INFLUENCE OF TIMING OF GAIN ON GROWTH AND REPRODUCTIVE-PERFORMANCE OFBEEF 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 d evelopmental period before the onset of the breeding season. Spring-bo rn 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 d evelopmental period (yr 1 = 159 d, n = 40; yr 2 = 168 d, n = 40; EVENG AIN) 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 weig hts and condition scores were determined at d 0, 112, and 159 (yr 1) o r 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 conclusio n 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 ga ined .25 and .05 kg/d during the restricted phases from d 0 to 112, fo llowed 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 sea son and weight at puberty were not different between treatments in eit her year. Age at puberty did not differ in yr 1, but, age at puberty i n yr 2 was delayed (P < .01) in LATEGAIN (406.9 d) compared to EVENGAI N (386.3 d) heifers. The LATEGAIN and EVENGAIN heifers had similar pel vic 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 increas e 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 breedin g season for either year. The LATEGAIN heifers were developed to a sim ilar BW on 12 (P < .01) and 2.5% (not statistically significant) less feed for yr 1 and 2, respectively, compared to EVENGAIN heifers. We in terpret these data to indicate that delaying the majority of weight ga in until late in heifer development may decrease costs without detrime ntal effects on reproductive performance.