Back of the envelope math: cows live for about 20 years, but dairy cows are killed after about 4 years when their milk production slows. Assuming they are impregnated 4 times, that's (5 cows * 20 years per cow) / (4 years) = 25 times as costly. And this 25 times as costly milk has to compete with the 1 times as costly milk in a market that's already so competative that milk is sold below cost with government subsidies. It's impossible for practical purposes.