Hay is basically pasture that is mowed at early maturity and allowed to sun-cure until the moisture content drops below 20% prior to baling. Growers have to do a delicate dance with the weather, cutting hay when they hope there is the greatest likelihood of the crop drying properly before it is rained on. The plantís growth stage limits the weather window considerably since hay should be cut before it reaches the mid-bloom stage (when 50% of the plants are in bloom) to capture good nutritional content.
Once the plant's seed heads have formed, the plant switches its energy into propagation and the stalk and leaves become tougher, more fibrous and less palatable. As an example, the crude protein level of bromegrass may drop from 12.6% at mid-bloom to only 5.6% when fully mature. Researchers have estimated that allowing hay plants to stand past the boot stage when seed heads first appear can decreases crude protein levels by 1/4% per day and digestible energy by nearly 1/2% per day.
Proper Moisture Is Essential
An ill-timed thunderstorm while hay is curing can reduce leaf content by up to 15%, destroy up to 34% of the nonstructural carbohydrates, eliminate 25% of the protein yield and decrease the overall yield by up to 40%.
Baling while the moisture of the hay is still over 20%, or 18% for large rectangular or round bales, increases the chance of mold growth, decreases protein utilization and makes the hay less palatable. Wet baled hay tends to generate heat both through the continued respiration of the hay, which can create an environment of 90% to 100% humidity in the bale, and the metabolic activity of microorganisms associated with the plant material. This includes heat-resistant fungi, which become active at 113 to 150 degrees F.
Once these high moisture processes are set in motion, baled hay temperatures may rise during the next 4 to 10 weeks, especially when stored in a warm area with poor air circulation. At temperatures above 175 F, heat-producing chemical reactions worsen the situation.
A subsequent rapid oxidation of reactive compounds can cause the hay temperature to rise to ignition point ó between 448 and 527 degrees F. If enough oxygen is present, spontaneous combustion may result, not only destroying your client's hay, but placing their horses and buildings at risk.
Bales that feel or smell warm should never be stored anywhere near a barn. Hay that is over 140 F should be slowly removed from the barn since even throwing or moving the bales quickly can cause it to burst into flames. While regular hay bales may vary from 40 to 100 pounds, unusually heavy bales may have too high a moisture content.
Drying, Preservative Agents
Since heating occurs to some extent in all forages with over 15% moisture, some growers use spray-on drying agents to reduce the risk of baling too wet. The chemicals in the drying agents (usually potassium carbonate) break down the waxy cuticle layer on the stem, which increases moisture loss and may reduce curing time by 50% to 70%. These agents make the leaves less brittle, which results in less leaf and nutrient loss.
Another approach is to use a hay preservative, such as propionic acid or sodium diacetate, which inhibits mold growth and can allow growers to bale hay at up to 25% moisture. The resulting hay tends to have higher yields, better color, a higher percentage of leaves and less dust or mildew than conventionally baled hay.
Growers producing large square or round bales often use these preservatives as a precaution against spoilage even when curing conditions are ideal. It's not a bad payoff for a chemical that costs only a few dollars per ton of hay.
Both hay preservatives and drying agents are safe for use on hay for horses and have no impact on palatability. Their only drawback is that some chemicals are corrosive to the haying equipment. Hay is basically pasture that is mowed at early maturity and allowed to sun-cure until the moisture content drops below 20% prior to baling. Growers have to do a delicate dance with the weather, cutting hay when they hope there is the greatest likelihood of the crop drying properly before it is rained on. The plant's growth stage limits the weather window considerably since hay should be cut before it reaches the mid-bloom stage (when 50% of the plants are in bloom) to capture good nutritional content.