They also learn that it is an acceptable option for poorly drained sites with low pH and relatively poor fertility.
Unfortunately, establishing and maintaining trefoil in unmanaged pastures on less-than-ideal sites often becomes an exercise in frustration. To top it off, production of trefoil seed is challenging to commercial seed growers, which results in an undependable seed supply often considerably more expensive than other forage options.
With all that negativity, why the continued interest in birdsfoot trefoil? The answer lies in the fact that birdsfoot trefoil contains condensed tannins. Condensed tannins (CT) are a class of compound known as secondary plant compounds.
Secondary compounds are not directly involved in primary plant functions like growth and seed production. Instead, they provide an array of other benefits to the plants and potentially to our agricultural systems – benefits we are just beginning to understand.
The list of positive bioactive functions associated with CT is growing by leaps and bounds. We have known for a long time that it is the CT in birdsfoot trefoil that protects against pasture bloat.
When birdsfoot trefoil tissue is disrupted by chewing, CT binds strongly to proteins in the forage, which greatly decreases stability of the rumen foam that leads to bloat.
The protein-binding effect is also directly beneficial to animal nutrition because it reduces rumen-degradable protein (RDP) and soluble nitrogen (N) in the rumen. The bound protein bypasses the rumen but is released from its CT bond when it reaches the acidic environment in the abomasum and is thereafter available for normal digestion in the lower digestive tract.
This allows ruminant livestock to use the forage protein more efficiently, increasing N retention to support meat or milk production. The environment also benefits because less N is excreted in urine.
Protein binding by CT also benefits haylage production by reducing microbial processes that destroy protein during the fermentation process. This results in more protein retained for the animals eating the haylage and less N loss in silo effluent.
More recently, we have learned that CT also potentially affects fatty acid metabolism and methane generation in the rumen. Harnessing these effects could potentially improve fatty acid profiles of meat and milk as well as reducing greenhouse gas emissions associated with livestock production.
Researchers are investigating the ability of CT to help control gastrointestinal nematode (GIN) parasites in livestock. GIN control is a critical management issue for sheep and goat production in humid regions because the parasites have developed resistance to all available classes of chemical dewormers.
Haemonchus contortus, or barberpole worm, is a particular problem because it feeds on blood, and a large infestation can quickly kill lambs and kids.
New Zealand researchers were first to note that sheep grazing birdsfoot trefoil exhibited better tolerance of GIN, and this has since also been demonstrated in the U.S. The exact mechanism is still unknown, but once again we think CT is involved through some type of interference with the GIN life cycle.
The most recently discovered benefit of CT is its potential to alleviate toxicity resulting from consumption of tall fescue containing wild-type endophyte. Utah researchers discovered cattle ate more toxic tall fescue if they first grazed forages containing CT, such as birdsfoot trefoil or sainfoin.
This suggests that CT may bind to toxic alkaloids and neutralize their toxic effects on livestock. Several research groups are currently investigating this aspect of CT, which could have enormous implications for forage producers across the fescue belt.
Birdsfoot trefoil exhibits genetic variation for CT concentrations, so several breeding programs are currently working to develop varieties with optimal CT profiles. CT is not a trait where “a little is good, so more must be better.” It is possible to have too much CT in a forage, which may cancel out the benefits by negatively affecting fiber digestibility, palatability and dry matter intake.
Excessive CT concentrations are more likely to be troublesome in other CT-containing forages like sericea lespedeza or sainfoin than in birdsfoot trefoil. If anything, most trefoil varieties could use a little more CT.
At this time, there are relatively few birdsfoot trefoil varieties commercially available in the U.S. This is unfortunate because plant breeders have developed many varieties over the years. Seed growers usually cite poor seed production as the reason why they give up on birdsfoot trefoil. It seems obvious that trefoil seed production is another critical area that needs genetic improvement.
Birdsfoot trefoil has the reputation of being difficult to grow, but a large part of this may be our tendency to think of it only for sites where alfalfa will not succeed. While trefoil may tolerate poor conditions better than some other forage species, it will not excel on marginal sites. A good site for alfalfa is probably also a good site for birdsfoot trefoil.
Birdsfoot trefoil is widely adapted across the Midwest and eastern U.S. and is suitable for arid locations when irrigation is possible. It is not well adapted to heat.
Site preparation and control of competition during establishment is essential because birdsfoot trefoil seedlings are relatively weak and slow to get established. Seedbed preparation similar to that used for alfalfa will give best results.
Trefoil can be successfully established by frost-seeding if competition from existing plants is carefully controlled during the first few months of seedling growth. Because of its fine stems, even upright varieties of trefoil benefit from being grown with a grass companion that gives support to stems. Birdsfoot trefoil is compatible with most common cool-season grasses as long as grass-seeding rate is reduced to minimize competition.
Birdsfoot trefoil sometimes gets a bad rap for persistence, but poor persistence is usually a consequence of incorrect management or marginal sites. It cannot be managed the same way as alfalfa. Trefoil generates most new shoots from lateral buds on stems instead of from crown buds. Therefore, it is important to leave 3 inches of stubble behind when harvesting as hay or pasture.
Unlike alfalfa, trefoil does not rebuild significant root reserves of carbohydrate and protein during the growing season, instead waiting until fall. This means it needs a longer rest period after hay cutting than does alfalfa, and it should not be harvested during the fall.
Two to three harvests per year are possible depending on location. Birdsfoot trefoil can regenerate itself by reseeding. Successful long-term persistence of trefoil stands probably depends on this characteristic, so it is important to let a stand go to seed every so often.
On a pound-for-pound basis, birdsfoot trefoil exhibits better nutritive value than alfalfa, with similar total protein, less RDP and less cell wall, but it typically yields less per acre per year. Nevertheless, in comparative trials, cattle and sheep often gain more weight or produce more milk when eating birdsfoot trefoil pasture or haylage than when eating alfalfa.
The promise of CT in forage is sufficiently exciting that plant breeders have made a concerted effort to introduce a CT trait into alfalfa. Unfortunately, that process is still not commercialized, and meanwhile we already have a forage that can give us the benefits of CT – birdsfoot trefoil. FG
Michigan State University