286 Impact of rate of overwinter gain in March-born yearling range heifers on growth rates and reproductive performance

Abstract Our objective was to determine the impact of rate of overwinter gain in March-born yearling heifers on pre- and post-breeding growth rates and reproductive performance. Red Angus x Simmental crossbred beef heifers n = 182; weaning body weight (BW) = 242 kg ± 23 kg were utilized in a 3-yr study conducted at the University of Nebraska, Gudmundsen Sandhills Laboratory (GSL) near Whitman, NE. Using 3-d BW averages collected in January, heifers were stratified by BW and randomly assigned to one of two treatments: 1) to achieve a low overwinter rate of gain at 0.34 kg/d (LO, n = 106), or 2) to achieve a high overwinter rate of gain at 0.68 kg/d (HI, n = 76). To achieve gains, heifers were managed together and had individual access to a dried distillers grain supplement via a C-lock Smart Feeder (Rapid City, SD). Each year, treatments were initiated in January and ended in May (111 ± 4 d). Heifer BW was collected at the start of trial (January), end of the trial (May), pre-breeding (May), pregnancy diagnosis (October), and pre-calving (February). Heifer body condition score (BCS) was collected at pregnancy diagnosis (October) and pre-calving (February; Yr 1 and 2). Before the breeding season, two blood samples were collected 10-d apart via coccygeal venipuncture to determine the percentage of heifers cycling. At breeding, HI-fed heifers had a greater (P 0.01) BW than LO-fed heifers (813 and 788 kg, respectively; Table 1). However, heifer BW at pregnancy diagnosis and pre-calving were not impacted (P ≥ 0.16) by supplemental treatment. Additionally, there were no differences (P ≥ 0.16) in BCS at pregnancy diagnosis and pre-calving among treatments. Furthermore, rate of gain did not influence (P ≥ 0.38) the percent pubertal prior to the breeding season, pregnancy rates, or the percent that calved in the first 21-d of the calving season. Moreover, rate of gain did not impact (P = 0.89) subsequent calf BW at birth. There was a significant treatment x year interaction (P 0.01) for subsequent calving date, where HI treatment heifers calved 7-d earlier than LO treatment heifers in Yr 1. This study implies that producers can develop heifers at a less overwinter rate of gain without impacting reproductive performance or subsequent calf birth weight.