All too often, producers begin hay harvest in the middle of June. By then, the tall fescue and orchardgrass are of low quality and won't sufficiently meet the nutrient needs of a lactating cow during the winter. The more mature legumes and grasses are, the more protein and digestibility drops, says Gary Bates, University of Tennessee Agricultural Extension Service. Grass pastures should first be cut at the boot- to early-head stage and then again every four to six weeks. This ensures that you will have high-quality hay, allowing cows to produce adequate milk for their calves, which keeps both cow and calf strong and healthy.

If you wait to cut the hay, you may have more tonnage, but at the expense of nutrients, which could force you to add protein and energy supplements.
Many put off cutting hay because of wet weather. However, while the rain may prevent you from getting all of it cut, what you do get cut can feed the cows calving in the spring.