Hay, Haylage and Silage: What’s the Difference?

based on the cost per unit of dry matter the hay is better value. The most important tool for good foragebuying decisions is a forage analysis completed in a recognized laboratory. At the very least a lab analysis will tell you how much water you are buying. It isnt possible to accurately assess the value of the feed for your horse until you have proof of the nutritional analysis of it.
Nutritional characteristics
The nutritional characteristics of ensiled forage are similar to those of hay with some exceptions. Ensiled forage is preserved through the fermentation of the natural sugars in the grass to fermentation acids and so water soluble carbohydrates WSC can be lower in ensiled forages than in hay coming off the same field.
There is research in both ruminants and horses suggesting that ensiled feed can have a small increase in digestibility but the significance of this is largely determined by the nutritional content of the fresh cut grass that was ensiled. Protein quality can suffer in an ensiled forage. Growing horses and performance horses could be negatively impacted by this and so only the highest quality forage should be provided for them. 
The dry long stem grass found in hay encourages more chewing compared to wetter forages. Chewing forages encourages grinding of the feed before it reaches the stomach. Wellchewed forage has improved nutrient digestibility. Chewing also encourages saliva production an important aspect of the buffering capacity of the equine foregut.
Horses that are fed wetter forages freechoice can have amazingly high intakes. Wetter forages can be easier to eat and increases in total feed intake can be an outcome of feeding ensiled forages. If you have an overweight eating machine at home be cautious about leaving him alone with a round bale offered freechoice.