For years, Chinese companies and their contractors have been slaughtering millions of donkeys across Africa, coveting gelatin from the animals’ hides that is processed into traditional medicines, popular sweets and beauty products in China. But a growing demand for the gelatin has decimated donkey populations at such alarming rates in African countries that governments are now moving to put a brake on the mostly unregulated trade. The African Union, a body that encompasses the continent’s 55 states, adopted a continentwide ban on donkey skin exports this month in the hope…