Answer: The main problem stated in this excerpt is the existence of the disease called BSE, which affects humans but also cows.
Explanation: BSE is an acronym for the disease Bovine Spongiform Encephalopathy, which is also known as the mad cow disease. BSE causes problems in the functioning of neurons and brain in general and, as the text states, it affects both humans and cows. It is classified as a neurodegenerative disease that can lead to death. Moreover, one of its symptoms is loss of coordination. For that reason, cows who are sick cannot hold their heads up.