When balancing dairy cow rations, we don’t often think of ash, but higher than normal ash content could be costing you money. Ash is what is left after burning off the water and organic plant material. Ash can be derived from internal plant sources such as minerals and external sources such as soil. According to the Dairy National Research Council, grass and alfalfa hay typically will have 8 - 10 percent ash. Any more than 10 percent ash in a forage sample can be considered contamination from external sources, primarily soil added during hay harvesting or heavy rain splashing soil onto the leaves.
High ash levels in forage can cause significant challenges when balancing diets for lactating dairy cows. In 2011, 1,585 samples of legume haylage at Dairyland Laboratories, Inc. averaged 11.98 percent ash but ranged from 6.74 – 17.22 percent ash. If the producer with 17.22 percent ash feeds 20 pounds of this alfalfa silage that is 7.22 percent above expected ash concentrations, there is 1.44 pound /cow of foreign material going into the Total Mixed Ration (TMR).
In high producing dairy cows, ration space gets tight when trying to deliver the necessary nutrients to support production while keeping costs down. Because there isn’t enough ration space to deliver all of the nutrients in a 50-60 pound dry matter package the nutritionist must use more expensive, nutrient dense ingredients.
We don’t know what the impacts of soil in the diet are on the cow, such as whether it binds other nutrients, impacts fermentation or accumulates in the rumen. But we do know that dirt doesn’t make milk and that it does replace productive nutrients in the diet.
There are several preventative measures to avoid contaminating hay or haylage with soil during harvest. Harvesting hay at 3 to 4 inches will optimize forage quality and reduce soil inclusion, especially during dry weather. Using a windrow merger rather than a rake will have less soil disturbance, possibly resulting in 1-2 percent less ash. If a rake is used, ensure the rake is properly adjusted to keep the tines from touching the ground and reduce the amount of soil picked up during hay making. Wheel rakes tend to incorporate more ash than rotary rakes since they are ground driven instead of power driven. Also, using flat mower knives picks up less soil, particularly in dry weather, than curved knives that create suction to pick up downed hay and soil.
If there is a trail of dust behind the hay making equipment, then there is an opportunity to improve practices to reduce soil contamination in forages. If you haven’t given much thought about the ash analysis of your forages, it would be good to monitor it and adjust your field and farm practices to keep ash content in the normal range.
Source: Faith Cullens, Michigan State University Extension