Submitted to: Livestock Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 25, 2006
Publication Date: December 1, 2006
Citation: Akers, R.M., Capuco, A.V., Keys, J.E. 2006. Cellular differentiation in mammary tissue of beef and dairy heifers. Livestock Science. 105:44-49.
Interpretive Summary: A comparative histological analysis of mammary tissue from a beef (Hereford) and dairy (Holstein) breeds was performed to evaluate differences in the mammary tissues that might relate to selection for increased milk production. Tissues were obtained during gestation and lactation. Mammary tissue from dairy cows contained a greater percentage of secretory cells and associated lumenal area and lower percentage of connective tissue elements than did tissue from beef cows. Based upon histological criteria of secretory activity, lactating mammary tissue from dairy cows contained a greater percentage of actively secreting epithelial cells than did tissue from beef cows. Data support the hypothesis that selection for milk production has been accompanied by an increase in total number of secretory cells as well as increase the secretory activity of individual cells.
Quantitative histology of mammary parenchymal tissue from 16 Hereford and 16 Holstein heifers was determined for tissue obtained on day 150, 180, and 280 of gestation and on day 49 of lactation. Percent area occupied by stromal tissue was progressively decreased on each consecutive sample day during gestation in Herefords and was lower in both breeds during lactation. Overall, area occupied by stromal tissue elements was also greater in Herefords. Percent lumenal space and number of alveolar cells per cross section was consistently greater for Holsteins and increased across sample periods in both breeds. More than 40% of the alveolar cells in Herefords were characterized as poorly differentiated but in Holstein heifers nearly all of the cells were classified as either intermediate or fully differentiated. These data provide additional evidence to support the idea that much of the difference in milk production between beef and dairy animals depends on increased mammary function. Whether similar effects occur when Holsteins selected for milk production are compared with Holsteins that less intensively selected for milk production remains to be determined.