|Sensory Evaluation of Hay|
by Don Ball
Forage crop agronomists and animal nutritionists often bring up the topic of forage quality. In the course of discussing this important subject, the idea of taking core samples from various lots of hay and subsequently having the samples analyzed in a laboratory to assess forage quality is typically mentioned as well. Yet it is clear that many livestock producers don’t regularly test their hay, but instead simply rely on their ability to judge it by examining it. This raises a question about the value of sensory evaluation of hay.
Actually, much can be learned from a careful sensory examination of hay. First, the plant species present can be determined. Does the hay consist almost exclusively of a particular forage crop? Does the forage crop tend to be higher in quality than other forages? Does the hay contain weeds? If so, what percentage are weeds, and how much nutritional benefit do they provide to livestock? Could the weed species in the hay be toxic? The maturity of the hay, which one of the main factors determining forage quality, can be visually assessed. The number and maturity of seed heads and blooms, and the stiffness and fibrousness of the stems are indicators of plant maturity.
Leafiness is particularly important, because the higher the leaf content, the higher the forage quality. Leafiness can be affected by plant species, by stage of maturity at harvest, and (especially in legume hays) by handling that results in leaf loss.
Texture is a consideration. Softness usually results from early cutting, high leaf content, and a suitable moisture level at baling. When hay is "very soft" and pliable, it is difficult to distinguish between stems and leaves just by feeling the hay. "Soft" hay is soft to the touch, but stems can be detected easily. "Slightly harsh" hay has stems that are a little rough. "Harsh or brittle" hay is dry, stemmy, and unpleasant to the touch. "Extremely harsh" hay can injure an animal’s mouth, thus lowering intake.
Color alone is not a good indicator of forage quality, but it can be an indicator of harvest and storage conditions. A bright green color suggests that hay was cured quickly and protected during storage. Slow curing prolongs plant respiration, which reduces forage quality. Hay that is rain damaged after being partially dried will lose color due to bleaching. Mold growth on leaves and stems or exposure to sunlight will also bleach hay. Baling at moisture contents at or above 20 to 25% may cause high bale temperatures that result in tan to brown or black colors (commonly called "tobacco hay").
A pleasant odor indicates hay was cured properly. Moldy, musty odors may occur in hay stored at moisture contents above 16 to 18% (above 14% for 1-ton square bales). Animals may respond to off-odors by going off feed. Odors caused by heating (>125°F) result from hay being baled at too high a moisture content or from ensiling forage that is too dry. Interestingly, hay with a slightly caramelized odor is often quite palatable to livestock, even though the quality is reduced. If hay has an odor similar to silage, it can indicate good or bad fermentation; if it smells butyric acid (similar to rancid butter) it may lack palatability, and low animal intake is likely.
Dusty hay is usually the result of soil being thrown into the hay by rake teeth hitting the soil. The presence or absence of molds, dust, and odor are referred to as organoleptic qualities.
Visual inspection can also detect foreign matter (anything that has little or no feed value). Tools, sticks, rocks, wire, items of clothing, dead animals, and cow chips have all been found in hay and are obviously undesirable. Dead animals in hay can cause botulism, a deadly disease that can kill farm animals.
Sensory evaluation of hay can provide a great deal of valuable information. However, as valuable as sensory feedback may be, it is still not enough. The reason is that while sensory evaluations provide clues to forage quality (including some that are very strong indicators of good or bad forage quality) the most expert hay judge cannot be as accurate as a laboratory analysis. Thus, while sensory evaluation has a place, it does not preclude the need to sample and test hay.