• Foggy/ Cloudy/ Frosty Weather adversely affect the quantity and quality of green fodder.
• Various types of anti-quality factors are present in fodder crops and there concentrations are changing according to the environmental condition.
• Nitrate toxicity enhanced under such condition.
• Foggy/ Cloudy/ Frosty Weather in India occurs during the month of December to January and in July to august, which are two lean periods for fodder availability.
• Ensiling green fodder can solve these entire problems by reducing toxicity and fodder availability during lean periods.
• Nitrate poisoning and concentrations in feeds and fodder for livestock depends on plant species and environmental conditions prior to harvest than on the amount of available nitrogen in the soil.
• Nitrite is one of the intermediate products in the breakdown of nitrate to ammonia and is the cause of nitrate poisoning.
• Nitrite in the bloodstream changes hemoglobin to methemoglobin results in brownish discoloration of the blood, is a sign of nitrate poisoning.
Causes of High Nitrates in Forage
All plants contain some nitrate, but excessively high amounts are likely to occur in forages having been grown under stress conditions such as: shading or low light intensity; detrimental weather, including drought, frost, hail, low temperatures; herbicide applications; and diseases.
Conversion of nitrates to amino acids and proteins is linked closely with photosynthesis. Light is the energy source for these activities, so shaded plants or lower leaves may be higher in nitrates than plants grown in full light. Tall forages planted at high plant populations, coupled with good soil fertility and adequate water, will create shade and may contain high nitrate concentrations. With normal growing conditions, it may be higher on cloudy days than on sunny days. Dangerously high levels can occur when wet, overcast days follow a severe drought.
2. Frost, Hail, or Disease
Conditions such as hail, light frost, or plant disease can damage plant leaf area and reduce photosynthetic activity. With less available energy, nitrate reduction is inhibited and nitrates accumulate in the plant.
Low temperatures retard photosynthesis of warm-season plants and favor nitrate accumulation. Extremely high temperatures also increase nitrate concentrations by reducing nitrate reductase enzyme activity.
Measures to avoid nitrate toxicity
1. Harvest as Silage
Ensiling tends to reduce the nitrate content of forages. Forages high in nitrate can lose from 40 to 60 percent of their nitrate content during fermentation. Fermentation of silage usually takes a minimum of three weeks. Harvest forages suitable for silage at the stage of maturity where forage quality and quantity are optimal.
2. Harvest Near Maturity
Crops normally have lower nitrate levels at maturity, so crops such as drought/frost damaged corn or sorghum silage should be harvested as near maturity as possible.
3. Harvest as Green Chop
Some forages are harvested at an immature stage and fed to cattle in the form of green chop. Green chop feeds that contain high nitrate concentrations should be fed immediately after chopping and never be allowed to heat before feeding. Such feeds are especially dangerous to feed to livestock.
For example, do not green chop in the evening and then feed the green chop the next morning. Heating in the pile of green chop causes the conversion of nitrate to nitrite, making the feed about 10 times as deadly.
Feeding high nitrate forage
Before feeding potentially troublesome plants such as sorghum and sudangrass, analyze the forage for nitrates. High nitrate forages still can be fed to animals if proper precautions are taken.
• Adapt cattle to high nitrate feeds gradually
• Dilute with other feeds – after three – four weeks the animal normally becomes adjusted to nitrates and the proportion of high nitrate forage can be increased
• Supplement grain - Grain dilutes the amount of nitrate in the total ration and provides the energy necessary for bacteria to quickly convert nitrite to ammonia.
• Molasses also can provide needed energy for nitrite reduction but may be cost prohibitive.
• Feed a balanced ration – Formulate rations to ensure adequate protein, vitamin A and other nutrients.
• Do not feed to stressed livestock
• Provide clean drinking water
About Author / Additional Info:
Senior Scientist(Agronomy) at National Dairy Research Institute, Karnal. My area of work is Forage Agronomy.