DHI records show lifetime production and milk production per day of life to be highest for heifers calving at 22 to 24 months of age. Genetic Progress Genetic progress is improved with younger calving ages. Use only select sires on these replacements. If you follow a sound breeding program on your milking herd, then these replacements represent the best genetic pool for future herd replacements. Breeding replacement heifers to beef bulls or to average-quality natural service sires results in the loss of one generation of quality offspring.
Most dairymen are concerned about calving difficulties and age it freshening.
Heifers calving a less than 23 months of age have greater calving difficulties. Underconditioned and over-fat heifers would be expected to have greater difficulty at calving. The sires of the calves these heifers are carrying also affect calving age. Reproductive Performance Age and reproductive performance are related. Body size has a greater influence on sexual maturity than age.