Effect of exogenous somatotropin in Holstein calves on mammary gland composition and proliferation

Abstract

Pubertal mammary gland growth and development are hormonally regulated, but the details are poorly understood in calves. Our purpose was to evaluate the effects of exogenous growth hormone (GH) on the biochemical composition of the prepubertal mammary gland, mRNA expression of selected genes, and histological characteristics of the developing parenchyma (PAR). In this experiment, 19 calves (7 ± 4 d of age) were randomly assigned to 1 of 2 treatments: bovine somatotropin (bST, 500 mg; n = 10) or placebo (Sal; 0.9% saline; n = 9). Animals were treated every 3 wk beginning on d 23. Calves were assigned to an early (65 d; tissue harvested after 2 treatment injections) or late collection time (107 d; tissue harvested after 4 treatment injections). Calves were fed milk replacer and calf starter for 8 wk and starter and hay thereafter. Parenchyma and mammary fat pad (MFP) from one udder half were harvested for analysis of protein, lipid, and DNA. Additional tissues were preserved for histological analysis or snap-frozen for quantitative real-time PCR. Somatotropin treatment did not significantly alter the mass of PAR or MFP or the general pattern of development of epithelial structures. Significant increases were observed in protein/100 kg of body weight (BW), total protein, DNA concentration, DNA/100 kg of BW, and total DNA in 107-d calves, and a significant treatment by day interaction was observed for DNA and lipid concentrations in PAR. In MFP, a significant decrease was observed in protein/100 kg of BW in bST-treated calves and in total MFP protein in 65-d calves. A treatment by day interaction was found for total protein, DNA, and protein/100 kg of BW. In PAR, relative expression of ATPase-binding cassette 3 and growth hormone receptor were reduced by bST and both were lower in 107-d-harvest calves. Epithelial cell retention of bromodeoxyuridine (BrdU; possible indicator of stem-like cells) was greatest in 65-d bST-treated calves, and a significant time of sampling response and treatment × time interaction were observed. Expression of the proliferation marker protein Ki67 was numerically higher in bST-treated calves but the difference was nonsignificant. Retention of the BrdU label was reduced in 107-d calves. Exogenous growth hormone given to calves may affect mammary tissue composition and epithelial cell gene expression in subtle ways but exogenous supplementation with bST alone is not likely to alter overall development patterns or affect the mass of mammary parenchymal tissue. Whether such subtle changes have an effect on subsequent development or function is unknown.

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

“…This suggests that increased Epi expression could explain the dramatic impairments in ductular development that occurs in older ovariectomized heifers [28]. We also noted (Velayudhan et al [2]) that epithelial cell stratification in mammary ducts was reduced in ovariectomized calves in this trial.…”

“…All tissues used for these experiments were collected from two animal studies. In a first experiment, Huderson et al [2], 19 Holstein heifer calves were randomly assigned to either Posilac (bST; 500 mg of bST; n = 10; Monsanto Co., St Louis, MO) or Placebo (Sal; 0.9% saline; n = 9) treatment (Figure 1). Within treatment animals were assigned to an early (E) or late (L) harvest point.…”

“…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]).…”

“…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]). In contrast, ovariectomy of young prepubertal heifers decreased PAR accumulation and had an especially negative impact in heifers ovariectomized at the earliest age (Velayudhan et al [2]). The relative change in PAR mass between 30 and 90 days of age is dramatic, approximately a 60-fold [8].…”

“…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.…”