Effect of staged ovariectomy on measures of mammary growth and development in prepubertal dairy heifers

Abstract

Previous studies in prepubertal heifers suggest that the magnitude of reduction in mammary parenchymal growth in response to ovariectomy varies with the age at which surgery is performed. We hypothesized that ovarian secretions are essential for initiating mammary development but not required to maintain allometric mammary growth in prepubertal dairy heifers. The objectives of this study were to determine the effect of staged ovariectomy during the prepubertal period on mammary growth and tissue composition and the expression of selected genes. Prepubertal Holstein heifers at 2, 3 or 4 months of age were randomly assigned to one of two treatments, ovariectomized (OVX; n 5 12) or sham operated (INT; n 5 12). Mammary parenchyma (PAR) and fat pad (MFP) were harvested 30 days after surgery. Proximate composition of PAR and MFP (DNA, protein and lipid) as well as expression of the selected estrogen-responsive genes stanniocalcin1 (STC1), tissue factor pathway inhibitor precursor (TFPI) and proliferating cell nuclear antigen (PCNA) were determined in PAR and MFP by quantitative real-time PCR. The relative amount of epithelium and proportion of epithelia cell nuclei expressing the proliferation marker Ki67 were determined by histological and immunohistochemical analyses, respectively. MFP mass was not impacted by treatment but was decreased with age as was lipid content and concentration (P < 0.01). The mass of mammary PAR was reduced in OVX and increased with age (P < 0.01). Parenchymal tissue tended to have less total DNA, protein and lipid in OVX heifers. Parenchymal tissue concentrations of protein and DNA were increased with age and there was an age 3 treatment interaction. Treatment had no effect on either the Ki67 labeling index or percent epithelial area. The relative abundances of STC1, TFPI and PCNA mRNA in PAR were reduced in OVX. We did not find a significant impact of ovariectomy on mRNA expression when surgery was performed at 2 months compared with surgery at 3 or 4 months of age. However, having nearly undetectable PAR in two heifers ovariectomized at the earliest period (2 months of age) suggests that early ovariectomy is especially detrimental to subsequent parenchymal development.

Feeding a higher plane of nutrition and providing exogenous estrogen increases mammary gland development in Holstein heifer calves

“…Samples of fixed parenchymal tissue were embedded in paraffin and tissue sections subsequently prepared, dewaxed, and stained with hematoxylin and eosin for general histology as described in previous studies (Velayudhan et al, 2012;Tucker et al, 2016).…”

“…Moreover, mammary tissue in prepubertal ruminants is sensitive to E 2 (Woodward et al, 1993;Ellis et al, 1998;Capuco et al, 2002). Despite the fact that circulating concentrations of E 2 are very low in prepubertal calves (Purup et al, 1993;Velayudhan et al, 2012Velayudhan et al, , 2015 when E 2 influence is removed from the calf via ovariectomy or the use of an E 2 receptor antagonist, mammary gland development is markedly reduced (Berry et al, 2003;Tucker et al, 2016). Perhaps enhanced early nutrition augments the action of mammogenic stimuli (such as E 2 ); for this reason, we selected E 2 to test our hypothesis.…”

Effect of exogenous somatotropin and staged ovariectomy on mRNA expression of select ECM-related proteins in mammary tissue of prepubertal Holstein calves

“…One heifer was dropped from the study after harvest due to chronic illness. In a second experiment, Velayudhan et al [3], 20 Holstein heifer calves were randomly assigned to one of two treatments, ovariectomy (OVX; n = 8) or sham operation (INT; n = 12) (Figure 2). Surgeries were performed at 2, 3 and 4 months of age.…”

“…No other genes were affected by age or interaction between treatment and age. uated the effect of exogenous GH (bST) (Huderson et al [2]) and ovariectomy (Velayudhan et al [3]) on mammary gland composition, proliferation and histology in prepubertal heifers. In contrast with work on older animals [25], we found that for these very young prepubertal heifers, exogenous GH had minimal impact on several measures of mammary development including: PAR mass, histological appearance and rate of cell proliferation (Huderson et al [1]).…”

“…Despite the well-established importance of these hormones in bovine mammogenesis, understanding how these hormones impact expression of extracellular matrix (ECM) proteins of the prepubertal bovine mammary gland is unexplored. We took advantage of tissues collected from recent experiments which determined the effect of exogenous GH (Huderson et al [2]) and staged ovariectomy (Velayudhan et al [3]) on mammary development, to provide samples for this evaluation. Details on treatments, animal handling, and overall mammary development are available in these references.…”