A bit more
- if you buy slightly fewer sheep than you think you will need, this gives you the opportunity to keep back some of your best ewe lambs as breeding stock. The Primitives generally go on breeding well beyond the 7 years average of commercial types (I am breeding a Hebridean ewe who will be 15 when she lambs in April, but I would expect many ewes to keep lambing until 12 or so).
Primitives are slower to 'fatten' (they don't get fat, so to finish is a better expression) and are usually about 16 months when they go for slaughter - this gives the denser, tastier meat I mentioned before.
In general you will get about 175% lambing from many Primitives, depending on your grass quality, altitude and latitude, bloodlines and so on, maybe closer to 185% for Shetlands. In 15 years of breeding sheep, we have only had to pull one Soay lamb and I think 3 Hebrideans, whereas when we kept Jacobs, they just about all needed assistance. For fatter lambs but still with good meat quality you can cross breed. We have used a narrowish Texel tup with good results, but in fact the pelvis of primitive ewes is proportionally wider than that of commercial breeds, so they can deliver quite big crossbred lambs just as easily as smaller purebred lambs.
Sheep only escape if your stock fencing is not good or there are gaps around or under gates. We have double fenced our land, with hedging between the fences - this is for biosecurity but does ensure that tups don't jump out in the breeding season in search of variety.
Sheep need grass and water most of the year, with a mineral bucket in the winter months, ad lib hay in winter and some bought concentrates in the 6 weeks leading up to lambing and for early lactation - just how much depends on your chosen breed. They need to be shorn annually - no problem for someone used to cattle, to have their feet trimmed as necessary - again just how often depends on breed, whether you land is wet or has plenty of rocks - black hoof is harder than white so tends to get fewer problems.
Lambs are more susceptible to worms but older sheep tend to be resistant to a worm burden. It used to be recommended that you worm lambs sometimes as often as every 6 weeks then move them onto clean ground - this is now seen to contribute to wormer resistance so is not recommended.
Some people give an 8disease vaccination routinely, plus Blue Tongue. Only large flocks are dipped as you need a full certification to use OPs, but various pour-ons are available for smaller numbers. The danger times for fly strike are May to October, again depending on where you live and the weather in any particular year.
Some breeds will get quite daggy so a pair of dagging shears is essential to keep their back ends clean year round.