In our farm, we are using a HF bull. Conception rate is more than 50%.
The reason for using bull was the AI wasnt working. In about 40 inseminations, only 5 were successful.
Reasons
1. Incorrect detection of heat (Our fault)
2. Questionable skills of the AI Worker.
3. Incorrect time of insemination (AI worker has to decide)
4. AI Worker not available when cow is in full heat (AI worker dependent)
5. Straw quality as the AI workers are local people, they need to keep nitrogen filled properly, that is again a question mark.
In AI everything is out of your control, semen quality, method of insemination, etc.
Natural service ensures that semen is working quality, correct placement, cow satisfaction and you can perform as many times as you feel comfortable. You can perform 3 times from when heat is noticed at 12 hr intervals. That flexibility is difficult in AI worker model.
I would suggest you keep a bull, as well as cryocan with your own stock of semen. Then you can undergo training on insemination or call a good Vet to do the insemination to ensure better results.
Good luck.
Nikhil