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Dietary starch levels: How much is not enough?

Katie Boesche for Progressive Dairy Published on 07 August 2020
Cow at the feedbunk

The fresh cow period is the time of greatest opportunity during a cow’s lactation. Starting cows off strong can result in increased peak milk, an ideal lactation curve and improved income over feed cost.

But the post-fresh period can also be a time of risk.

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Historically, the risk of subacute ruminal acidosis (SARA), displaced abomasum (DA) or other health issues has resulted in a conservative approach to the fresh cow diet, especially when it comes to starch. Because there’s no minimum requirement for starch, specifically, farmers and nutritionists often err on the low side to avoid potential consequences.

But research has shown that early lactation cows may benefit from greater levels of rumen-available starch when fed at appropriate amounts. A fresh cow diet balanced for the proper rumen-available starch levels can result in improved meal sizes, increased milk yield and fat-corrected milk, and reduced body condition loss when fed through the first 20 to 30 days of lactation.

It’s time to consider upping your fresh cow starch game to take advantage of a stronger pre-fresh ration approach.

Keeping up with management changes

When fresh cow health issues happen, we can be quick to point the blame at starch in the ration. High starch levels can carry a risk, but management often plays just as much or more of a role in fresh cow issues. Anything causing cows to go off feed, reduce intake or slug feed can result in a higher incidence of SARA or other health challenges.

The good news is: The dairy industry has made great strides in cow comfort and overall management. Housing, time budgets, bunk management and easily accessible diagnostic tools have all improved to help reduce health risks.

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And because of these improvements in management and cow comfort, the average age of herds is increasing. Many herds consist of 10% to 20% or more fourth-lactation-and-greater animals. Older cows are the highest-producing cows in the herd and require more rumen-available starch to meet lactation needs. Maintaining the same starch levels as rations formulated five to 10 years ago can short-change those older cows in the post-fresh period.

Avoiding the glucose gap

For humans, if we need energy, we can simply eat a candy bar or something high in glucose for a quick energy boost. For cows, it’s not that simple.

Let’s get scientific for a minute. Propionate, the rumen fermentation end product of rumen-available starch, is absorbed through the rumen wall and converted by the liver into glucose. Lactating cows use glucose to support milk lactose synthesis, which determines milk volume. If the gap between the energy needed and the amount of glucose available is too large, production levels can drop (see sidebar below).

Fresh cow diets typically fail to supply adequate energy in the form of glucose due to lower feed intake one to 30 days in milk (DIM). Providing supplemental rumen-available starch during the post-fresh period can help close the glucose gap and support higher levels of early lactation milk production.

You can also consider a starch supplement for rations with:

  • New crop corn silage
  • New crop high-moisture corn
  • Dry corn silage
  • Limited availability of starch ingredients
  • Poorly ground dry corn
  • Corn silage with poor kernel processing

Balance pre- and post-fresh diets

The same tendency to err on the low side when it comes to starch levels applies to the pre-fresh diet. Historically, farmers and nutritionists tend to play it safe in the close-up ration and increase starch levels after calving.

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But the most important consideration for pre-fresh starch levels is ensuring they balance with post-fresh levels. A large jump from pre-fresh to post-fresh starch inclusion in the ration could put cows at higher risk for SARA and other issues.

Keep the difference in pre-fresh and post-fresh starch levels to 10% or less. Start by determining your post-fresh starch levels and work backward to determine pre-fresh levels within this benchmark. If you increase your post-fresh starch levels, you may also need to increase pre-fresh levels to maintain the balance. Setting animals up with proper nutrition in the pre-fresh period will help them be more successful post-fresh.

Target dietary levels of rumen-available starch both pre- and post-fresh will vary by farm and diet based on the group’s intake, milk production and goals, as well as other grouping, housing and management factors.

As an industry, we continue to make great strides in both management and nutrition, yet there’s still room for improvement when it comes to starch. Keep these considerations in mind and talk with your nutritionist to determine the best starch levels for your rations.  end mark

PHOTO: Low feed intake during the fresh period can lead to energy loss and reduced body condition. Courtesy photo.

References omitted but are available upon request. Click here to email an editor.

Katie Boesche
  • Katie Boesche

  • Senior Technical Support Consultant
  • Purina Animal Nutrition
  • Email Katie Boesche

What about HOT?

The Hepatic Oxidation Theory (HOT) explains some of the mechanisms controlling feed intake. Substrates, or fuels, from rumen absorption of volatile fatty acids (VFAs) and mobilization of body reserves are metabolized by the liver to produce energy.

Depending on hepatic (liver) energy status, signals are sent from the liver to the brain either stimulating or inhibiting a cow to eat. Increased substrate metabolism stimulates satiety (the signal to stop eating), while decreased substrate metabolism stimulates a cow to eat.

Propionic acid, produced from rumen fermentation of starch, is a primary driver of the satiety signal in ruminants. The liver converts propionate to glucose, which is the cow’s principal energy source and the primary milk lactose precursor.

Fresh cows have an increased demand for glucose to support milk production; therefore it’s crucial to provide adequate starch levels in post-fresh diets to support demand. Balancing the glucose supply and the satiety effects of propionate can be a challenge, and careful attention should be given to post-fresh diets.

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