Ace alfalfa harvesting
As the “foundation” of dairy cow diets, forages are fed at a greater percentage of the diet than any other single feed ingredient. Therefore, all other feeds used in the diet are planned around the quality and quantity of forages fed. During these difficult economic times, it is even more crucial to harvest high quality forages because forage quality directly impacts milk production, feed costs and ultimately farm profitability. In Minnesota, although we could use warmer weather, alfalfa stands are in general looking OK and weather permitting first cutting is projected to begin starting the end May for some locations in the state. Therefore, this months’ article will focus on key factors at harvesting that impact forage quality.
Unfortunately, for all the upcoming outdoor graduation parties, weddings and family picnics, weather is not something we can control. However, weather can have a significant impact on forage quality.
Temperature: Forages are typically of higher quality when growing conditions are cooler. Effects of increasing temperature on alfalfa development, as summarized by Mike Rankin from the University of Wisconsin Extension, include: decreased stem diameter, accelerated rate of maturity, increased lignification, decreased digestibility, decreased plant height, decreased leaf:stem ratio and increased protein content.
Rain: The potential for rainfall can be a significant challenge during alfalfa harvesting. Make sure you are fully prepared for first-cutting alfalfa so you can take advantage of a good weather window and avoid unnecessary harvesting delays. Delayed harvesting increases plant maturity and therefore decreases forage quality. Rainfall on cut alfalfa decreases forage yield and quality through leaching, respiration and leaf loss.
Winter Injury: If your alfalfa stand has suffered winter injury one of the recommendations to help stands recover is to delay first cutting. When you do this, plants are increasing in maturity so plan for lower forage quality than you may be used to obtaining. If weeds or grasses have encroached in areas where alfalfa stands are weak or thinning, potential impacts on forage quality include decreased forage palatability and increased fiber concentration.
Plant Maturity at Harvest
Cutting at late bud to first flower should result in very high quality alfalfa. Follow scissor cutting reports in your area or use a PEAQ measurement to get the quality desired for your feeding program. Refer to the U of MN forage website and sign up for the “Forage Quarterly” report for additional timely forage information. Specific information regarding the PEAQ sampling procedure and scissor cutting reports for alfalfa can be found at http://www1.umn.edu/mfgc/scissors.htm. If fields have a mixture of alfalfa and grasses, refer to information by Dr. Cherney from Cornell which can be found at http://alfalfa.50webs.com/quality.html.
Time of Day at Harvest
Because plants accumulate soluble carbohydrates during the daylight, long sunny days will increase the sugar and starch content of plants. After a sunny day, the sugar content of alfalfa will be highest in late afternoon and lowest in the morning (sugar in the plant is utilized by the plant during nighttime hours) and therefore, cutting in the late afternoon minimizes sugar loss prior to harvesting. A recent study conducted in Quebec (Brito et al., 2009) compared animal performance when late-lactation cows were fed p.m. versus a.m. cut alfalfa. Alfalfa was harvested as baleage and fed with a vitamin and mineral pre-mix for 24 days. Total nonstructural carbohydrate concentration (sugars and starches) of the baleage was 2.3 percentage units higher when the alfalfa was cut during the p.m. (12.8% vs. 10.5%). Cows fed the p.m. baleage consumed 0.9 kg/d more baleage and produced 1.5 kg/d more 4% fat corrected milk. Baleage digestibility was higher for p.m. compared to a.m. (apparent total tract digestibility) and in addition, microbial protein synthesis was enhanced when cows were fed the p.m. baleage.
Note: Cutting during the p.m. will however increase drying time. For example, in the study by Brito et al., (2009) discussed previously, alfalfa cut in the p.m. took 18 more drying hours compared to a.m. cut alfalfa. In addition, depending on weather and the amount of harvesting you have to do, starting to cut alfalfa in the afternoon is not always logistically possible.
Forage sugar content will also decrease due to plant respiration in the field during wilting. Therefore, a rapid wilting process will improve the amount of forage sugar content going into storage. One well documented method to decrease drying time is to cut alfalfa in wide swaths. This will increase the amount of surface area exposed to the sun. If forages will be fermented following wilting, maximizing sugar content at ensiling can aid in achieving a desirable fermentation process.
Length of Cut
When making haylage, getting the chop length correct at the time of chopping is crucial. It certainly can’t be changed later. A guideline is 3/8 inch theoretical length of chop (TLC) and the best way to assure you have the correct length of chop to provide the cow sufficient effective fiber is to use a Penn State Forage Particle box. Measure the alfalfa particle size a couple of times every day during harvest. The goal is to have between 15 to 20% of the chopped alfalfa weight on the top screen of the box. More than 20% on the top screen indicates the chop length is too long or possibly, the alfalfa is too wet for good ensiling.
Setting a Target for Forage Quality
For lactating dairy cow diets, haylage or hay with a RFV of about 160 and protein contents of 20 percent work very well. Haylage dry matters of 45 percent are about ideal. You should set a goal for the quality of alfalfa you want to feed. To achieve the target goal, start harvesting at least 20 RFV units higher than the goal. Cutting, wilting, harvest and storage changes will result in a minimum decrease of 20 RFV units from standing plant values.
The bottom line is harvesting high quality forages will increase milk yield, decrease feed cost and improve farm profitability. So, strive to achieve your high quality forage targets and have a safe and successful 2009 harvest!!