*Extended comments are highlighted in blue.
Getting more milk per pound of feed can help offset increased feed costs. Rumensin has an FDA claim for “increased production of marketable solids corrected milk per unit of feed intake,” i.e., better feed efficiency.
Recent research indicates that higher Rumensin levels may result in more milk in fresh cows and greater feed efficiency in later-lactation animals. The higher levels generally cost less than 2¢ more per cow per day.
FDA-approved levels in complete feeds (total mixed rations) are 11 g to 22 g of Rumensin per ton of feed dry matter. I’ve always found this wording kind of confusing. For a cow eating 50 lb. of dry matter, it would result in Rumensin intakes between 275 mg and 550 mg per cow. Most dairies have been feeding on the low side of this range.
Issues with butterfat depression related to Rumensin, dietary starch and unsaturated fat levels have made dairy producers and nutritionists (myself included) reticent to try higher levels of Rumensin.
This was especially true this past year, when it seemed that butterfat was depressed in many herds due to some unknown reason (I have my theory). Now that we’re feeding corn and corn byproducts from the 2010 corn crop, it seems that butterfat is back.
Research indicates that feeding 450 mg of Rumensin per cow per day in early lactation results in significantly higher milk per cow compared to 0 mg and 300 mg. Fat test was lower on the higher dose, but, due to the increase in milk, the fat yield was higher.
Rumensin reduces the relative proportions of gram-positive bacteria in the rumen in favor of gram-negative bacteria. Gram-positive bacteria produce acetic and butyric acid. Gram-negative bacteria produce propionic acid. Propionic acid is utilized more efficiently for glucose production, hence more efficient use of feed energy. In practical terms, the higher dose of Rumensin can replace the equivalent of up to 2 lb. of corn energy in the diet.
The rumen bacteria require time to adjust to feed changes. If you do increase the Rumensin level in your diets, do it in steps. Increments of 50 mg per cow per day for two to three weeks would probably be sufficient.
If dry cows consume 300 mg to 350 mg of Rumensin, they will be well adjusted by the time they freshen. However, increasing the level to 450 mg in the fresh cows would require that you ratchet up the feeding rate faster than I have suggested. If 450 mg per cow is the target level for the herd, 400 mg is probably appropriate for a fresh cow ration.