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.
Little differences appear between days in milk at first service and services per conception.
Facility Requirements Age at first calving affects facility requirements. For example, in a 100-cow herd, total replacements on hand increase from 84 to 98 head as age at calving increases from 24 to 28 months. The older calving heifers remain in the replacement program 4 months longer. The 24-month heifers leave the higher inventory and enter the milking string. The impact of the additional inventory is reflected in the cost of rearing these heifers.