Not sure if anyone else has put forth an idea on this but here’s my two cents.
The tale of how the farm got started, and how the first cow-girls reacted to suddenly finding themselves four breasted milk making machines.
During the second world war a team of scientists were working on a way to combat food shortages that we occurring due to the need to send supplies to the front. This team was working on improving milk production. However the teams research just as it was nearing completion was cancelled as the war ended. The team send to decommission the site outside of a small one horse town in order pocket more of the funds simply dumped the nearly complete formula into a nearby river. Which just happened to feed the towns water supply.
The young women of the town all note some odd changes over the next few weeks, horns, larger breasts, lactation, tails and additional breasts. Thankfully the indecency this causes doesn’t cause many problems as the only men in the town are old men, the rest having gone off to war. But the women have to figure out what to do before those men scheduled to come back do so.
One of them figures to make the best of it and proposed a dairy farm. The men when they do return are more than happy to go along with it, thus starts the first male week.