Different livestock have different nutritional requirements. Dry, mature cows need 7 to 8 percent protein and 50 to 54 percent TDN in their diet. In contrast, two-year-old heifers that are nursing calves need more than 10 percent protein and 62 to 64 percent TDN to milk, rebreed, and grow properly. If you feed poor hay next winter to these nursing heifers, or even to mature cows, your animals may not rebreed, their calves will be weakened, and growth will be stunted.
What causes some prairie hay to be suitable for nursing heifers while other hay may barely satisfy a dry mature cow? Although many factors are involved, the most important factor is harvest date. Prairie hay cut early, in Nebraska in late June, might have over 10 percent protein and 65 percent TDN. But as your grass get older and develops seedheads and stems, its forage quality will decline. If you wait until August to cut, protein might drop down as low as 5 percent and TDN as low as 45 percent.
Of course, you can't harvest all your hay at the same time, so some hay will be higher quality than other hay. Store your higher quality hay separate from your average or lower quality hay. And then feed this higher quality hay to nursing heifers or other animals that have high nutrient requirements.
Remember, you can't feed high quality unless you first harvest high quality. So start cutting your prairie hay early to get better quality. You will need fewer supplements and animal performance can improve.