Environmental and genetic effects on hematologic characteristics of beef cows

The objective of this study was to determine the effects of certain environmental and genetic factors on selected hematologic characteristics of beef cows under wintering and grazing conditions in the Northeast. Packed cell volume PCV, hemoglobin concentration (Hb), RBC count, and WBC count were determined in serial blood samples collected periodically during 1976 from 24 young and mature, gestating and lactating, Angus and Angus-Charolais cows. The PCV, Hb, and RBC were significantly correlated (P < 0.001, n = 257; rPCV . Hb = 0.89, rPCV. RBC = 0.74, rHb . RBC = 0.72). Lactating cows grazing mixed swards containing 24% legume had higher (P < 0.001) PCV and Hb than did cows grazing all-grass swards fertilized with 168 kg of nitrogen/ha. The RBC was higher (P < 0.01) in cows grazing all-grass swards, whereas no differences in WBC were observed between groups. Angus cows had lower PCV (P < 0.001) and RBC (P < 0.005) than did Angus-Charolais cows. Individual cows of identical physiologic maturity-breed-diet groups differed (P < 0.05) in PCV, Hb, RBC, and WBC, indicating that there are repeatable differences in these traits among individual cows. Significant effects of season and physiologic state (pregnancy vs lactation) were observed for PCV, Hb, RBC, and WBC (P < 0.01).