1. Coping With  Drought
   
2. Feeding During Drought
3. Drought and Feed Poisoning
4. Limiting Forage Intake for Dairy During Drought
   
5. Don't Overlook Water

The incidence of prussic acid, nitrate, mycotoxin and other problems may be increased when crops are grown or harvested under extreme weather conditions. These may be kept to a minimum if good judgment is used. Several general procedures may be used to minimize risk:

Introduce suspected forages or feeds gradually over a period of one to two weeks.
Don't feed suspected items to hungry animals. Make certain that other forages and concentrates are fed prior to the suspected material.
Test suspected items for nitrate or myco-toxins, if appropriate. Often materials may be used as part of the ration, depending on levels found.
Feed a well-balanced ration with proper nutrient content, proportion of forage dry matter and particle size.
Discontinue or severely restrict intake of suspected materials when possibly related problems are encountered.
Some of the more common problems:

Nitrate Poisoning. Recent research indicates that many problems previously ascribed to nitrates may have resulted from other factors. Extremely dry or cool, wet growing conditions may prevent plants from converting nitrate to true protein, so nitrate may accumulate in stressed forages, particularly whole-plant corn silage, sorghum, sundangrass and sorghum-sudan crosses. Heavy or excessive nitrogen fertilization may aggravate the problem, especially if phosphorus and potassium needs are not met. Some weeds, including pigweed and lambsquarter, may accumulate nitrate.

Nitrate levels generally decrease somewhat during ensiling, as dangerous nitrogen oxide gas is formed. However, nitrate levels may increase in hay if it undergoes heating and molding in the bale. Under normal conditions hays and haylages may contain higher levels of nitrate than corn silage.

Risk of nitrate poisoning may be reduced by the following:

• Do not harvest suspected crops for three to five days after an appreciable rain or long cloudy spell.
• Harvest as close to usual maturities as possible.
• Cut the crop somewhat higher above the ground than usual as nitrate often accumulates in stems.
• Gradually introduce suspected forage into the ration over a period of one to two weeks and don't feed it to hungry animals.
• Utilize suspected material for silage rather than green-crop.
  Test all forages and water in the ration for nitrates if one forage contains over 1.0 percent nitrate on a dry matter basis.
• Feed at least 3-5 pounds of concentrate per head per day when suspected forages are fed.

Nitrate toxicity may result when animals suddenly consume large amounts of forage con-taining 2-3 percent or more nitrate ion on a dry matter basis. Even forage with lower levels may adversely affect reproduction or become toxic if animals are nutritionally stressed or metabolically abnormal and suddenly eat a large amount of such forage. Cattle may develop blue mucous membranes from lack of oxygen in the blood. Rumen paralysis may occur. Labored or difficult breathing may be observed. Animals may go down and die rather suddenly.

Subacute or chronic nitrate poisoning may result in more of the usual reproductive problems, including abortions. Milk production and appetite generally are not affected by subacute nitrate intake. Reproductive problems generally may be prevented if feeds are gradually introduced and the nitrate level in the total ration dry matter is kept below 0.40 percent. Because of differences in rate of dry matter intake, grazed forage is about 50 percent less toxic than stored forages.

Recommended uses for forages containing various levels of nitrate are found in Table 1. A high level of nitrate or nitrite in the water may make it necessary to further reduce intakes of nitrate-containing forage. A total intake of 30-45 grams of nitrate ion per 100 pounds of bodyweight is considered acutely toxic in normal animals. Intakes of 8-22 grams per 100 lbs may be toxic when animals are in abnormal condition or are undergoing an abrupt change in ration.

Table 1. Guide to safety of forages with various
nitrate contents*

*If one forage contains over 1% nitrate, test all
forages fed and the water. Temper levels in accordance
with nitrate and nitrite content of the water.

Use of natural or supplemental non-protein nitrogen (NPN) does not aggravate a nitrate problem or increase the incidence of nitrate poisoning. Intravenous treatment of acute cases with 4 percent methylene blue in 5 percent dextrose is often effective.

To Drought and Feed Poisoning in Dairy Cattle - Part 2