Ahhh . . . Hybrid vigour eh ? Well it has been used for centuries and it's why we have the massive cows we do today.
Take a look at the double-muscled Belgian Blue or Charolias beef breeds, on the dairy front we have the HF's, a mix of the short stocky Freisian with the lanky high-yielding Holstein.
It's interesting to know that the BS does well in your country, when you mention about natural forage would that be a rye-grass hybrid or some other grass like Timothy or one of the fescues or even legumes like alfafa ?