By Joe Lawrence, Cornell PRO-DAIRY
Forage quality is important, it is hard to attend a meeting or read an agricultural publication without hearing this point and while there is a risk of becoming numb to the message, this spring presents yet another reminder of how critical this can be to controlling production cost on a dairy.
In a recent article (Higher Grain Prices and Lower Starch Diets) Rick Grant revisited the results of a past study at Miner Institute comparing diets with varying forage and fiber byproduct levels, the article can be found in the March 2021 Farm Report. Dr. Grant concluded the article by stating “This study showed us that we can feed higher forage diets when the forage contains highly digestible NDF. As we enter a period of higher grain and feed prices, we need to re-focus on the fact that cows can do very well on higher forage diets if the forage quality is high. And if fibrous byproducts happen to be priced competitively, we should be prepared to take advantage of their high fiber degradability.”
While striving for forage quality should always be the goal, the current price dynamics do offer an added incentive to optimize forage quality and specifically fiber digestibility entering 2021.
Hay Crops
Key factors in hay field management remain constant. As always it really boils down to optimizing yield and quality while securing the needed quantity of forage for different groups of animals on the farm. As each season presents ample chances to make low quality hay, the emphasis should be put on securing needed inventories of lactating quality feed before shifting the focus to obtaining lower quality inventory. Dynamic Harvest Schedules discusses ways to adjust management to achieve these goals.
The next step to assuring access to the right quality forage, at the right time, for the right group of animals is planning out forage storage as discussed in Strategic Forage Storage Planning.
Alfalfa and grass, or a mixture, are still the most common sources of hay crop on dairy farms and both have the potential to offer a very highly digestible feed source but understanding their differences is important to successful management.
There remains a tendency to focus in on Crude Protein (CP) when evaluating hay quality and while CP should not be completely ignored, there are better metrics for analysis. Fiber digestibility is a key area of focus and is certainly relevant in the context of higher commodity prices.
In a recent Hoards Dairyman article Dr. Dave Combs wrote, “Good forage is the combination of the right amount of fiber at the right amount of digestibility.” This is relevant to the grass and alfalfa discussion and research from Dr. Jerry Cherney at Cornell helps explain this.
In a study comparing the first cutting growth of grass and alfalfa in New York (NY), the Neutral Detergent Fiber (NDF) level of grass was found to be approximately 20 percent higher than alfalfa. However, when the NDF digestibility (NDFd) (on a percent of NDF basis) was measured, the grass NDFd levels averaged approximately 20 percent higher than alfalfa. In other words, grass has more total NDF but it is also more digestible. If this is understood it can be accounted for in proper ration development.
What the two crops did have in common was the rate of increase in NDF and corresponding rate of decline in NDFd as the crop matured. The levels of both were relatively constant until around May 10th (Ithaca, NY) at which time NDF levels began a linear increase while NDFd began a linear decrease. Between May 10th and May 30th NDF increased by 20 to 25 percent while NDFd declined by 15 to 20 percent for both crops.
An article from the University of Wisconsin, Understanding NDF Digestibility of Forages, provides a good comparison of the NDFd potential of Alfalfa, Grass and Corn Silage. Relative to the other two, grass has the highest potential, however, it can also measure the lowest levels if mis-managed, a higher risk, higher potential reward scenario. In contrast, alfalfa has the lowest potential of the three at the high-end but does not drop as low as grass on the low-end. Carrying this idea into mixed stands, Dr. Cherney has found that as little as 5% grass in a mixture can result in increases in NDFd that are meaningful to the cow and stands with approximately 30% grass optimize yield and quality.
The Cornell study exploring the springtime changes in fiber referenced above also helps shed light on why using CP as a quality indicator can be misleading with these crops. Crude Protein was tracked in the alfalfa and grass throughout the month and CP in both crops declined at a similar rate from May 10th to May 18th, from a starting point of 23 percent CP down to approximately 18 percent. At this point the lines diverged with the alfalfa CP value flattening out at approximately 18 percent and staying at this level through the end of May. In contrast, the CP content of grass continued a linear decline at a rate of 0.45 percent per day which resulted in a final measurement of approximately 14 percent at the end of May.
If comparing CP alone, the late cut alfalfa (at 18 percent CP) would be considered superior to the late cut grass (at 14 percent CP); however, from a fiber standpoint they would both be problematic by this time. Understanding this relationship and adjusting harvest decisions accordingly can be especially impactful when trying to maximize forage utilization in the diet during times of high commodity prices.
Optimizing the harvest timing of first cutting can be managed by understand the stand composition (alfalfa vs. grass) and progress of the crop. This differs by year as spring conditions can vary significantly. More information can be found in the following article, Time To Check The Progress Of Your First Cutting. Several CCE Ag Teams around NY offer first cutting monitoring programs and send out weekly updates during the month of May, contact your local CCE Ag Team for more information.
Corn Silage
The 2020 growing season can be generalized by below average rainfall which challenged the corn crop in many areas; however, one benefit realized was the positive impact the drier weather had of corn silage fiber digestibility. When considering a number of potential influences on corn silage fiber, aside from unique traits like BMR, we know that rainfall tend to have one of the most significant impacts on digestibility. More information can be found in Corn silage forage quality: Hybrid genetics versus growing conditions.
With 2021 growing conditions still an unknown, it is difficult to know what the 2021 crop has in store for fiber digestibility or overall yield and quality performance. Although it is difficult to predict the growing season, our understanding of fiber digestibility can help us plan ahead and manage for the best outcomes when feeding the 2021 crop.
As discussed, in general higher levels of rainfall leads to lower levels of digestible fiber with perhaps the largest impact related to rainfall just before corn tasseling. With this information, by August we should have a relatively good idea as to whether fiber digestibility is going to trend higher (like 2020) or lower (like 2017) as demonstrated in the data from the NY VT Corn Silage Hybrid Evaluation Program annual overview.
This could help planning in two ways. First, it may influence harvest decisions, specifically chop height. Penn State summarized a number of chopping height studies and found that on-average NDFd increases by 2.5 percent for each six inches the cutting height is increased. In a situation where the 2021 growing season results in a high yielding crop but there are concerns of below average fiber digestibility, increasing corn silage cutting height may be a worthwhile consideration. Conversely, if 2021 is similar to 2020, with limited rainfall, securing adequate forage inventory may be of more concern. Understanding that this will likely be offset by higher overall digestibility in the crop suggest a lower harvest height could be worth considering.
Second, having some level of confidence in whether fiber digestibility will be above or below average prior to harvest will provide a glimpse into what diet adjustments may be needed when switching to the new corn silage crop.
An inherent challenge of a dry year is that while digestibility is often higher, overall yield is often lower. This creates a scenario where cows are likely to consume more of the forage, particularly if striving for a high forage diet to combat high commodity prices, while inventories may be stressed. Planning ahead and using this information may aid in decision making regarding how many acres on the farm are harvested for silage versus grain or if purchasing additional corn silage (standing in the field or post-harvest) is warranted.
Although this article has focused on high forage diets to combat higher commodity cost, this information can also help in planning for what commodities may be needed in the new diet. Regardless of price trends this opens the door to watch markets for relative deals on these inputs throughout the late summer and early fall to lock in favorable prices for the period this silage will need to be fed.
References
- Considerations in Managing Cutting Height of Corn Silage, Penn State
- Corn silage forage quality: Hybrid genetics versus growing conditions, Cornell University
- Dynamic Harvest Schedules, Cornell PRO-DAIRY
- Higher Grain Prices and Lower Starch Diets, Miner Institute Farm Report, March 2021
- NY VT Corn Silage Hybrid Evaluation Program annual overview, Cornell University
- Strategic Forage Storage Planning, Cornell PRO-DAIRY
- Time To Check The Progress Of Your First Cutting, Cornell PRO-DAIRY
- Understanding NDF Digestibility of Forages, University of Wisconsin