High Forage Diets: Three Factors to Consider

Trouw Nutrition

Ruminant Solutions by Trouw Nutrition, a Nutreco company, is offering guidance inspired by recent research to help evaluate the nutritional and economic benefits of feeding a high-forage dairy diet.

Technically speaking, a diet that is 50% forage or greater is a high forage diet. This ratio could be considered low to normal in the Northeast U.S. but considered high for the Southeast. While feeding homegrown forages is one of the most effective ways to reduce feed costs, implementing a high forage diet that supports high production is complex and requires the consideration of multiple factors. Research suggests three factors are critical:

  1. Forage inventory:
    The first factor is adequate forage inventory. Is sufficient inventory available to support high forage diets and not run out of feed? If additional purchased forage is required, the cost savings of home-grown forage is minimized. Insights from a feeder and nutritionist can help measure and assess a farm’s inventory and usage to evaluate the economics involved.
  2. Fiber quality: The next factor is the forage quality, more specifically fiber. Lower quality forage limits intake and milk production. Fiber has been historically quantified by neutral detergent fiber (NDF) and has been related to intake and chewing activity. Although NDF is a good indicator of intake potential, it does not account for all the intake variation. Recently, fiber digestibility has been quantified using long-term in vitro or situ fermentations for 30, 120, or 240 hours. These time points are called undigested NDF (uNDF) and can be presented on a dry matter basis or as digestibility on a percentage of NDF basis. The NDF digestibility at 30 hours (NDFD30) is a good gauge of how fast the fiber will digest and has been related to intake and milk production. The uNDF at 240 hours (uNDF240) is an indicator of indigestible NDF, which will not be digested and has been related to rumen fill and intake. Recent work from Miner Institute has shown that, for every 1%-unit increase in uNDF240 of the total mixed ration (TMR), there is a 0.84-lb. decrease in dry matter intake (DMI). These measures are essential because they set the maximum forage that can be fed in the TMR without limiting DMI.


  1. The cow’s ability to consume: The last factor to consider is the cow’s ability to consume a high forage diet. Forages have a larger particle size compared to concentrates and can lead to longer eating times. In another project from Miner Institute, cows were fed low and high uNDF240 diets with fine- and coarse-chopped timothy hay. Cows fed the high uNDF240 diet with the coarse-chopped timothy hay spent 21 minutes longer eating per day while consuming 5.5 lbs. less of DMI than the cows fed the high uNDF240 with fine-chopped timothy hay. So, reducing the hay’s particle size allowed the cows to eat more dry matter in less time. This becomes even more important when the cow’s time budget is restricted due to extended time out of the pen for milking or increased competition at the feed bunk due to overstocking of the pen. When harvesting forages, it is critical to have a particle size that can easily be chewed and uniform to prevent sorting.

Remarking on the research, Michael Miller, Ph.D., PAS, a nutritionist with Ruminant Solutions stated, “High forage diets that allow for high production are often the optimal scenario due to lower feed costs for homegrown forages. However, a lot of planning and components are necessary to achieve success with this strategy and the three factors outlined in this research should be carefully considered.”

Dr. Miller noted that assuring adequate forage inventory may take a year of planning and involve land purchase or hybrid selection. Forage quality is vital because as the uNDF240 increases, intake and milk production can be limited. Finally, the physical form of the diet and the cow’s environment play large roles in determining whether high forage diets will be successful on a farm. Dr. Miller notes that each dairy farm is unique and demands a team approach to successfully feeding a high forage diet.

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