Research aims to increase alfalfa's value in dairy diets
The amount of alfalfa used in dairy-cow diets is declining, a trend Neal Martin would like to see reversed. Martin, director of the U.S. Dairy Forage Research Center (USDFRC), Madison, WI, says USDFRC scientists and collaborators are revamping alfalfa to offer dairy producers a more efficient product.
As wheat, soybean, corn and corn silage acres have increased, the number of alfalfa acres harvested in the U.S. has declined, he says. USDA figures show that alfalfa acreage dropped from 23.7 million acres in 1998 to 21 million in 2008. Martin estimates that, between 2003 and 2007, acreage harvested as hay and haylage declined by 4%.
Less alfalfa is being used in dairy diets because of the popularity of corn silage and the relatively recent incorporation of byproducts, he says.
“The old idea of having just alfalfa and corn grain in dairy rations is gone. In California, the No. 1 dairy state, the amount of alfalfa hay in the cow diet is declining rapidly … because they're taking a lot of byproducts and making milk out of them. The cow is somewhat a consumer of waste products.”
Those byproducts, from the food, fiber and fuel industries, include canola, cottonseed, distillers grains, bakery byproducts, almond hulls and citrus pulp.
Dairies are also feeding straw as a source of fiber — another benefit that alfalfa has served in rations.
“Seeing the declining amount of alfalfa in dairy diets is a concern, because we believe perennial forage crops are good for the environment; they're good for cow health. Our mission is to develop the science to be able to enhance the utilization of perennial forages with dairy cattle.”
Alfalfa's limitations? Its protein isn't effectively utilized in the rumen, it has low fiber digestibility and it hasn't increased in yield compared to corn and other crops, Martin says.
The USDFRC, in addition to and as part of the Consortium for Alfalfa Improvement, has worked to improve alfalfa.
“The goal is two-fold,” Martin says. “We want to increase the availability of carbohydrates in plant cells by making plant fiber more digestible, and we want to reduce the amount of protein degraded during ensiling and in the rumen. Both goals would lead to producing milk with less feed — an economic benefit to the farmer, and fewer undigested nutrients coming out in the manure — a benefit to the environment.”
A recent development: an experimental transgenic alfalfa with reduced lignin that may improve fiber digestibility. Lignin in plants holds them upright, yet it also lowers digestibility. Down-regulating or lowering the activity level of enzymes that control lignin results in lower amounts of lignin. Two alfalfa experimental lines with the reduced-lignin trait showed up to 10% greater fiber digestibility when fed to cows and lambs in recent feeding trials.
Field trials showed that reduced-lignin alfalfa could be harvested eight to 10 days later than conventional alfalfa without losing quality, according to Dan Undersander, the University of Wisconsin forage specialist who conducted those trials. That could mean fewer cuttings per year, saved labor, machinery and fuel costs and possibly increased yield, he says. (For more on reduced lignin, see page 19 in our May issue and page 14 in our August issue.)
Research to reduce protein degradation is focused on two different approaches, according to Martin. One utilizes research with birdsfoot trefoil, a tannin-containing legume. Moderate levels of condensed tannins, when added to alfalfa, reduce protein degradation in the rumen.
“Another protein protection model we're working on is to take compounds that we've identified in red clover and insert them into alfalfa,” Martin says, adding that red clover silage has very little protein degradation.
Genetic engineering is being used to improve alfalfa, but won't be used to redesign other legumes and forage grasses, Martin says. Low profit margins make it hard for companies to justify the cost of research and development. Also, the traits most desired — better yield and persistence — are not easy to genetically engineer with just one gene and many graziers oppose biotechnology.
So USDFRC researchers are using conventional breeding techniques and looking at developing improved breeding technologies, including the use of molecular markers, to increase grass-breeding efficiency and reduce costs. Martin says his scientists are also looking to incorporate hybrid breeding into forages such as falcata alfalfa to increase yield.
Also encouraging for graziers is that most of the center's grass and non-alfalfa legume research is looking at these crops from a grazing basis, not from a hay harvesting basis.
“We have a target, and the target is the cow,” Martin says.