I had a beef shorthorn bull. He got an infection end of june 2017. Took to vet. Given nuflor, banamine, la200. Repeated 3 days later. End of August got a heifer that had been with him preg checked by same vet. Called open. October 1st blood test preg checked heifer. Pregnant. We thought the bull had impregnated the heifer after his recovery. March 2018 heifer bags up and has a calf. So she was bred before his treatment not after. Took the bull to another vet. Semen tested sterile. Testicles had shrunk way down. Had to sell my registered bull to slaughter. Then I had a baby heifer get sick. Went to give her nuflor. Read the bottle. Why didnt the vet read the bottle before ruining my bull? As for your situation, I think if half your cows are open, you have a bull problem or a mineral problem. I'm betting bull. Dont cull the cows. Replace the bull.