Abstract #W54

Section: Beef Species
Session: Beef Species
Format: Poster
Day/Time: Wednesday 7:30 AM–9:30 AM
Location: Gatlin Ballroom
# W54
The effect of selection using residual average daily gain EPD on growth and reproductive performance in Angus heifers.
J. B. Wells*1, J. R. Segers1, J. Duggin1, J. K. Bertrand1, R. Rekaya1, T. D. Pringle1, 1University of Georgia, Athens, GA.

Forty-five heifers were produced at the Northwest Georgia Research and Education Center in Calhoun from the random mating of commercial Angus cows to Angus bulls selected for high and low residual ADG (RADG) EPD and high and average marbling EPD. The experimental design was a 2 × 2 factorial design with 2 Angus sires represented in each of the following treatments: high RADG, high marbling (Hi/Hi); high RADG, average marbling (Hi/Avg); low RADG, high marbling (Lo/Hi); and low RADG, average marbling (Lo/Avg). Heifers from the matings were studied to determine the effects of selection for RADG and marbling on growth and reproductive performance. Heifer weights were recorded and composition was determined via ultrasound scanning at 229 d (weaning) and 391 d (yearling) of age. There were no differences observed in weaning and yearling weights between the groups (P > 0.19). Weaning 12th rib fat levels were different with low RADG animals having greater fat depth (P = 0.01) than high RADG. Interactions between RADG and marbling were present in yearling 12th rib fat (P = 0.04), weaning IMF (P = 0.07), and yearling IMF (P = 0.08) with Lo/Avg heifers having greater values than Hi/Avg heifers. Blood samples were drawn at 8 mo, 10 mo, and 12 mo of age to directly quantify the level of progesterone present using the Siemens Coat-A-Count Progesterone RIA procedure. At 10 mo of age, 26% of low RADG heifers had reached puberty while no high RADG heifers had reached puberty. By 12 mo of age, 37% of low RADG and 19% of high RADG heifers had reached puberty. At approximately 14 mo of age, heifers were synchronized and artificially inseminated using the 14-d CIDR-PG & TAI protocol. Heifers that returned to estrus within 30 d were bred a second time by AI before exposure to a bull. Overall AI conception rates were Hi/Hi: 82%, Hi/Avg: 53%, Low/Hi: 89%, and Low/Avg: 80%. The average age at calving (714 d) was not different between groups (P = 0.73). In conclusion, selection using RADG may negatively effect early reproductive performance in Angus heifers, however, further work is needed to fully characterize the potential for this trait as a selection tool in beef production systems.

Key Words: residual ADG, heifer, reproduction