Interest in reduced-lignin alfalfa has producers wondering, “Should I grow it?” and dairymen wondering, “Will it give me more milk? And how should I feed it?” David Weakley, director of forage nutrition research for Forage Genetics International, discussed reduced-lignin alfalfa at a World Dairy Expo 2016 seminar.
As every producer knows, there is a tradeoff between alfalfa forage yield and quality with advancing stages of maturity. We could cut 6-inch alfalfa and get really high quality, but that would result in very little tonnage. Conversely, we can wait until it matures to get the tonnage, but at full-flower the quality decreases significantly. So finding the balance or best of both worlds is the goal, and Weakley said reduced-lignin alfalfa is a tool that can help achieve that goal.
Benefits to hay growers
For the hay producer, using the current harvest schedule would likely result in harvesting premium quality with higher neutral detergent fiber digestibility (NDFd) and relative forage quality using reduced-lignin alfalfa. If a delayed harvest schedule of seven to 10 days is used to increase tonnage, digestibility is not sacrificed. A delayed harvest can also mean fewer overall cuttings, which means reduced wheel traffic, fuel, equipment wear and labor. Fewer cuttings also improve stand persistence. The other advantage for hay producers is the flexibility offered by reduced-lignin technology, which allows for adjustment to the harvest schedule for weather or other factors.
Benefits to dairymen
There are still very few peer-reviewed feeding studies available on reduced-lignin alfalfa, as the product has just become available for commercial growers. Weakley said, however, that there is a high degree of confidence in early feeding observations and prior university trials studying the impact of increased digestibility on animal performance. He cautioned that improved NDFd (and possibly milk production) is anticipated only when the grower is using his normal (or early) cutting schedule (as opposed to a delayed cutting schedule where tonnage increases).
Weakley then answered common questions from the hay producer side of the issue and the dairyman side of the issue:
Reference for questions and answers
- BCS = body condition score
- DM = dry matter
- DMI = dry matter intake
- ME = metabolizable energy
- NDF = neutral detergent fiber
- NDFd = neutral detergent fiber digestibility
- NIR = near infrared reflectance
- RFQ = relative forage quality
- RFV = relative feed value
- TDN = total digestible nutrients
Forage producers are typically honed into these forage measurements:
- Yield
- RFQ (alfalfa)
- RFV (alfalfa)
- TDN
- Milk per ton (corn silage)
Nutritionists and dairymen are typically focusing on these nutrient and quality measurements:
- NDF and NDFd
- Starch and starch digestibility
- RDS (rumen degraded starch)
- RUNDF (rumen undegraded neutral detergent fiber or rumen fill)
- DM
- Protein
Q: Does increasing NDFd increase the energy content of alfalfa?
A: Yes, but relatively little: 10 pounds alfalfa DM x 1.0 mcal ME per pound DM x 42 percent NDF x 10 percent improvement = 0.42 mcal of ME (enough for 0.8 pounds of milk assuming all the increased ME went for milk production and not maintenance needs).
Q: The energy response seems small, so why feed alfalfa of higher NDFd?
A: To reduce rumen fill and increase DM intake. The greater impact of higher alfalfa NDFd on milk production is from increasing DM intake, rather than increasing energy concentration. If you increase space, they can eat more and gain and increase in milk production from the entire diet.
Q: How much increase can we expect from increased NDFd?
A: A one-unit increase in in-vitro digestibility of NDF was associated with a 0.37-pound-per-day increase in DMI and a 0.55-pound-per-day increase in 4 percent fat-corrected milk yield per cow. Greater DMI responses are observed with early lactation, higher producing cows that are more bulk fill limited. It’s less noticeable with lower producing cows.
Q: If I feed alfalfa of a higher NDFd, will I always see an improvement in DMI?
A: No. Only when rumen fill is excessive, forage levels are greater than about 55 percent or digestibility of forages is below average.
Q: When rumen fill is not excessive, will I see a response in DMI?
A: No. When forage levels in the diet are low (less than about 45 percent) or digestibility of forages is above average, rumen fill is not limiting intake.
Q: If I see an improvement in DMI, will I always get a milk production response?
A: Not always. If cows are poor in body condition or in later lactation, the increased energy intake will be used for tissue growth and not milk production.
Q: If I substitute alfalfa of higher NDFd into the diet and rumen fill is high and body condition is good (greater than 3.5 BCS) and cows are in early lactation, should I see an improvement in DMI and milk production?
A: Very likely. For every 1-pound increase in DMI, you should expect a 2.5-pound increase in fat-corrected milk.
Q: Two and a half pounds more milk for every 1 pound of DMI increase is impressive. How much increase in DMI can I expect with feeding alfalfa of higher NDFd?
A: The higher the substitution rate and the greater the rumen fill, the greater the impact on DMI.
Q: Why would a grower ever want to grow alfalfa of higher NDFd, particularly if he doesn’t own any cows?
A: To sell hay of higher quality for a premium price.
Q: So alfalfa hay of a higher NDFd will have a greater RFV or TDN, which commands a premium price?
A: Unfortunately not. Neither of these indexes will reflect the higher NDFd.
Q: So, if RFV or TDN won’t reflect the higher NDFd, what will?
A: RFQ, based on the associated NDFd measurement from a commercial laboratory. An NIR-predicted NDFd may under-predict highly digestible alfalfa, but in vitro should be accurate.
Q: Will all commercial labs report a higher NDFd and RFQ?
A: Not always. If the commercial lab prediction equations for NDFd are poorly represented at the extreme of the population of higher NDFd alfalfa, NDFd will be under-predicted. [Weakley said the database used in some NIR calculations is not currently as robust as it could be, because not as many samples have been evaluated. Forage Genetics International is currently intentionally populating the upper end of the database to refine their NIR prediction equation for NDF and NDFd.]
Q: Is there anything we need to do to the diet to feed highly digestible reduced-lignin alfalfa?
A: Not really. Use formulations similar to that used with any high NDFd alfalfa. If rumen fill amounts are low, there is opportunity to increase forage levels in the diet, but do not fall prey to the “add wheat straw” reaction. Another advantage to the reduced-lignin alfalfa is that if dietary forage levels and rumen fill are low, producers can harvest for tonnage instead, since higher NDFd is not needed. 
References omitted but are available upon request. Click here to email an editor.
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Lynn Jaynes
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PHOTO: Reduced-lignin alfalfa has the potential to add money to your milk check – but not in every case. Photo by Lynn Jaynes.
