by Tamara Scully
Improving the quality of alfalfa has been the focus of plant breeders, and today’s highly digestible alfalfa varieties are offering dairy farmers a lot more feed value. Conventional as well as genetically modified breeding approaches have yielded new choices for farmers. What makes a good alfalfa? What should farmers know about selecting, growing and feeding different alfalfa varieties?
Dr. Don Miller, of Alforex Seeds, addressed the challenges of breeding alfalfa for increased fiber digestibility at the recent Penn State Dairy Cattle Nutrition Workshop. “Over time, we’ve tried to modify alfalfa variety… as far as the potential yield you can get for milk production. New alfalfa varieties can increase milk production by up to two pounds per cow, per day, he said.
Breeding for feed
The first breeding efforts focused on enhancing the disease and insect resistance of alfalfa. Other quality factors, such as the number of leaves, bigger leaves and enhanced stem protein levels came next. Recently, breeding to increase fiber digestibility, the leaf/stem ratio, and transgenic traits such as “Roundup Ready” occurred. The challenge is to breed for the desired traits without changing the agronomics of growing the crop, Miller said.
Conventional plant breeding requires a lot of genetic diversity. Finding desired traits — such as the yield potential and the fiber digestibility of alfalfa — requires growing and sampling thousands of plants in a nursery setting, and selecting those that meet the requirements for the breeding program.
As the alfalfa plant matures, the quality decreases. The cell wall thickness increases, and is less able to degrade in the rumen. The leaf/stem ratio increases, too, contributing to decreased digestibility.
The leaves of the alfalfa plant have two or three times the crude protein of the stems, but the leaves — unlike the stem — don’t change in digestibility as the plant matures. In the prebud to bud stage, alfalfa plants are about 60 percent leaves, with 40 percent stem. As the plant moves to early flowering, the ratio changes to 50/50. At full maturity, the ratio is typically 40/60. Increasing the proportion of leaves to stem increases the feed value of the plant, and allows more flexibility in harvest timing without compromising as much quality.
“The goal is to make more of that bale digestible by the animal that eats it,” Miller said. “If we improve digestibility, we increase intake.”
Newer varieties of alfalfa not only have better feed quality, they also offer a wider harvest window. There’s been no lodging reported in these leafier varieties, launched in 2014. Alforex’s Hi-Gest Alfalfa, which is conventionally bred, improves the leaf-to-stem ratio by five to eight percent. The variety retains needed resistance to leaf disease and insects.
From 2015-2018, farmers were paid to send samples of these varieties back to the laboratory, helping to select “varieties that fit into a lot of different environments,” Miller said. “The variety choices that you make can make a change in the production,” of your dairy, and improve dairy profitability.
Maintaining the benefits
Planting higher quality alfalfa varieties isn’t enough. The farmer also has to manage the agronomy correctly in order to reap the benefits, Certified Crop Advisor Tom Kilcer, formerly of Cornell Cooperative Extension and now with Advanced Ag Systems LLC, said at the same Penn State conference.
With highly digestible alfalfa genetics, “we have a much bigger potential” in terms of forage nutrition. But the genetics are only a tool, and the field agronomy needs to be set up to maximize this potential, he explained. “This isn’t magic alfalfa.”
The first lesson is that regular, routine soil testing must be done. If the chemical profile of the soil is lacking in elements the alfalfa needs, reduced yields and reduced feed values result. The seed cost stays the same no matter whether it performs well or not, so managing the field to get optimal results is prudent.
“If pH is too low, it can’t respond to anything,” Kilcer said. Sulfur deficiencies are common, as sulfur is no longer available from the air — due to less pollution — but alfalfa requires sulfur. Lack of sulfur results in short, yellow plants. “You’ve got to get these things together.”
Another word of wisdom: do not cut by calendar date. Instead, time your cutting to target the NDF (neutral detergent fiber) you need.
“You can now harvest late, and at the same NDF digestibility,” he said, as management is more flexible with new alfalfa genetics.
The cut height is crucial to retaining the quality. Kilcer is adamant that no cutting lower than three inches in height occurs. If cut too low, the regrowth potential of the plant is significantly reduced, he said. Cutting too low also encourages weed growth. Cutting higher maximizes the plant’s ability to utilize sunlight, maximizing the regrowth potential.
The cut height also directly impacts ash levels. And ash level negatively impact milk production. If your ash content is 10 percent, you are losing almost two pounds of milk per cow, per day, compared to having no ash.
“They don’t milk on dirt,” Kilcer said.
Kilcer also advised that wide swath mowing is needed to retain the quality of the alfalfa. “Windrows are not drying, they’re composting. What you mow today goes in the silo today if you want to optimize what these alfalfas give you.”
When left overnight, there is no photosynthetic drying occurring, and you are losing energy in the forage. Using wide swath mowing techniques hastens drying and means that one-day alfalfa haylage is the achievable. He recommends a sickle bar mower for good results, and “80 percent of cutter bar width” or more for the swath. The goal is to get the forage dry as soon as possible, and pick it up, in order to retain quality. Conditioning is not needed with wide swath mowing, as it increases drying time and can cause the loss of alfalfa leaves.
When operating the merger, slow is the key. If operated too fast or too close to the ground, the quality of highly digestible alfalfa will be significantly decreased. Kilcer also recommends using a forage inoculant to protect against NDF loss from insects.
“You need to get that potential to the mouth of the cow,” he said.