The Agriculture Ministry in Japan might enforce BSE tests on the brain tissue of all dead cows born in 1996.

The ministry explained on Friday that the move is being considered in light of the fact that all four cows top have tested positive for the disease so far in Japan were born in March or April of that year. It estimates that about 26,000 cows born at the same time are still alive on Japanese farms.

So far, only partial BSE testing has been conducted, on cows showing symptoms of mad cow disease.

Meanwhile, at least thirteen cows raised with Japan’s fourth BSE-infected cow, from Ombetsu, Hokkaido, have been shipped outside of the northernmost main island.

A report conducted by the Hokkaido government found that the cattle farmer who raised the infected Holstein has shipped at least 43 other cows since March 1995.