Crossbred ewe lambs were used in a 2 X 2 X 2 factorial design to deter
mine the effect of ovariectomy, age, and estrogen administration on pr
epuberal mammary development. Intact (I, n = 20) and ovariectomized (O
VX, n = 17) lambs were sacrificed at 6 and 13 wk of age after 1 wk of
either estrogen 0.1 mg/kg BW/day, s.c.) or vehicle injections. Ovariec
tomies were performed at 10 +/- 1 d of age. At sacrifice, one mammary
gland was dissected into parenchymal and stromal fractions for biochem
ical analyses. Parenchymal explants from the remaining gland were labe
led with [H-3]thymidine for histoautoradiography. Neither ovariectomy
nor estrogen treatment affected body weight, total gland weight, or pa
renchymal weight (P > 0.05). However, means for each of these variable
s increased between 6 and 13 wk (P < 0.01). Analysis of relative mamma
ry growth showed significant positive deviations from isometry. Howeve
r, no significant difference in parenchymal allometry was observed bet
ween I and OVX groups. Exogenous estrogen stimulated an increase (P <
0.05) in epithelial cell labeling with [H-3]thymidine, but neither ova
riectomy nor age at sacrifice had any effect (P > 0.2) on epithelial l
abeling. These results demonstrate that prepuberal allometric mammary
growth in the ewe lamb does not require the presence of the ovary. (C)
Elsevier Science Inc. 1998.