I spent the second week of January in wintry Wisconsin as part of a series of programs focused on feeding higher forage diets. Observing the obvious enthusiasm of the attendees and hearing their questions – how to best raise high quality forages, how to increase tonnage with double or triple cropping systems, how to optimize the cow’s response to high-forage diets – I was struck by what a “teachable moment” we have right now for learning how to successfully feed more forage.
I started each presentation with the simple question: “What is a high-forage diet?” At each site the consensus seemed to be at least 70% forage. At one site a producer even pointed out that feeding high corn silage diets, though increasingly common, is not really feeding high-forage because of the grain content of the silage. His point engendered discussion about what forage mixture we can realistically expect to feed to our high producing cows. A 70% forage diet containing corn silage is a misnomer compared with a diet based on some mixture of grass and legumes. We quickly focus on fiber and fiber digestibility when discussing high-forage diets, but we must remember that over 60% of the digestible nutrients from typical corn silages come from nonfiber components of the crop.
A fundamental question as we seek to formulate ever higher forage diets is: “How much forage or forage-NDF can a dairy cow actually consume?” The traditional guideline has been about 0.9% of body weight as NDF, but we know that cows can consume much more than this amount of fiber when provided with highly digestible forages. Pastured cattle consume 1.8% of body weight (i.e. 2x the benchmarked amount) as forage NDF. With typical Northeastern U.S. diets of corn silage and haycrop silage we‘ve routinely measured total NDF intake in excess of 1.5% of bodyweight for cows producing over 100 lb/day of milk. Increasingly we read of case-study herds that are able to feed 70 or 80% forage diets and still maintain 80+ lb/day of milk. Clearly, we have only scratched the surface of how much forage even a high-producing cow can consume.
At these series of meetings producers learned about some of the best forage genetics currently available for grasses, legumes, corn hybrids, sorghums, and other forages that work well with multiple cropping systems to improve forage yield per acre. As we ponder the latest forage genetics we need to bear in mind the fundamental importance of crop genetics versus stage of maturity at harvest. In 2007 Dr. Dave Mertens at the U.S. Dairy Forage Research Center in Madison, WI summarized the published research on fiber digestion kinetics of grasses and legumes. He found that lignin content was 35% less for grasses, and NDF digestibility was 34% greater, compared with legumes.
However, when the same data base was used to evaluate immature versus mature forages, averaged over both grasses and legumes, he observed that lignin content was 59% less for forages harvested at an immature stage, and NDF digestibility was 53% greater compared with forages harvested at more mature stages of maturity. What is the take-home message? Forage quality at harvest is more important than the specific type of forage planted. This does not imply that the choice of what to plant is unimportant, but we need to sharpen our focus on harvest management so that the potential feeding value of our forages is not squandered. In the absence of high quality forage, a high-forage diet is merely a recipe for limiting feed intake and milk production. And the bulls-eye of the quality target is easy to miss: Researchers at Cornell University have found that NDF digestibility decreases by 0.5 to 1.0 unit/day for alfalfa with an even steeper decline for grass.
So as we strive for higher forage diets it helps to plant advanced crop genetics with greater potential for fiber digestibility, but we cannot ignore the importance of harvesting at the correct stage of maturity. And I didn’t even talk about the feeding environment and bunk space!
The Miner Institute Farm Report is written primarily for farmers and other agricultural professionals in the Northeastern U.S. and Eastern Canada. Most articles deal with dairy and crops topics, but also included are articles dealing with environmental issues and global agriculture as well as editorial commentary.
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