188 Supplementation of individual heifers to target precision growth curves in developing beef heifers grazing dormant forage.

Abstract In the Northern Great Plains, developing heifers are commonly grazed on dormant native rangeland. Optimizing growth and development is critical for heifer reproductive success, and individual variation in supplement intake can alter growth trajectories, resulting in unmet developmental goals. The integration of precision technology and nutrition models allows for individual supplementation and to monitor growth and nutrition during heifer development. The objective of this study was to evaluate precision feeding technology and individual nutrition models to achieve individual growth, body composition, and development targets in replacement Angus heifers. Angus heifers (n = 47, BW = 201.12 ± 32.99 kg) were weaned in September 2024 from the Cottonwood Research Station Cowherd (mature BW = 650 Kg), near Philip, SD. Each heifer was fitted with a radio frequency identification and a biometric tracking tag (701x, Fargo, ND). Following a 45-d backgrounding period, heifers were moved to native pasture (208.5 ha). There were 2 waterers (Cobett®, Lorimar, IA) within the pasture, each equipped with a scale (SmartScales®), open circuit gas flux system (GreenFeed®), and a precision feeder (SuperSmartFeed Producer®, C-Lock Inc., Rapid City, SD). Data analysis was conducted in Program R. Individual supplementation targets were created using a precision nutrition model designed to facilitate individuals to achieve 60% of estimated mature BW (390 kg) by the May 1st breeding period. Heifers were stratified by BW to assess the effect of diverging nutritional plains and were assigned to 1 of 3 supplementation strategies: Low, Constant, or High (75, 100, or 125%, respectively) of estimated individual supplement required for the first half of the supplementation period. BW at the start of the trial on November 26 was 221.5 ± 37.71kg when treatments were assigned. To achieve growth goals, small BW heifers were placed into the continuous growth treatment group due to biological limitations for individual feed consumption, resulting in both the low and high treatment groups having significantly higher (60.3 vs 52.9 kg respectively, p < 0.05) initial BW. Bio-metric data was used to assess growth bi-weekly and adjust individual assigned supplement allowance. Daily supplement intake data indicated 28% of heifers consumed within 10% of their supplement allowance, while 30.8% over-consumed by 32% and the remaining 41% of heifers under-consumed by 46.3%. A linear regression model between desired and realized heifer growth rates resulted in an R2 of 0.23. This study demonstrates the opportunity to integrate nutrition models with precision livestock technology to target individual animal growth and development outcomes. However, more research is needed to improve the accuracy and precision of individual animal nutrition requirements and improve the reliability of precision feeding systems.