Jim Paulson, Extension Educator–Dairy, University of Minnesota Extension
Over the past decade, dairy producers have increased their use of corn silage as a forage source in dairy rations. This has been influenced by the high price of feed, especially corn, and corn silage's high energy content, which can substitute and reduce corn inclusion rates. Due to the high yield potential of consistent forage, producers can harvest as many tons in a week as they can struggle to put up good alfalfa all summer long.
Many farms now harvest one thousand to several thousand tons of corn silage per year. With this much corn being harvested as corn silage, producers want to know which hybrid type: BMR, conventional, dual-purpose, leafy, or some other is the best choice for their particular farm operation. There are several factors, both agronomic and animal that need to be considered.
One of the first criticisms of planting BMR corn is that there is a yield drag. The question is: A yield drag of what? Typically, BMR will have a 5 to 10% decrease in dry matter yield. However, we know from many research trials that we will get a significant increase in NDF digestibility and dry matter digestibility. If we calculate yield X digestibility and compare those differences, the advantage may go to BMR corn silage. If we applied the same logic to alfalfa, we would take just three cuttings instead of four or five. We need to shift our thinking away from dry matter yields alone and begin to think about yields of digestible nutrients per acre.
Another criticism of many silage corn varieties is that they are lower in starch content. This may be the case, approximately 10% lower when compared to other conventional corn silage varieties. However, research in the Journal of Dairy Science showed similar starch content when compared to silage specific varieties. Digestibility of the starch is similar at comparable harvest moistures and processing. Strategies to consider for increasing starch content are going to a fuller season hybrid and planting on the lower side of plant populations.
If you are trying for higher than average milk production, BMR corn silage may be beneficial. The best corn silage will not guarantee high milk production; but neither will poor corn silage. Michigan State research has shown that as NDF digestibility is improved, we will generally see an improvement in dry matter intake (DMI) and most likely in production of fat-corrected milk. It is best to position BMR corn silage where DMI may be limiting production, such as transition cows, early lactation, and peak lactation. Greater peak milk almost always translates into greater total lactation yields.
Select silage corn varieties with specific goals in mind.
We have repeatedly observed that cows fed BMR corn silage will tend to eat more. This is usually a good thing but only if the cows milk more. Why do cows eat more? The BMR corn silage may be not only slightly lower in NDF, but the NDF also digests faster. How full a cow is relates to how much NDF she eats and how fast it digests. One factor in feeding a cow is rate and extent of NDF digestibility. If NDF digests too fast, as can happen with BMR, it moves out of the rumen before it is digested as much as it can be. However, if NDF digests slowly, a cow stays filled up too long and cannot eat as much as she needs. This is what happens with poor quality forage.
New corn silage harvesters can chop longer particles and process them for greater digestibility. The combination of longer fiber length and the different processing may be very beneficial to BMR corn for silage. Because of its faster rate of NDF digestion, physically effective NDF may be a concern when feeding high levels of BMR corn silage. If we want to feed greater amounts of corn silage in order to save on overall feed cost; it is necessary to increase the particle length of BMR corn silage in order to avoid some of the problems we have seen in the past. Among these have been cows that develop acidosis due to a lack of cud chewing and natural buffering. It is extremely critical to get an accurate rate of NDF digestion and utilize nutrition models that use a rate of digestion. Forage analysis should include 24- or 30-hour NDF digestibility tests.
What about the economics? All corn seed is expensive and BMR is on the high side; that, along with needing to plant an additional 10% or more, increases seed cost. But with the high price of feed, being able to use more forage, more home-produced feed and increase production may improve overall profitability. My conclusion, if done correctly, BMR corn silage will allow us to improve profit per cow and profit per acre