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

Author
item GALINDO-GONZALEZ, S - UNIVERSITY OF FLORIDA
item ARTHINGTON, J - UNIVERSITY OF FLORIDA
item Coleman, Samuel
item DE VRIES, A - UNIVERSITY OF FLORIDA

Submitted to: Professional Animal Scientist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/24/2006
Publication Date: 12/1/2006
Citation: Galindo-Gonzalez, S., Arthington, J.D., Coleman, S.W., De Vries, A. 2006. Case Study: Evaluation of Milk Production and Energy Partitioning in Primiparous Braford Heifers Calving at Two-vs. Three- Years of Age.. Professional Animal Scientist. 22:467-471.

Interpretive Summary: Beef heifers in the tropics and subtropics are traditionally bred to calve for the first time at three years of age. However, breading yearlings to calve first as two-year olds should be a good strategy to begin the recover of the costs associated with development and to increase lifetime productivity. The purpose of this study was to determine differences in energy utilization as well as performance of Braford heifers calving for the first time at two vs. three yr of age at a similar nutrition. Mature Braford cows were included for comparison. Feed intake was regulated so that two- and three-year old cows would gain 0.22 kg/d and mature cows would maintain weight. Weight change, milk production, and body condition score were recorded for the cows. Results showed that mature cows lost weight, three year olds maintained, and two-year olds gained weight during the study. Two-year old heifers were fatter, but produced 25% less milk than three-year olds because they directed more energy for gain. The lower level of milk production would translate in lighter calf weaning weight. The strategy to calve heifers first at two years of age may increase nutritional pressure that restricts energy available for lactation, and possibly reproduction.

Technical Abstract: Twelve cows and their calves were selected from 3 age groups (n = 4 pairs/age group), consisting of 2-and 3 yr-old and mature 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. Back fat thickness was measured on d 0 and 84 using ultra-sound. 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 3yr-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 4, 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.