Abstract Developing heifers are often managed in drylot systems to facilitate estrous synchronization protocols. Transitioning heifers from a drylot to a grazing environment immediately after insemination reduces pregnancy success. Changes in diet around the time of conception affect the uterine environment and developing embryo, impacting embryonic survival. Yet, research investigating effects of different heifer management strategies prior to breeding on offspring growth is limited. The objective of this project was to investigate the impact of drylot and pasture management systems on AI conception rates and offspring growth through weaning. Crossbred beef heifers (n = 813) were weaned and wintered in the drylot receiving a forage-based diet. Once spring forage was available, half of the heifers were moved to pasture while the other half remained in the drylot for synchronization. Heifer BW were recorded at pre-breeding (d -50), breeding (d 0), and at pregnancy diagnosis (d + 106). Heifers that remained in the drylot (DLT) were synchronized with the Select Synch protocol. Heifers managed on pasture (PST) were observed for behavioral estrus for 21 d and artificially inseminated 12 h after observed estrus. At the conclusion of synchronization and breeding, DLT heifers were transported to pasture. Heifers were exposed to clean-up bulls for 60 d post-AI. Initial heifer BW was not different at pre-breeding between DLT and PST heifers (405 ± 2 kg vs. 408 ± 2 kg; P 0.1). From pre-breeding to breeding, DLT heifers gained 0.77 kg/d while PST heifers gained 0.07 kg/d (P 0.05). From breeding to palpation, DLT heifers lost 0.10 kg/d while PST heifers gained 0.17 kg/d (P 0.05). Palpation BW was not different between management groups (P 0.1). Pregnancy data were analyzed using the GLIMMIX procedure in SAS. Conception rates via AI were 36.78 ± 2.4% for DLT heifers and 52.16 ± 2.4% for PST heifers (P 0.05). Overall pregnancy rates were 85.89 ± 1.8% for DLT heifers and 88.46 ± 1.6% for PST heifers and were not different by management group (P 0.1). Offspring analysis was completed on heifers who conceived to AI, gave birth, and weaned a calf (n = 321). Offspring birth BW and weaning BW were analyzed using GLM procedures in SAS. At birth, there was no difference based on management group for offspring BW (P 0.1). Weaning BW was influenced by a sex × management interaction (P = 0.056). Male calves from PST dams had the greatest weaning BW (205.4 ± 2.3 kg) compared with males from DLT dams (187.6 ± 2.9 kg) and female calves from both management groups (187.4 ± 2.0 kg). These data show altering heifer trajectory of gain during pre-breeding through early pregnancy can ultimately impact offspring growth performance through weaning.
Hauxwell et al. (Wed,) studied this question.