How soon can I cut my alfalfa?
High-quality hay could be in short supply this year in the Midwest. The demand is great because fewer acres of alfalfa are being grown, loss of acres to winter kill, and the need to replace depleted inventories. The demand is also great because high-quality forage can replace some high-priced grain and supplements in the diet.
But do we risk more injury to an already stressed stand with an early cutting? We do, but it can vary with the stand depending on age, fertility, and disease pressure. If you experienced extensive winter kill on older stands, there was considerable stress to younger stands too. In these situations, we may need to compromise some quality in order to allow the stand to fully restore root crown reserves. We suggest cutting for minimum quality needed on the first cutting. You may consider allocating first crop to feed animals that do not require the highest-quality forage.
Increasingly, dairy producers and alfalfa growers realize the value of hay or haylage that exceeds the traditional target of 150 relative feed value (RFV). We see a wide range in all measurements of quality and many very high in CP, NDFD, RFV and RFQ. This may indicate many producers often desire a haylage that is higher than 150 RFV. This may be due to the desire for higher crude protein, but it may also reflect the ability to get greater intakes and greater milk production from such forage.
Relative forage quality (RFQ) is an index for ranking forages based on dry matter intake (DMI) and total digestible nutrients (TDN). RFQ = (DMI, % of BW) x (TDN, % of DM). While the formulae are different for both DMI and TDN between grasses and legumes, neutral detergent fiber digestibility or NDFD is part of both equations.
With the introduction of RFQ and the use of PEAQ sticks (predictive equations for alfalfa quality), we have the ability to better predict digestibility of forages. Should we change our target number? It depends on the animal to be fed. If we are feeding lactating dairy cows, I feel we should target RFQ >165. This should provide forage with an NDFD of > 50% and CP levels > 22%. This quality of forage would result in greater intakes and be able to support higher milk production due to greater digestibility of NDF. Under the traditional RFV system, I think we still want to target > 150 for alfalfa forage for lactating dairy animals. Remember, a PEAQ stick is used to predict quality in first crop alfalfa only.
What numbers are important as we look at our forage analysis? A typical forage test report may have more than 30 numbers to consider. Crude protein is the total protein in a forage sample. Protein is important to an animal for maintenance, production, and growth-and also possible growth of a developing calf. High crude protein is valuable, especially with high supplement prices, but we can place too high an emphasis on crude protein alone. Crude protein is further divided into soluble, rumen degradable, rumen undegradable, and insoluble fractions.
Neutral detergent fiber (NDF) is a measure of the cell wall contents and is composed of pectin, hemicellulose, cellulose, and lignin. These are considered structural carbohydrates. It is the NDF that gives a plant rigidity and support and provides fiber to a dairy animal. Pectin, hemicellulose, and cellulose are digestible by rumen microbes and provide energy to the ruminant but lignin is indigestible and can inhibit cellulose digestion. Other numbers associated with NDF are: eNDF or effective NDF, which is associated with cud chewing and healthy rumens; dNDF, which is the amount of dry matter that is digestible NDF; and finally, NDFD, which is the percent of NDF that is digestible. Neutral detergent fiber has long been negatively associated with intake potential of forage.
Lignin is an indigestible phenolic compound that is waterproof glue in plant fiber. Because of its nature, it inhibits cellulose digestion in NDF and thus can lower NDF digestibility and overall energy available from forage.
Neutral detergent fiber digestibility (NDFD) is the percent of NDF that is potentially digestible. This number is greatly influenced by lignin content. This number is usually determined by either 30- or 48-hour in vitro incubation or by NIR based on in vitro equations. The goal is to have NDFD > 50% or higher. Due to lower lignin content of grasses, NDFD is typically higher in grasses than alfalfa.