As far as I know nigerian dwarf goats don't exist in the uk. When these various strains of dwarf goat were imported into the uk they came under the umbrella of pygmy goats, as a consequence the genetics are combined into one breed -the pygmy goat there may be some strains of pygmy goats which are milkier and longer in body length, slightly bigger. If you are looking for a dairy goat why not look at the smaller breeds golden guernsey,pure saanen,pure toggenburg old english /english or even a pygmy x dairy I know some people have had them although size can be unpredictable if buying kids.