Fertility is determined by hormonal balance and body condition. The following points expand on this:

  1. Body Condition is determined by nutrition and genetics (Relative Intake / Inherent Body Condition)
  2. Body Condition (fertility) can be increased by Feeding or Breeding (or a combination of both)
  3. Nutrition (body condition) can also be increased cheaply by calving and weaning on / close to the period of green grass
  4. The components of fertility (hormones / inherent body condition) are highly heritable. Therefore, fertility is highly heritable
  5. There are super fertile individuals in most herds. They need to be identified.
  6. The most fertile heifers are identified by early mating. Those that reconceive and exhibit a Short Corrected ICP are the most fertile
  7. Bulls from the most fertile cows and those with a fast 12 month Maturity Rate are multi-sired at an early age. Those producing the most calves are the most fertile
  8. Accelerate this process of natural selection for fertility (AI)
  9. Exploit the fact that there are fertile heifers in most herds. Buy young heifers, breed them early (with appropriate bulls) and keep the small percentage that are pregnant
  10. Use common sense. Heifers that don’t breed young can be retained for herd expansion. The important thing is to IDENTIFY the most fertile for bull breeding and herd improvement.

It is all very simple. This seems to be the problem.
No need to follow conventional stud breeding and “scientific” selection protocol.