day 112 all the steers received the treatment 1 diet (no RP-AA added). The calves fed the RP-AA enriched diets had slightly (but not significantly) higher ADG; however, they had a significantly higher linear and quadratic DMI efficiency (ADG/DMI). The steers fed the RP-AA diets had a highly linear increase in plasma Met; but not an increase in the plasma Lys concentration. This may have been due to a lower than expected rumen protection of the commercial RP-Lys product and may also explain the lower than expected ADGs of treatments 2 to 5.

The author stated that supplementing diets to meet the metabolizable AA requirements, particularly during the early stages in the feedlot, will enhance ADG and that several AA, namely, methionine, lysine, histidine, threonine and arginine may be co-limiting growth performance.

Friday, January 11, 2013

Research Findings from the 2012 JAM Conference - Part 3

Research has shown cows fed methionine enriched diets produce more milk with better milk composition. Methionine is an essential amino acid that also plays other important metabolic functions. Immediately after calving the cow experiences a negative energy balance due to a relative low dry matter intake versus nutrient demands for high milk production. Body reserves are mobilized leading to potential excessive fat accumulation in the liver. Methionine is essential for the synthesis of Apoprotein B and for the synthesis of Phosphatidyl Choline, both necessary for the formation of very low density lipoproteins (VLDLs) required for ensuring transport of the fat away from the liver (Durand, 1992). It has also been shown in other species that methionine metabolism also plays a key role in decreasing oxidative stress.

Results from a research trial to show the impact of feeding a methionine enriched diet on the oxidative stress and immune status of cows during transition were presented at the ADSA in July 2012 (Osorio, 2012). The underlying hypothesis was that methionine would improve liver function and reduce oxidative stress and inflammation.

Three groups of cows were fed the same basal diet from 21 days before the expected calving day until 28 days after parturition. MetaSmart® or Smartamine® M were added to the basal diet to achieve a LYS:MET ratio of 2.8:1. The cows fed either, MetaSmart® or Smartamine® M, had greater albumin concentration an indicator a good liver function. Those same cows also had lower blood concentrations of Haptoglobin, Ceruplasmin, Serum Amyloid A and Interleukin-6, indicating a reduced inflammatory response. Furthermore, those cows had a better antioxidant status indicated by a higher oxygen radical absorbance capacity and glutathione concentration.The authors concluded that the cows fed the methionine enriched diets had a lower systemic inflammatory state, an enhanced liver function and a greater antioxidant capability.

Methionine is thus a key nutrient in transition cow nutrition, not only as a building block for protein synthesis but as a key intermediate to enhance the metabolic processes. This can lead to better liver function, oxidative and inflammatory status, thus allowing the dairy cow to withstand the challenges of the transition phase of lactation.