That was true in the 1950's. But nowadays? There are more efficient ways of tilling a field than an ox-driven plough.
It would have made more sense to put that provision in an ordinary law, instead of in the Constitution. Meh!
Brazil and India has the highest number of cattle in the world, around 189 and 187 million respectively.
Yet Brazil slaughters cow and it doesn't look like their agriculture is suffering a lot from it.