Changes in Whole Blood Parameters in Beef Heifers May Contribute to Delayed Pubertal Attainment

Pubertal development in beef heifers is a transient period that has many contributing factors. Previously in our lab, progesterone (P4) concentrations collected from heifers at weaning (Oct) to breeding (May) were used to identify four distinct pubertal groups: Typical, Early, Start-Stop, and Non-Cycling. There is limited research on heifers and the impacts of whole blood cell populations, particularly WBCs, during pubertal development; however, girls with differing puberty onset displayed altered concentrations of hematocrit, white blood cells (WBC), and hemoglobin concentrations. Thus, our hypothesis was that heifer pubertal groups with delayed or precocious puberty may have increased white blood cells or altered whole blood parameters contributing to abnormal pubertal development. Weekly blood samples during the pre and peripubertal period were collected to obtain progesterone concentrations from previously identified pubertal classifications. Monthly blood samples were also analyzed with a HemaTrue ® Veterinary Hematology Analyzer to determine whole blood parameters. Additionally, blood smears were used to count specific WBC populations. All blood parameters were found to change during the collection period suggesting that weight and maturity directly impacts hematological and immunological factors. Early heifers tended to have reduced granulocyte cells (p=0.07) when compared to Typical (controls) but was not different from Start-Stop and Non-Cycling. Additionally, red cell distribution width to platelet ratio tended to be greater in Early compared to Typical and Non-Cycling heifers. Early and Start-Stop heifers that initiate puberty earlier had increased hematocrit (p=0.04) when compared to heifers with delayed puberty (Non-Cycling). Finally, Non-Cycling, heifers had reduced hemoglobin levels (p=0.03) compared to all other pubertal groups. Thus, hematological factors such as reduced granulocytes, increased hematocrit, and increased red blood cell width per platelet number may promote increased growth and development resulting in the probability that heifers will initiate puberty earlier. Furthermore, reductions in hemoglobin concentrations or functionality may delay pubertal attainment. Advisor: Andrea S. Cup