That phrase comes from the saying "slamming the barn door after the horse has bolted". It's a saying. It means that whatever action has been taken, is too late. If you close the barn door after the horse has escaped from the barn, what was the point of closing the door? The horse has already escaped. The author of your text simply changed a few words of that saying to fit the context. I think what the author is trying to say is that there is no point of banning semen exports after the semen has already been extracted from the bulls. That's the only meaning I can think of.

Thank you, Zac. That's really helpful. A small suggestion : When you give a reply in this commentary area, questioners couldn't mark you as the best answerer. Maybe you can answer questioners in the below part, in this way, when the questioners reply you, you'll get a notification.

'Increasingly' is describing the verb 'to pay' in this instance. Another example would be something like "people are increasingly using credit cars as opposed to cash". Here, "increasingly" is describing the verb "to use". On the other hand "increasing" is used as an adjective when describing a noun, for example: "homes are increasing in price", here "increasing" is describing "homes" which is a noun. Here is a way to help distinguish between both "increasingly" and increasing": "The company is increasingly growing larger and larger because its customer base is increasing." In this sentence, "increasingly" is there to describe "growing" (verb) whilst "increasing" is there to describe their "customer base" (noun). I hope this helps.