Adverse weather conditions like drought present dairy producers with major challenges. The largest problem is having enough forage available to feed all animal groups. The second significant problem is forage quality. The obvious questions to ask during drought situations are 1) should hay or other forage be purchased; 2) should forage intakes be kept at the minimum level recommended; 3) should more high-fiber feeds be used?
The economics of the situation, including effects on cash flow and interest charges, should receive top priority. The palatability of the items being evaluated and their suitability for use in the feeding system should also be considered. In addition to the aforementioned items, there are other risk factors that occur during a drought that can have a substantial impact on animal performance. Nitrates, prussic acid and other poisons can jeopardize both production and health of animals. Poisonous plants and weeds can be an issue and should not be overlooked.
Drought-stricken corn can make nutritious silage. Absence of ears does not imply that corn silage lacks fermentable energy. Forage portions should contain reasonably high levels of soluble sugars. As corn approaches maturity, the energy level and dry matter yield increase. It is recommended to allow corn to develop as fully as possible, even if ears and grain are lacking. There are wide variations in the nutritive content of drought-stressed corn silage. It may have an energy value 85 to 100 percent of normal corn silage, or it may be quite different. Very young corn prior to tasseling may contain as much as 14 to 16 percent crude protein. A standard forage analysis is highly recommended, along with testing for levels of nitrates.
If it becomes necessary to harvest very short immature corn, it is not prudent to add a non-protein nitrogen source like ammonia or urea at the time of ensiling. Preferably, the dry matter content of droughty silage should be in the range of 30 to 40 percent to make satisfactory silage. If the corn did not set ears and is green, or if the ears are all brown, the moisture content may be too high, but hot, dry weather can cause rapid moisture drops—careful observations of moisture changes are needed to determine the best time to harvest.
Immature plants that are killed will likely contain too much moisture for immediate ensiling. These plants will dry slowly and dry matter losses will increase as the dead plants drop their leaves. The best option is to leave the crop in the field until it reaches the appropriate dry matter level, unless losses appear too high or harvesting losses will increase dramatically.
Drought or immature soybean plants can be used as a forage crop. Plants should be allowed to mature as much as possible before harvesting. Some pod or bean development enhances feeding value of plants harvested either as hay or silage. Soybean forage is high in calcium and should be avoided as the major forage source for dry cows.
If the plants are going to be ensiled, it is recommended to do so before plant moisture drops below 60 to 65 percent. If possible, mix soybeans with other forages, preferably during ensiling to enhance palatability. If plants are high in moisture and lack pod or bean development, it is suggested to add 100 to 200 pounds of a ground grain per ton when direct-cutting rather than wilting to 60 to 65 percent moisture. The stems of soybean plants are not very palatable, and animals will sort them out if given the opportunity. Chopping soybean hay and feeding if in a total mixed ration will help prevent sorting.
If soybean forage contains substantial amounts of developed beans, you may need to reduce the amount of other fats and oils in the ration for lactating cows based on the analyzed fat content of the soybeans. It may be difficult to dry down pods for hay if beans are too well-developed. As with any forage, soybeans should be analyzed for their nutrient content. It is also advisable to check the label of any herbicide used for possible restrictions on feeding soybean forage to livestock.
Drought conditions may increase nitrate levels in forages to the point of possible toxicity. Drought-stricken fields of corn, sorghum and Sudan grass are most apt to contain harmful levels of nitrate, particularly those that have been heavily fertilized with manure or nitrogen. Numerous weeds such as pigweed and lambsquarter are nitrate accumulators. Any forage that is suspected of containing high levels of nitrates should not be fed as green chop.
Although nitrate levels in drought-stricken corn may be high, ensiling usually reduces more than half the nitrates. For this reason, nitrate toxicity rarely occurs when feeding ensiled drought corn. However, if drought damage was extreme and high levels of nitrogen were applied to the soil, a nitrate test on the silage should be conducted. Rate of nitrate intake is the most critical factor influencing possible toxicity. This is affected by rate of forage dry matter intake in a given period of time and its nitrate content. Forages containing under 1,000 parts per million nitrate-nitrogen (NO3-N) on a dry matter basis may be fed free-choice or with no restriction on meal size. That's provided the total level of NO3-N in the total ration, including water, is kept at a safe or low-risk level.