Influence of timing of gain on growth and reproductive performance of beef replacement heifers.

Our objective was to determine whether beef heifers could be developed by delaying the majority of weight gain until the last third of the developmental period before the onset of the breeding season. Spring-born Angus x Hereford heifers were used in each of two consecutive years and were allotted at weaning to gain either .45 kg/d for the entire developmental period (yr 1 = 159 d, n = 40; yr 2 = 168 d, n = 40; EVENGAIN) or to gain .11 kg/d from d 0 to 112, followed by .91 kg/d from d 112 to 159 (yr 1, n = 40) or d 168 (yr 2, n = 40; LATEGAIN). Body weights and condition scores were determined at d 0, 112, and 159 (yr 1) or d 0, 112, and 168 (yr 2). Heifers were subjected to a 60-d breeding season. Frame scores and pelvic areas were determined at the conclusion of the breeding season. Actual daily gains for EVENGAIN heifers for yr 1 and yr 2 were .60 and .51 kg/d, respectively. LATEGAIN heifers gained .25 and .05 kg/d during the restricted phases from d 0 to 112, followed by 1.14 and 1.32 kg/d during the accelerated growth phases for yr 1 and 2, respectively. Body weight at the onset of the breeding season and weight at puberty were not different between treatments in either year. Age at puberty did not differ in yr 1, but, age at puberty in yr 2 was delayed (P < .01) in LATEGAIN (406.9 d) compared to EVENGAIN (386.3 d) heifers. The LATEGAIN and EVENGAIN heifers had similar pelvic areas, frame scores, and body condition scores in each year. First-service conception rates of both groups were similar in yr 1 (55.5 vs 55.3%). In yr 2, LATEGAIN heifers tended (P = .18) to have an increase in first-service conception rate compared to EVENGAIN heifers (71.1 vs 56.4%). No treatment differences occurred in either average age of conception or overall pregnancy rates at the conclusion of the breeding season for either year. The LATEGAIN heifers were developed to a similar BW on 12 (P < .01) and 2.5% (not statistically significant) less feed for yr 1 and 2, respectively, compared to EVENGAIN heifers. We interpret these data to indicate that delaying the majority of weight gain until late in heifer development may decrease costs without detrimental effects on reproductive performance.