agricultural agriculture animal-husbandry black-and-white bos Bos taurus bovine breed breeders calvers cattle commercial cows dairy dairy-breed dairy-cattle dairy-cows dehorned domesticated-ungulates farming fertile field fodder grass graze grazing green herd high-milk-yields Holstein-Friesian livestock longevity milk-production milkers milking-cows paddock pasture polled production quality reproductivity ruminant ruminating rural solid ungulates versatile