J.H. Cherney1, D.J.R. Cherney2, and K.M. Paddock1
1Soil & Crop Sciences and 2Dept. of Animal Science, Cornell University
Many alfalfa varieties currently on the market have claims of higher forage quality such as: fine stemmed, lower lignin, higher neutral detergent fiber digestibility (NDFD), higher relative forage quality (RFQ), high multifoliolate leaf expression, superior digestibility, higher feed intake, improved milk production, and superior forage quality. Higher quality alfalfa and grass varieties have the potential to significantly increase milk production and increase the proportion of homegrown feeds in rations. Increased fiber digestibility is the most important quality improvement.
Improvements in alfalfa forage quality
Changes in plant architecture (fine stems, multifoliolate trait, etc.) can lead to modest improvements in alfalfa forage quality. HarvXtra-type alfalfa varieties have reduced lignin content due to a genetic modification in lignin production. There are at least two varieties conventionally bred for reduced lignin. Reduced-lignin content by itself is of little benefit, unless it impacts NDFD. Reduced lignin could lead to increased lodging, although increased lodging has not been observed in low-lignin alfalfa varieties. Increased NDFD without large reductions in lignin also is a reasonable option, if possible.
Comparing alfalfa varieties in alfalfa-grass mixtures
While alfalfa can significantly impact grass CP content in mixtures, grass has little impact on any alfalfa quality traits in these mixtures. This means we can compare alfalfa varieties in mixtures and expect similar results as if they were in pure stands. Alfalfa-grass trials harvested in NY in 2017 included HarvXtra, Hi-Gest 360, LegenDairy XHD, WL 356HQ, WL 355RR, and Pioneer 55H94. Each individual trial contained 2-3 alfalfa varieties, with from 3-7 grasses, including meadow fescue, tall fescue, orchardgrass, festulolium, timothy, and reed canarygrass. All 2017 NDFD data here for alfalfa and grasses was based on weighted means over a 3 or 4-cut season (so higher yielding spring-cut forage counts more in the NDFD averages).
How does grass affect any delay in harvest?
One of the advantages for HarvXtra is the potential to delay harvest and end up with higher yields of similar quality, compared to conventional varieties under standard harvest regimes. University trials indicate that HarvXtra harvest can be delayed somewhere between 5 to 10 days and still have similar NDFD (48-hour) as a conventional variety harvested under a standard regime. Delayed harvest for HarvXtra could result in one less harvest per season, with similar or higher yields combined with less stress on the stand. But those estimates are for pure alfalfa stands, almost 90 percent of the alfalfa acreage in New York is sown with a perennial grass.
Grass in a mixture will dilute the high NDFD effect of improved alfalfa varieties. Based on NY 2017 data, pure HarvXtra harvested 5.5 days later provides similar NDFD as conventional varieties on a normal cutting schedule, but that interval shrinks as more grass is found in mixtures (Fig. 1). If a mixed stand is 30% grass, the HarvXtra advantage will be reduced to 4 days, and to less than 3 days at 50% grass.
Advantage of HarvXtra or Meadow fescue in mixtures
For this discussion, we are assuming that a one-percentage unit increase in NDFD likely results in significantly increased milk production. Our 2017 results on average showed a 5.3% increase in NDFD for HarvXtra over other alfalfa varieties. Replacing a conventional alfalfa variety with HarvXtra should result in a significant increase in mixture NDFD (one percentage unit) for a stand that is up to almost 60% grass (Fig. 2). Replacing a lower quality grass with meadow fescue, however, results in a significant increase in mixture NDFD down to as low as 15 percent grass in a mixture (Fig. 3). This is because grass NDFD is much higher than alfalfa NDFD. Our results in 2017 show that replacing a lower quality grass with meadow fescue increased grass NDFD an average of 9.7%. In a stand of 30% grass, the exact same increase in mixed forage NDFD is obtained by the addition of either HarvXtra or meadow fescue. As low as 5% of any grass in a mixture with alfalfa will significantly increase mixture NDFD (one percentage unit).
Economics of high quality alfalfa and grass
If we assume that HarvXtra seed costs about $6/lb more than other high quality alfalfa varieties, and is seeded at 14 lbs/acre, then over the average life of a stand (4 years) HarvXtra would cost about $20 more per acre due to seed costs. Meadow fescue does not cost significantly more than other grasses for seed, so there is no added seed costs for switching to meadow fescue.
An increase of one percentage unit NDFD (neutral detergent fiber digestibility) has been shown by feeding trials to increase milk production about 0.5 pound per cow per day. For high producing cows, the increase may be as high as 1 pound of milk per cow per day for every one percentage unit increase in NDFD. Based in NY 2017 trial results, the addition of HarvXtra and meadow fescue increased NDFD an average of 3.5 percentage units. Assuming a milk price of $17/cwt, a 1000 cow herd could increase annual milk income by $100,000 by planting HarvXtra/meadow fescue mixtures (Fig. 4). The added seed costs for using HarvXtra are not significant. Also, changing varieties or species planted is relatively farm-size neutral, with equal benefits per cow with small or large herds.
Planting HarvXtra alfalfa plus meadow fescue may increase milk income an average of $100/cow/year. Other varieties recently released with potentially higher NDFD have not been adequately evaluated. Any alfalfa or grass variety with significantly higher NDFD than conventional varieties is going to be worth the price of admission (higher seed costs). Switching from a lower quality grass to meadow fescue can impact forage quality of mixtures just as much as a switch from an average alfalfa to HarvXtra. The greatest challenge for alfalfa-grass mixtures is getting and keeping a reasonable amount of grass in the mixture (20-30% grass).
For alfalfa-grass producers, there is the added issue of having to pay for the roundup-ready trait in HarvXtra, without a practical way of utilizing that trait in mixtures. Roundup-Ready has been bundled with reduced-lignin, with no intention of ever separating these two GMO traits. The recent interest in production of “GMO-free milk” (produced with a very small amount of GMO-type feeds in a cow’s ration) could impact the success of GMO reduced-lignin alfalfa varieties, if the general public embraces this product.
Alfalfa-grass research was made possible by funding from the Northern New York Agricultural Development Program and the New York Farm Viability Institute.