Drought Impacts on Forage Quality
Not only has increased forage costs put financial pressures on producers, with some areas causing herd liquidations that may have implications for years to come. Drought affects different forages in different manners.
Alfalfa is relatively drought resistant because its deeper root systems allow alfalfa fields to recover from drought conditions. However, drought conditions can severely limit production. In these conditions, producers should allow alfalfa to reach 10% bloom in order to help support the plant. Drought conditions may allow for slightly greater protein content at similar stages of maturity but stage of maturity still has the greatest influence on quality. Drought conditions can reduce the NDF content and improve digestibility because the reduction in stem growth may be greater than the reduction in leaf growth.
Alfalfa grown on fields fertilized with potassium may result in greater potassium content of the resulting forage, primarily due to the lower total dry matter produced. This can have a negative effect causing increased potential for milk fever, hypocalcaemia.
Drought conditions may also allow for increased weed content of alfalfa stands. Hoary Alyssum is a toxic weed that grows well in drought conditions and is particularly toxic to horses. It is also commonly found in pastures and most animals will avoid eating it if other forages are available, but this potential is greater in severe droughts. Its consumption can cause joint issues in many species and even founder in horses.
Producers using alfalfa should also be on the lookout for Blister Beetles (genus Epicauta) which may be greater in drought affected alfalfa fields in conjunction with later plant maturity, harvesting and lowered yields. Blister beetles can cause severe irritation and blistering that can prevent animal from eating.
Similar to Alfalfa, drought conditions will reduce dry matter production in grasses. Grass nutrient content can be affected to a greater level than alfalfa. Crude protein (Nitrogen) content can be elevated in grasses during drought conditions. However, significant amounts of this increased nitrogen content may be in the form of nitrates and other non-protein compounds. Horse owners in particular should have drought affected forages tested, as the true protein can often be limiting in these forages. When tested, total nitrogen, nitrate and non-protein nitrogen can be determined.
Sorghum and Sudan grass – and to a lesser extent Johnson grass and Indiangrass – can have higher prussic acid contents. Prussic acid poisoning results in reduced oxygen transport and may affect ruminants to a greater degree than non-ruminants.
With reduced grain yield, many producers are looking at harvesting the plant rather than just the grain. Drought conditions tend to increase nitrate content, particularly in lower parts of the plant. It is recommended that the bottom 10 to 12 inches be left in the field to reduce the harvested nitrates. It is recommended that corn plants be ensiled rather than baled. Ensiling can reduce the nitrate content from 30 to 60%. Resulting feed should not be feed for 21 days after ensiling in order for fermentation to be completed.
This year’s drought conditions have not only reduced forage yields, but also affected forage quality. Testing forages for fiber, protein, and nitrates can give producers a better understanding of the true value of the forages in the diet and suggest changes to the concentrate portion of the diet to help compensate for deficiencies. For more information on our feed, forage, and silage testing services, please contact:
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t: (605) 692-7611, ext. 5
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