Effects of maternal influence and season on immune phenotype and stress response of calves from selected sires

In recent decades, intensified selection pressure on livestock for economically important traits, such as growth, has led to a decline in overall robustness. Beef cattle play a vital role in the U.S. food system and economy; however, they frequently encounter various stressors stemming from environmental conditions, including heat stress, nutritional deficiencies, pests, pathogens, and management practices like handling, weaning, transportation, and commingling. These stressors can adversely affect animal health, well-being, and productivity. Furthermore, individual animals perceive stress differently due to differences in genetic makeup and past experiences, which can lead to varied effects on other biological functions, including the immune system and gut microbiome. It is essential to gain a deeper understanding of how environmental and management-related stressors affect the immune phenotype of beef cattle. Such insights could guide breeding strategies considering paternal production traits and other factors affecting the offspring’s ability to thrive across diverse environmental conditions. The first study evaluated the stress responses and immune phenotypes in steer calves sired by bulls selected for superior growth and milk traits, considering the calving season, from initial processing through a month in the feedlot. The second study further investigated stress responsiveness by utilizing additional stress biomarkers alongside cortisol in steer and heifer calves. The third study focused on a subset of steer calves to analyze gut microbiota using 16S rRNA sequencing of fecal DNA, examining the effects of genetic selection, maternal factors, and calving season post-weaning through the 60-day preconditioning phase. Finally, building on these insights, the last study investigated the interplay between maternal characteristics and sire growth traits during both spring and fall calving seasons to assess their collective impact on immune phenotype, stress responsiveness, and maternal role in vaccine efficacy. These findings revealed that rigorous selection for production traits, maternal factors such as previous experiences, and seasonal challenges differentially impact calf stress responses, immune phenotypes and gut microbiomes. Although further research is necessary to elucidate the underlying mechanisms and other environmental conditions, future breeding strategies should integrate additional biological elements, including maternal traits, production goals, and seasonal factors, to better support calf health and well-being.