When Is the Best Time of Day to Cut Hay?
It’s the eternal debate: Does cutting alfalfa and grass later in the day actually improve hay quality? The answer is both yes and no.
By Boyce Upholt | Photos By David Bagley
If you want to know if hay is high quality, who better to tell you than the animals themselves? It turns out that in a number of studies in arid climates, cows have demonstrated a clear choice: They consistently selected the taste and smell of hay that was cut in the afternoon.
In USDA research conducted in Idaho, animals were filmed selecting between hays. “They would just sort of back away from morning-harvested hay,” explains Dan Putnam, an Extension agronomist and forage specialist at the University of California, Davis. “Our field studies have confirmed that result: Higher-quality hay generally results from afternoon harvests, which can be observed in laboratory analyses.”
A Daily Cycle
Similar results have emerged from other studies in Western states across a variety of locations. The reasons why have to do with basic plant biology.
Alfalfa and grasses, like all plants, feed themselves using photosynthesis, converting sunlight and carbon dioxide into sugars. These sugars are then broken down by plant cells into other useful materials through a process called respiration. It’s a two-step sequence that first produces and then removes the sugars—which are, in the end, what make for tasty, nutritious, high-dollar hay.
It’s also a sequence whose balance shifts throughout the day. “In the evening, when the sun goes down, respiration will continue but photosynthesis stops,” Putnam explains. Which means that at night, sugars are being consumed without being replaced. So, it’s in the late afternoon, after a full day of sunlight, that a plant’s sugar content is at its peak.
Unlike fibers, these simple carbohydrates are entirely digestible. That, of course, makes the forage more marketable. “We’ve seen differences in afternoon harvests of one or two points TDN [total digestible nutrients], or five to eight points of relative feed value,” Putnam says. “However, whether this advantage is maintained depends on what happens after swathing. It can be lost if the hay takes too long to dry and stabilize the quality.”
Mike Rankin, a former Extension agent with the University of Wisconsin and now the managing editor for Hay & Forage Grower magazine, points out that when studies like Putnam’s first indicated benefits to cutting in the afternoon, researchers attempted to repeat those findings in other locales. Rankin notes that studies from New York and Wisconsin—which have more humid environments than Western states—failed to find meaningful differences based on what time of day hay was cut.
That’s because after a plant is cut, photosynthesis stops, but respiration continues so long as the cells remain fairly intact—until, in other words, the hay is dry. (Rankin says that moisture content must drop to around 60% before respiration will cease.) So, the longer the drying process takes, the more that hay quality will decline.
In humid climates, Rankin says, hay cut later in the day often will not dry sufficiently before nightfall. “So you have to go through another night cycle, when respiration is still going on,” he explains, noting that this can cut into any sugar gains accrued throughout the day. “That’s probably what evened out the effect of cutting later in the afternoon.” In many environments, in fact, morning cutting can ensure that hay has more hours of sunlight, and therefore dries more quickly—making it the preferred time of day.
Occasionally, afternoon cutting may pay off for Eastern farmers, Rankin notes. In late summer weather, it may be possible for the grass to dry quickly. Or, if the forage is harvested as green chop, to be fed directly to animals without drydown, the carbohydrates may remain.
Weather plays an important role, Putnam agrees. Some farmers, especially out East, need to “dance around the raindrops,” he says. “Avoiding rain damage is an important management factor.” But the bottom line is clear: You want your hay to dry as quickly as possible.