From what I can tell, these are Dormer sheep, a cross between Dorset Horn rams and German Marinos. Together the two names make Dorset-Marinos, or Dormer for short.
The Dormer was specifically bred to be a mutton breed capable of adapting to cold and rainy winters, such as what we're currently experiencing in Cape Town! (It really is very wet and very chilly today, by the way!). Apparently the reason for having lambs at this time of the year is because of the abundance of food in winter, and the lack there of in summer.