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High Forage Diets? 3 Things to Consider

19 October 2020

The ambiguous title for this article is because the definition of high forage diets is vague and unique to different people.

Technically speaking, a diet that is 50% forage or greater is a high forage diet - which could be considered low to normal for the Northeast part of the US, whereas this could be considered high for the Southeast US. Feeding homegrown forages is one of the most effective ways to reduce feed costs. However, implementing a high forage diet that can support high production is complex and requires the consideration of multiple factors, writes Michael Miller, dairy nutrition consultant with Trouw Nutrition.

1. Forage Inventory: The first and most obvious factor is forage inventory. Do you have enough inventory to support high forage diets and not run out of feed? If you do have to buy forage, then the cost savings of growing your own is minimized. When evaluating high forage diets, it is beneficial to measure your inventory and measure usage, and this can be done with help from your feeder and nutritionist.

2. Forage Quality: The next factor is the forage quality, more specifically fiber, as 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 % 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 at 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 you can feed in the TMR without limiting DMI.

3. Cow’s Ability: The last factor 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. The 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. So, when harvesting forages, it is critical to have a particle size that can easily be chewed and uniform to prevent sorting.


High forage diets that allow for high production are often the optimal scenario due to lower feed cost for homegrown forages. However, remember that it takes a lot of planning and components to achieve this. First is having enough forage to feed for the year, which could take a year of planning, such as a land purchase or hybrid selection.

Forage quality is vital because as the uNDF240 increases, it can limit intake and milk production. The physical form of the diet and the cow's environment will play large roles in determining whether high forage diets will be successful on any farm. Each farm is unique and will take a team approach to achieve this goal.

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