PS1-6. Observational Assessment of Preconception Energy Status on Daughters’ Lactation Traits in Canadian Holsteins.

Abstract Maternal perturbations around the time of conception may influence offspring growth, metabolism, and productivity; however, empirical evidence for such effects in dairy cattle remains limited. This study quantified the association between preconception maternal energy status and daughters’ lactation performance using routinely recorded indicators. Specifically, we evaluated the effects of dam energy status within 40 days before conception, assessed by milk fat-to-protein ratio (FPR) and energy-corrected milk herd deviation (EMHD), on daughters’ 305-day milk yield (305DMY), energy-corrected milk (ECM), fat-corrected milk (FCM), and fat- and protein-corrected milk (FPCM). Lactation records from 84,610 dam-daughter pairs across 2552 Quebec dairy herds were analyzed using linear mixed models. All model effects were statistically significant (P < 0.05). The model included dam-related factors such as days in milk (DIM) at conception (40–220 days), five quintile classes of FPR and EMHD, parity (five classes), and dam birth date as a covariate to account for temporal trends. Daughter-related factors included herd-year of calving (random effect), month of calving (January–December), and age at calving (19–78 months). For each maternal preconception indicator, the third quintile (40–60%) was used as the reference class, and all other estimates were expressed as deviations from this intermediate class. Dam EMHD exhibited a consistent positive association with all daughter lactation traits. Daughters born to dams with higher preconception EMHD—reflecting above-herd-average metabolic output during the preconception window—produced greater 305DMY, ECM, FCM, and FPCM. In contrast, dam FPR showed a different pattern in association with daughter performance. Daughters’ ECM, FCM, and FPCM increased as dam FPR rose to an intermediate threshold (1.26–1.36), beyond which performance declined, indicating a potential optimal preconception FPR range for daughter productivity. Conversely, daughter 305DMY declined progressively with increasing dam FPR, likely reflecting dilution effects on milk volume rather than solids-adjusted traits. Overall, the results demonstrate variability in preconception dam energy-status indicators and provide evidence that maternal preconception energy status contributes to daughters’ lactation performance. Incorporating preconception maternal effects—particularly those related to energy status—may reduce bias in breeding value estimation and enhance the accuracy of selection decisions. These findings underscore the importance of biologically informed modeling approaches in quantifying preconception maternal influences and advancing our understanding of how early maternal conditions shape lifetime lactation performance in dairy cattle.