Harvesting and Feeding Drought Stressed Forages
Aug 31, 2012
|Ki Fanning Ruminant Nutritionist
This year is proving to be challenging, with the drought area more wide spread and the hay and corn crop likely to be reduced. When combined with low ethanol prices, the result is reduced ethanol production, thus limited distillers grains supply.
From a cattle feeding perspective, byproduct feeds are likely to be priced higher relative to corn, and availability could be a concern. Therefore, rations changes may be necessary, and producers should look for opportunity ingredients such as buying failed corn for silage or hay, but the nitrate level may need to be considered.
Nitrate accumulation is caused by low light conditions, severe weather and/or herbicide application. Photosynthesis converts nitrates into plant proteins so a reduction in photosynthesis will allow nitrates to build up. Low lighting conditions such as cloudy days reduce photosynthesis and allow a greater level of nitrates to build up. Likewise, hail will damage and strip leaves that are the main area of photosynthesis. Cold temperatures, disease, and insects damage all reduce a plants growth and allow for a buildup of nitrates. Herbicide applications such as 2, 4-D temporarily disrupt a plant’s normal metabolic processes. Drought conditions may cause high nitrates but soil moisture must be present to allow the plant to take up nitrates.
The level of nitrates vary by plant species, stage of maturity, part of the plant, and the amount of nitrogen applied as fertilizer. Pigweed, kochia, lambsquarter, sorghum, oats, millet, and sudangrass are notorious for high nitrate levels but other plants can also accumulate nitrates to a dangerous level. A young plant is growing fast and taking up a lot of nutrients so younger plants have a greater chance of being high in nitrates. Nitrates are greatest at the lower part of the plant and least at the top. A field fertilized heavier with nitrogen fertilizer has more nitrogen available to be converted to nitrates in the plant.
To reduce nitrates harvested, raising the cutter head so that the most nitrate-dense part of the plant is left in the field. Cut hay or silage on a sunny day starting after lunch when the plant has had time to convert accumulated nitrates to proteins. Do not harvest forages the first two days after a rain because the rain water will stimulate plants and allow for greater nitrogen uptake.
Manage around nitrates by ensiling the feed if possible, test for nitrate level, dilute high nitrate feeds in the ration to limit total ration nitrates, and feed a balanced diet. The ensiling process will reduce the nitrate level by 40 to 60%. Avoid feeding green chop silages that have been allowed to heat. Heating, without ensilation, converts nitrates to nitrites which are more toxic. Be certain silages have had at least 30 or 45 days to ensile completely prior to feeding. Test the forage to determine an approximate nitrate level but remember the level is of the sample taken not the whole (i.e. there could be pockets or bales of high nitrate feeds). Dilute the feed high in nitrates so the total diet nitrate concentration is safe for the class of animal you are feeding. Feeding a balanced diet will maximize rumen function and allow for better conversion of nitrates by the rumen microorganisms. This means that urea does not complicate the problem but may help if the diet is low in protein. Likewise, the risk of nitrate poisoning is less in high-energy rations than low-energy rations. Ruminants can be acclimated to a high nitrate level by slowly increasing the total dietary nitrates, much the same way feedlot cattle are adapted to a high grain diet. Feed your lower nitrate feeds to pregnant animals and your higher ones to growing animals.
From past experience we know that ensiling failed corn can be an excellent feed. In fact if done correctly, the silage will have an energy value close to that of normal corn silage. The energy density of the forage part of a plant decreases with maturity so harvesting the failed corn as silage needs to be done at an earlier maturity than normally harvested. The whole plant moisture content should be 65%. This will maximize the fermentability and ensure a reduction in nitrates. Without the grain in the forage, it is even more important to use an inoculant and cover the silage pile.
Grazing can be an option but is higher risk because the animals do not naturally select against feeds high in nitrates. If you have to graze forages that could be higher in nitrates be sure to not overstock the pasture or strip graze. Supplement the animals on the pasture (more at the beginning to acclimate the animals). Graze a week after a killing frost, if possible, to prevent additional nitrate accumulation.
If you have more specific questions or want to design a feed budget around the available feeds you have in stock please contact one of us. We will be glad to help.
Ki Fanning is a nutritionist at Great Plains Livestock Consulting in Eagle, Neb.