Late lambing sheep generally spend less time in the bams and more time outside on pasture. This results in less health problems, especially healthier lungs. To lamb late and go right to grass with the ewes and lambs requires a top notch parasite and predator control program. Young lambs are especially susceptible to both of these problems. Without a sound parasite treatment program, lamb mortality can be high and growth rate and thriftiness will be low.
Predators are always a concern with any age sheep, but young lambs are an easy target for coyotes.
Fertilization, plant species choices, rest and recovery periods, etc., all require increased inputs and management. Regardless of time of lambing, for lambs to be sold as finished they need to be fed a grain-based diet for at least 30 days to meet acceptable U.S. standards for grade, yield and carcass size. So even if late lambing on grass occurs, unless one is selling lightweight lambs or feeder lambs, some grain will need to be fed to most lambs. There is no absolute best way to raise sheep. The diversity of production systems is an attractive feature of sheep.