Effects of body weight and nutrition on histological mammary development in Holstein heifers

Representative image of heifer mammary tissue at 10× magnification stained with hematoxylin and eosin.

Image of mammary tissue from a 100-kg heifer (upper panel) and a 350-kg heifer (lower panel). The bar in both images equals 50μm. Differences in tissue complexity are illustrated by the marked difference in the number of epithelial structures per field.

Number of epithelial and luminal structures present in an 871,820μm² area of the mammary parenchyma taken from heifers reared on either an elevated (E; 950g/d of ADG; n=32; open bars) or a restricted (R; 650g/d of ADG; n=34; filled bars) diet across all slaughter weights. Values shown are least squares means for epithelial (SEM 2.9 and 2.8 for E and R, respectively) and luminal structures (SEM 2.5 and 2.4, for E and R, respectively); values tended to differ by diet (P<0.1, luminal; P<0.1, epithelial).

Number of epithelial (upper panel) and luminal structures (lower panel) present per image (871,820μm² of mammary parenchyma) in tissue sections from heifers slaughtered at different BW (100, 150, 200, 250, 300, or 350kg of BW). Values are least squares means for heifers fed either a restricted (R) or elevated (E) diet. The linear trends for changes in the number of structures per field were significant (P<0.001).