Feeding cereal forages – Pat Hoffman, Vita Plus

By Pat Hoffman, Vita Plus dairy technical specialist
In some ways, it seems like an unusual concept to write about feeding lactating dairy cows grass forages, but it shouldn’t since they were born to eat grass.  Furthermore, around the world, pasture grasses, grass hay and grass silage are the predominant forages fed to dairy cows.

But here in the upper Midwest, our forages of choice since the 1940s have been alfalfa and corn silage.  While feeding more cereal grasses, such as triticale, rye or oat silage, seems new to us, it’s certainly nothing new to a dairy cow.

The uptick in popularity of cereal silages is primarily driven by agronomic and nutrient management necessity in the upper Midwest.  Over the past two decades, our dairy operations have become larger, and with that comes greater demands for forage inventories.  Likewise, nutrient management plans are now common place and cereal forages have been able to capture more nutrients from manure.  Planting winter cereal crops, such as winter triticale or winter rye, also capture extra forage yield capacity as these crops are well-adapted to grow under cool fall and spring conditions.  University research and yield monitoring have observed winter triticale or rye yields of 2 to 4 tons per acre.

A few nuances and quirks come with feeding cereal silages to lactating dairy cows.  While not intrinsically true in all rations, most of the time, we see cereal silage replace legume silage in the diet because corn silage inventories on upper Midwest dairies are relatively fixed.  Comparing the similarities and differences of cereal silage and alfalfa is a great starting place to consider diet formulation.

First, cereal forages and alfalfa need to be harvested at early stages of maturity to yield a high-quality forage.  When harvested early, at the flag leaf or early boot stage of maturity, triticale and rye silages may contain 14 to 18 percent crude protein (CP) and 42 to 48 percent neutral detergent fiber (NDF).  Silage CP is largely dictated by its nitrogen fertility status, as nitrogen and CP are complementary nutrient events.

Now the differences.  Cereal forages are much lower in calcium and can be very high in potassium because grasses are luxury consumers of soil potassium.  This means dietary calcium and potassium levels need to be double checked.  Additionally, when grass crops are grown on high-potassium soils, dietary magnesium needs to be monitored very closely.  High potassium levels in grass forages and in the cow can interfere with magnesium utilization.  Thus, we often supplement a bit more magnesium when grass forages are incorporated into the diet.

A second difference in cereal grass forages is the type of fiber.  As compared to alfalfa, cereal forages have less lignin and more hemicellulose.  As a result, cereal forages have less indigestible NDF and greater NDF digestion potential as compared to typical alfalfa silage.  That all sounds perfect, but research has shown that legume forages have a greater passage rate compared to grass forages.  Alternatively, this means legume forages have a lower rumen fill effect and grass forages may result in more rumen fill, even when diets are formulated at the same NDF concentration.  This may result in slightly lower dry matter intakes (DMI) in high-producing cows consuming diets with more grass inclusion, even when diets are formulated on an equivalent NDF basis.  Unfortunately, this little quirk may negate inferences from static laboratory measurements that suggest grass forages have greater NDF digestion potential.  Right now, we do not have laboratory measurements or metrics to define rumen fill effects of a forage.

That means we have to play a bit with diets containing more grass to find a dietary NDF level that maintains DMI, rumen health, milk components and milk yield.  Despite nuances between feeding legume or grass forage in our diets, we have observed excellent milk production potential when high-quality grasses replace a portion of legume forage in the diet.