British origin; created in conjunction with the original term 'wanker'. Used to describe someone who masturbates stallions, even within job description of one who collects semen from a stallion.
Other sayings commonly used in the same context are; "Poke in a pig", "screwing the pooch" and "Sticking the fleece"
"Thats John, our new horse wanker. terrible thing that happened to our last."