I have several steps in culling my ewes and I'm also going to talk about my breeding goals.
First, any ewe who rejects a lamb or has poor milk production (and then undersized lambs at weaning) is culled. I also cull ewes who do not have twins by their third lambing if bred as a lamb or second lambing if bred as a yearling(except my "pet" ewes-yes I do have some!).
Second,I move any ewe who has a lower quality fleece, poor conformation or a bad tail to my crossing flock. Not all of the ewes that are cross bred are lower quality as I have several ewes who are really nice, but I already have 1-3 daughters of theirs in my pure flock. My goals with the crossing flock is to eventually cull out all of the ewes who are lower quality. My other goal is to get as big a market lamb as possible from these little Shetlands as well as a few commercial ewes (Mules and Shetland/Cheviots) to sell. I also harvest all fleeces from lambs going to market so I want good fleeces on the market lambs. (I shear them for two reasons-#1 I want that wool and #2 shorn lambs look better, supposedly grow better and get a better price.)
Now for my pure flock, I am trying to improve size slightly (my ewes are around 70-80 lbs and I would like around 80-90 lbs.) I'm also trying to improve conformation and tails. Now for fleeces, I lean more toward crimpy single coated and wavy intermediate. (I do like a few double coats as long as the outer coat is still soft-so many have hairy outer coats-I know as I have quite a few in my crossing flock) I am trying to improve density, and crimp. I love luster and don't want to lose that! I want my fleeces to be in the 4-6 in. range, but longer is better than shorter (ex. I'd rather have 7 or 8 in. than 2 or 3 in.) My fleeces usually weigh between 2 1/2 -3 1/2 lbs skirted and I would like to improve fleece production to 4-6 lbs. skirted.
Now for colors, I'm not breeding for any color in particular. I would like a good mix of colors, spots, and patterns in my flock. My personal favorite color is white-I love white wool and white sheep with black points.
Now for rams, I cull for temperament-any smashers go to market! I do prefer horns (they make good handles and look nice.) Any ram with horns endangering his life would go (thankfully I've never had one that I've used for breeding.I have had ram lambs with bad horns, but they go to market without leaving their stamp on the gene pool.) I also use polled rams for breeding(for that matter I also have a few horned ewes). Why not? They are a good way to get more genetics in my flock. Also some customers don't like horns and I would not like to see any traits lost in the Shetlands (as happened to the 4-horned rams.)
Lastly, while I want all of the above in my flock,I also want them to be 100% grass fed. I do grain at lambing time, and I grain market lambs and replacement ewe lambs. My goal is to eventually cut out all grain. (I will talk about the benefits of grass vs. grain some other time.) I also make my sheep winter out doors.They do have a wind break. And again I'll talk about the benefits out wintering out doors some other time.