FDA Approves Rumensin for Dairy Cows

The U.S. Food and Drug Administration on Nov 4th, 2004 approved Rumensin® (monensin sodium) for increased milk production efficiency in dairy cows. Rumensin®, a product of Elanco Animal Health, a division of Eli Lilly and Company, Greenfield, Indiana, is already approved in feed for therapeutic and production uses in feedlot cattle, pasture cattle (beef and dairy heifers, and slaughter, stocker feeder cattle), beef cows, and calves excluding veal calves. Rumensin® is the first, approved new animal drug feed ingredient for dairy cows that increases milk-production efficiency. FDA reviewed extensive data to ensure the product met all necessary efficacy, animal health, human food safety, and environmental standards. FDA has concluded that the meat and milk derived from dairy animals fed monensin sodium are safe when the animals are fed according to the approved labeling.

So how does Rumensin actually increase milk production efficiency?

Monensin is an ionophore antibiotic that functions primarily in the rumen by inhibiting certain bacteria and allowing others to proliferate. It improves the efficiency of production by influencing energy and nitrogen metabolism through changes in rumen fermentation:

1. increased production of propionic acid, resulting in a decrease in the acetate:propionate ratio and a reduction in the amount of energy wasted as carbon dioxide and methane. These effects combined result in an increase in the metabolic energy value of feeds to the animal.
2. fluctuations in ruminal pH that often occur after large meals containing fermentable starch. This may reduce fluctuations in ruminal pH and/or incidences of subclinical ruminal acidosis.
3. reduction in feed protein breakdown thereby increasing feed protein by passing from the rumen. This may allow for greater post ruminal amino acids use for milk synthesis.
4. reduction in the incidence of bloat due to the inhibition of bacteria which produce large amounts of gas-trapping mucous. This may have implications for certain metabolic diseases such as displaced abomasum.

All these effects can result in improvements in energy capture from feeds and in protein utilization and should promote higher milk production. In addition, the effects of monensin on rumen fermentation suggest an increase in the precursors for milk lactose and protein synthesis and monensin may therefore have an important role in altering milk composition.

Effects on of Rumensin on health

Rumensin has several positive effects on cow health. The increase in ruminal propionic acid production results in reduced levels of ketone bodies in early lactation cows due to a reduction in body fat mobilization. A reduction in clinical and subclinical ketosis has been demonstrated by several researchers. Monensin also has positive effects on reducing the incidence of lactic acidosis and bloat. Monensin decreases lactic acid production leading to a more stable ruminal pH and potentially reduced risk of lactic acidosis. Monensin also reduces the incidence of bloat in animals fed high concentrate diets and in pasture-fed dairy cattle. The reduction in bloat may be attributed to a reduction in rumen fluid viscosity or to reduced methane and CO2 production. It should be noted however that the FDA approval of Rumensin does not make any claims on health benefits for lactating dairy cattle.

Effects on Milk Yield

FDA approved studies using 609 lactating multiparous dairy cattle across six trial sites were provided various level of rumensin throughout lactation and the dry period. The results are presented below:

aControl vs. Rumensin, (P<0.05)
b Control vs. Rumensin, (P<0.01)
1Milk production efficiency (MPE):
Total Solids Corrected Milk Yield, lbs
Total NEL intake, (lbs adjusted for BW change)

Key Points

When Rumensin was fed to dairy cows in the above study:

• MPE was increased within the dose range of 11 g/ton
• SCM or 3.5% FCM did not change when DMI was reduced
• DMI was not affected in early lactation, but was reduced at 15 g/ton and 22 g/ton
• Milk fat % and milk protein % were not affected at the 7 g/ton and 15 g/ton levels, but reduced at the 22 g/ton dose
• Milk fat and milk protein yields were maintained equal to controls
  

Recommendations for feeding Rumensin

• Rumensin is expected to significantly increase MPE within the dose range of 11 g/ton to 22 g/ton (DM basis).
• Begin at 11 g/ton and work with your nutritionist to determine if a higher level would be of benefit.
• Feed rumensin to all cows, during lactation and during the dry period.
• There is no withdrawal time required.
  

Gabriella Varga, Dairy and Animal Science Extension