Traits that are moderately heritable include fleece weight, clean wool yield, fiber diameter, and fiber density. Another factor that relates to wool production is body weight because larger sheep have more surface area to produce wool. Thus, large sheep produce more wool than small sheep. The environment can influence wool quality in a number of ways. First is the nutrition of the sheep.
Ewes tend to be stressed during the last third of their pregnancy and while nursing lambs.
This has a direct effect on the fiber diameter that is being produced. As the nutritional level of the ewe meets her needs or is above what her needs are, the fiber diameter remains constant. As the ewe becomes stressed in the latter stages of pregnancy and after lambing, that fiber diameter may decrease which creates weak areas that are susceptible to breaking. Two ways to minimiize a decrease in wool quality are to make sure ewes are eating a ration that meet their needs and to shear ewes prior to lambing. If the fibers do have weak areas, the weakness is closer to an end of the fiber than if the ewes had long wool at lambing and weren't sheared until after weaning.