Evaluation of Milk Production and Energy Partitioning in Primiparous Braford Heifers Calving at Two- vs. Three-Years of Age

Twelve Braford cows and their calves were selected from 3 age groups (n = 4 pairs/age group), consisting of 2- and 3-yr-old primiparous and mature multiparous cows. Each pair was allocated to an individual pen in a completely randomized design. All animals were fed a daily diet of 45% concentrate and 55% forage. Body condition score, BW, and milk production data were collected from all cows on d 0, 42, and 84 after the initiation of the study. Backfat thickness was measured on d 0 and 84 using ultrasound. Mature cows lost more BW (P < 0.01) than the other groups (−0.42, 0.04, and 0.17 kg/d for mature, 2-, and 3-yr-old cows, respectively; SEM = 0.08). Two-yr-old cows had a greater (P < 0.05) body condition score when compared with the other groups on d 42, and when compared to the 3-yr-old cows (P < 0.05) on d 84. Production of 4% fat corrected milk tended (P < 0.09) to be less at d 0 for 2-yr-old than for mature cows, and on d 42 and 84, 4% fat corrected milk production of 2-yr-old cows was less (P < 0.05) than both 3-yr-old and mature cows (4.19, 6.74, and 6.28 kg/d for 2-yr, 3-yr, and mature cows respectively; SEM = 1.17). These data suggest that primiparous Braford heifers calving at 2 yr of age tend to produce approximately 25% less milk and direct more energy for gain than heifers calving for the first time at 3 yr of age.