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.
For example, heifers accelerated in growth were 1.9 months younger at first standing heat compared to those fed to grow at a slower rate. Dairy heifers grown at average or above daily rates will reach puberty before the desired breeding age. Lower conception rates have been reported for dairy heifers with over body conditioning. Rations that provide for average to moderate daily gains will result in adequate reproduction performance. 3 summarizes the Idaho DHI herds by services per conception by calving age in first lactation cows.