Feeding dairy cattle in a drought

Securing enough forage during a drought can be a challenge. Forage supplies in a region can be sparse and expensive. But there are steps you can take to acquire the forage you need or stretch the current forage inventory.

It is important to remember that cattle don’t have a requirement for specific feedstuffs. They have requirements for nutrients such as protein, energy, fiber, vitamins and minerals.

You can feed and substitute many different specific feedstuffs as long as you meet the animal’s nutrient requirements. For example, high fiber by-products such as beet pulp and soyhulls can substitute for a portion of the fiber requirement and keep starch levels at correct levels.

Feedstuffs that typically may not be used for forage such as straw, cornstalks or soybeans can be successfully used if they are part of a balanced ration.

Evaluate forage needs and options

The first step when planning for uncertain feeding situations is to evaluate your forage inventory and needs. Work with your nutritionist to create a list of your operation’s forage requirements and determine an accurate forage inventory.

If possible, sort forages by quality. Older heifers, late lactation cows, and dry cows can perform well on lower-quality forage. After this, a strategy can be developed.

Estimating drought-stressed corn silage yield and quality

Estimate the potential corn silage yield before harvest to estimate your potential inventory. One very rough estimate is based on plant height. When there is very little or no grain present, each foot of plant height, excluding the tassel, equates to approximately one ton of silage per acre.

For example, a 5-foot-tall earless plant will yield 5 tons of silage per acre. If your corn successfully pollinated, you can base silage tonnage on estimated grain yield.

• For an estimated corn yield of 100 bushels or less, you will harvest about one ton of silage for every five bushels of grain.
• For 100-150 bushels per acre, every 7.5 bushels of corn will yield about one ton of silage.
• For estimated corn yields over 150 bushels per acre, silage yield will be about a ton per acre for every eight bushels of grain.

The nutrient value of drought-stressed corn silage can be different from normal corn silage. However, drought-stressed corn silage can be high quality if harvested at the correct moisture and fermented properly.

• Drought-stressed corn silage is usually higher in protein, higher in neutral detergent fiber, and lower in starch than normal corn silage.
• Even though fiber concentrations are high and starch concentrations are low, energy values of drought-stressed corn are usually 90 to 95% as high as normal corn silage because the fiber is often more digestible.
• The nutrient composition of drought-stressed corn will be more variable so it must be sampled and analyzed for nutrient composition more frequently.

Feeding strategies in a drought

Purchase hay or other forage

In drought years, hay crop forages are often high quality but limited in supply. One option is to purchase hay. Purchasing high-quality hay crop forage is a good option if milk prices are high and feed costs are reasonable. This may allow you to harvest or purchase lower quality hay to meet growing heifer and late lactation cow needs.

Purchasing corn silage from neighboring cash crop farmers can also be an excellent option. This can be advantageous for the livestock farmer and crop farmer. The University of Wisconsin has developed a spreadsheet and phone app that can help determine a fair price.

Reduce animal numbers

• Evaluate heifer and cow inventory.
• Right size your replacement heifer inventory. Having too many replacement heifers when forage is short and expensive has a huge effect on profitability.
• If cows are not covering their feed and other variable costs, consider culling them.
• If your barn is overcrowded and adequate replacement heifers are available, cull less productive cows, cows with high SCC or cows that will have long dry days.

Consider fall cover crops if it begins to rain in the fall

If weather patterns change and it rains later in the season, consider planting a small grain cover crop that can be harvested in early winter. These can be economical to grow and high quality if harvested at the correct stage of maturity.

Re-balance rations

Cattle must be fed a minimum amount of effective fiber to promote rumination and rumen health. This can be a challenge with a short forage supply.

• Reallocate forages and substitute high fiber co-products for a portion of the forage.
• Minimal amounts of straw are very effective at promoting cud chewing and keeping the rumen healthy.
• Many high fiber by-product feeds can provide dietary fiber, but lack effective fiber to promote cud chewing. But they can be used to decrease forage amounts and maintain rumen and cow health.

The prices for these by-products can also increase during a drought. Work closely with a nutritionist to make changes slowly and evaluate how cows respond to changes.

Collecting forage samples

The best way to know the quality of forage is to submit samples for testing. This can be done through a forage laboratory.

• Analyzed samples collect data for a forage at a specific point in time.
• Timely submitted samples that are reflective of what animals eat will provide the most accurate information to make decisions on an operation.

Collecting from on-farm storage

• When collecting samples from a bunker, pile, or AgBag, shave off a part of the bunker face as if preparing a TMR.
• Collect samples from the top, middle, and bottom in a 5-gallon bucket.
• On a clean countertop, thoroughly mix the forage, divide into quarters, and collect two diagonal quarters into a sample pile on the counter.
• Make sure to not forget fine particles when collecting and mixing.
• In a 6 x 6-inch sandwich bag, appropriately label and collect from the sample pile.
• Either submit samples immediately or freeze them.

Best practices for forage testing

It is good practice to work with one laboratory in order to collect comparable data from year to year. When coordinating with a chosen laboratory, strive to send samples early in the week to avoid spoilage and inconclusive results. If this can’t be achieved, store samples on-farm until that can be accomplished.

Potential anti-nutritional factors with drought-stressed forages

Nitrate toxicity

Drought stress can result in higher plant nitrate levels. Crops that are potentially higher in nitrates include sorghum, pearl millet, and sorghum-sudan grasses. Alfalfa and grasses are also capable of accumulating nitrates. Corn silage can accumulate nitrates, but levels will decrease as yields increase.

• Fermentation will reduce nitrates up to 50%.
• Cattle can somewhat adapt to nitrates. This means that the rate at which higher nitrate feeds or water are introduced to the diet will affect the animal’s risk of toxicity.
• Test any potentially high-risk forages for nitrates.
• Animals on all forage diets such as dry cows or bred heifers are more susceptible to toxicity.
• Nitrate is more of a concern if the crop is stunted and harvested shortly after significant rain. The rain will cause the plants to uptake high amounts of nitrogen into the plant.
• The lower part of a corn plant is higher in nitrates, so higher chopping height will result in lower nitrate levels.
• Total diet nitrate levels (ppm) are calculated through cumulative levels in water, grains and forages.
• Total diet nitrate levels (ppm) below 3,000 are safe, at 3,000 to 6,000 they are moderately safe if limited to 50% of the total diet DM or less, and above 9,000 are very toxic and can cause animal death.

Prussic acid (Hydrogen cyanide)

Under drought conditions, prussic acid or hydrocyanic acid can be toxic in certain situations. Plants of concern include sorghum or sorghum-sudangrass. Drought stunted plants are more likely to accumulate prussic acid.

• Freezing temperatures rupture the cells releasing cyanide. Wait to harvest or graze at least 4 days after frost to prevent prussic acid poisoning.
• Cutting and drying plants, such as when harvesting as dry hay, reduces prussic acid concentration.
• New regrowth of frosted or drought-stressed plants is extremely high in prussic acid.
• Prussic acid acts rapidly, often killing animals within minutes. Symptoms of poisoning include:
  • Increased pulse rate and respiration
  • Excessive salivation and foaming at the mouth
  • Blue coloration of the lining of the mouth
  • Difficulty breathing
  • Staggering
  • Convulsions
  • Collapse
• Death from respiratory paralysis follows shortly.

Molds and yeasts

Mold and yeast growth occurs more in stressful growing conditions such as drought or excess moisture. Molds also grow on plant material as a result of soil contamination, or injury from hail or insects.

Most molds and yeasts are not harmful to the animal, but under certain conditions, they can produce mycotoxins. Mycotoxins are potentially toxic substances produced by certain species of molds. Visible mold does not mean mycotoxins are present, and no visible mold does not mean there are no mycotoxins.

If they are present in high enough levels, mycotoxins can affect animal performance and health.

Testing for mycotoxins can be challenging and expensive. Work with your nutritionist and a lab to determine the best approach if you believe mycotoxins may be a potential problem.

• Cows that are under stress, sick, or have a compromised immune system such as transition or fresh cows are the most susceptible to mycotoxins. Younger calves are also more susceptible.
• Smut is a common mold found in drought-stressed corn. Corn smut is not a health issue for livestock.
• Aflatoxin is produced by the molds Aspergillus flavus and parasiticus (yellow or yellow-green molds). Conditions that promote the production of the mycotoxin aflatoxin are hot weather and drought stress.
  • Aflatoxin is most commonly found in corn and cottonseed.
  • The dietary limit is 20 ppb as aflatoxin can be transferred into milk where limits are set at 0.5 ppb.
• Deoxynivalenol (DON) or vomitoxin is produced by Fusarium molds (pink for reddish to white mold). This does not have a marked effect on cattle but there are some reports of digestive upset and reproductive problems and negative effects on production and feed intake. This may be a marker for other more problematic molds.
  • Maximum levels are suggested to be between 0.32 and 6 ppm.
• Zearalenone also is produced by Fusarium molds. Zearalenone has estrogenic like properties and can cause reproductive problems such as abortions, breeding problems, and enlarged mammary glands in virgin heifers.
  • Somewhat degraded in the rumen, but diet levels exceeding 500 ppb can cause reductions in milk production and reproductive problems.
• T-2 toxin is another mycotoxin produced by Fusarium molds. However, it is generally not found in silage. Dietary levels greater than 100 ppb can decrease milk production and cause diarrhea.
• Fumonisin is produced by Fusarium vertillioides and proliferatum. Fumonisin can cause liver and kidney damage at 150 ppm or more. The maximum recommended dietary level is 30 ppm.

If high levels of mycotoxins are suspected:

• Dilute contaminated feed with uncontaminated feed.
• Consider an increase in antioxidant nutrients including selenium, vitamins A and E, and trace minerals.
• Feed binders to minimize the effects of mycotoxins.

Editor’s Note: This article appears in the September issue of the I-29 Moo U newsletter and is used here with permission.