In a whole-farm simulation study in Pennsylvania, feeding a partial TMR (pTMR) to grazing dairy cows increased annual net return per cow by $260 compared to a pasture-plus-concentrate system.

The study, at USDA’s Pasture Systems and Watershed Management Research Unit at Penn State University, calculated the economics of the two types of grazing systems and that of feeding a TMR in confinement. The researchers found the two TMR systems to be equally profitable.

Compared to feeding only concentrate to pastured cows, a partial TMR system provides a more uniform ration throughout the grazing season, makes dry matter intake easier to monitor and potentially increases milk production, say the researchers. There also are environmental benefits due to better utilization of nutrients, they say.

Balancing a ration for cows on pasture is the same as for confined cows. Pasture is simply an ingredient that isn’t mixed in the mixer wagon. But the pasture forages must be tested so it’s known what the pTMR must provide, and since cows will have limited time to eat it before returning to pasture, sufficient bunk space is important.

The amount of pTMR fed will depend on the cows’ requirements, pasture quality and quantity, and land availability, they add. They recommend that it contain a minimum of 6-7 lbs of forage dry matter per cow. Corn silage is an excellent choice because it adds rumen-fermentable carbohydrates and effective fiber and dilutes the protein in pasture forages.

Flexibility is key in utilizing a pTMR, say the researchers. Producers should reformulate in response to ingredient price changes and to changes in pasture quality and quantity.