Much of the alfalfa will go for haylage or baleage but some alfalfa mixed with orchard grass will likely be dried for hay. As alfalfa dries down the potential for dry matter loss increases. While some dry matter loss is unavoidable; there are some techniques and specialized equipment that can reduce the amount of loss.
This winter at the PA Forage and Grassland Council Conference, one of the speakers said that they traded in their hay rakes for hay mergers even for use in dry hay. His reasons were to reduce dry matter (DM) loss and increase nutrient content in baled hay. Since they farm a significant number of hay acres, their return on investment may be quicker than some other farm businesses.
Where do the savings come from? Looking at the table below, raking has a range of 1-20% dry matter loss with an average of 5% DM loss. As you would expect raking alfalfa when it is nearly dry will cause the most leaf loss. The ideal moisture to rake alfalfa is between 35 and 40%. The other thing to consider is the change in nutrient concentration of the forage. Raking will typically reduce the crude protein by a ½ a point, increase NDF by 1 point and reduce digestible dry matter by 1.2 points.
I was not able to find research reported on windrow mergers. However, their losses would be expected to similar to a windrow inverter because both types of equipment pick up the windrow and do not move it across the ground. What I highlighted in the table is the difference between the swath inversion losses and raking. Swath inversion losses of 1-3% DM loss, at an average of 1% DM loss, had no effect on nutrient content.
Of course, there are another dozen things that will affect your hay quality and dry matter losses. For more information on hay harvesting losses visit this Frequently Asked Questions page from Alberta, Agriculture and Forestry.