That heat and humidity cause stress for cows and reduce production is nothing new. But it is a phenomenon whose economic impact even in moderate climates is being ever-better explained by science. The economic loss from heat stress for dairy cows is estimated to be 1.2 billion dollars per year in the USA alone. To avoid heat stress or to reduce its impact there are of course many management opportunities or feeding strategies. But on the genetic and breeding side there is also potential, with the focal point being the Slick gene. A gene with dominant heritability and which is gaining attention.