Effect of a Biological Response Modifier on Expression of Growth Factors and Cellular Proliferation at Drying Off

Invited review: Accelerating mammary gland involution after drying-off in dairy cattle

Bovine mammary gland involution, as a part of the reproductive cycle in dairy cows, is a very important remodeling transformation of the mammary gland for the subsequent lactation. There is considerable incentive to accelerate mammary gland involution to improve udder health, shorten the dry period, and simplify the management process by reducing dietary changes. The complex process of mammary involution is characterized by morphological changes in the epithelial cells and mammary tissue, changes in the composition of mammary secretions, and changes in the integrity of tight junctions. Involution is facilitated by elements of the immune system and several types of proteases and is coordinated by various types of hormones. This review first describes the involution process and then argues for the need to accelerate it. Last, this review focuses on various intervention methods for accelerating involution. Our aim is to provide a comprehensive overview of bovine mammary gland involution as well as potential techniques and new opinions for dry cow management.

Proliferation-apoptosis balance inStaphylococcus aureuschronically infected bovine mammary glands during involution

The objective of this study was to determine whetherStaphylococcus aureuschronic intramammary infection (IMI) influences expression of proteins related to regulation of proliferation and apoptosis processes and proliferation/apoptosis index during active involution in bovine mammary gland. Twenty-one Holstein non-pregnant cows in late lactation either uninfected or with chronic naturally acquiredS. aureusIMI were included in this study. Cows were slaughtered at 7, 14 and 21 d after cessation of milking and samples for immunohistochemical analysis were taken. Protein expression of Bcl-2, Bax, Fas and active caspase-3 in mammary tissue was significantly affected by chronicS. aureusIMI, all showing increased immunoexpression inS. aureus-infected quarters at all involution stages. The percentage of apoptotic cells was increased by IMI in both mammary parenchyma and stroma, and the percentage of parenchymal and stromal cell proliferation was also increased. The proliferation/apoptosis ratio was significantly increased by IMI only in stromal cells. This imbalance to favour proliferation inS. aureus-infected mammary quarters could be one of the underlying causes that induce aberrant involution with permanence of nonsecretory tissue and increase of stromal components.

Cellular proliferation rate and insulin-like growth factor binding protein (IGFBP)-2 and IGFBP-3 and estradiol receptor alpha expression in the mammary gland of dairy heifers naturally infected with gastrointestinal nematodes during development

Mammary ductal morphogenesis during prepuberty occurs mainly in response to insulin-like growth factor-1 (IGF-1) and estradiol stimulation. Dairy heifers infected with gastrointestinal nematodes have reduced IGF-1 levels, accompanied by reduced growth rate, delayed puberty onset, and lower parenchyma-stroma relationship in their mammary glands. Immunohistochemical studies were undertaken to determine variations in cell division rate, IGF-1 system components, and estradiol receptors (ESR) during peripubertal development in the mammary glands of antiparasitic-treated and untreated Holstein heifers naturally infected with gastrointestinal nematodes. Mammary biopsies were taken at 20, 30, 40, and 70 wk of age. Proliferating cell nuclear antigen immunolabeling, evident in nuclei, tended to be higher in the parenchyma of the glands from treated heifers than in those from untreated. Insulin-like growth factor binding proteins (IGFBP) type 2 and type 3 immunolabeling was cytoplasmic and was evident in stroma and parenchyma. The IGFBP2-labeled area was lower in treated than in untreated heifers. In the treated group, a maximal expression of this protein was seen at 40 wk of age, whereas in the untreated group the labeling remained constant. No differences were observed for IGFBP3 between treatment groups or during development. Immunolabeling for α ESR (ESR1) was evident in parenchymal nuclei and was higher in treated than in untreated heifers. In the treated group, ESR1 peaked at 30 wk of age and then decreased. These results demonstrate that the parasite burden in young heifers negatively influence mammary gland development, affecting cell division rate and parameters related to estradiol and IGF-1 signaling in the gland.

Intramammary inoculation of Panax ginseng extract in cows at drying off enhances early mammary involution

This study was designed to evaluate the effects of a single intramammary infusion of Panax ginseng extract on cell proliferation and death mechanism in bovine mammary gland during early involution. Eight mammary quarters from six non-pregnant cows in late lactation were infused with 10 ml of ginseng solution (3 mg/ml), six quarters were treated with 10 ml of placebo (vehicle alone) and six quarters were maintained as uninoculated controls. Milking was interrupted after infusion. Animals included in the three groups were slaughtered 7 d after inoculation and samples for histological analysis were taken. Morphometric analysis showed a significant increase in percentages of mammary tissue area occupied by stroma in ginseng-treated quarters compared with controls. A significant increase of immunostained area for bax protein and active caspase-3 was observed in ginseng-treated quarters compared with controls, whereas no differences were observed for bcl-2 immunostaining. Expression of bax mRNA was significantly higher in ginseng-treated quarters than in controls. The bax/bcl-2 ratio indicated a significant predominance of bax over bcl-2 mRNA expression in ginseng-treated quarters compared with controls. The rise of epithelial and stromal cell apoptosis in situ by TUNEL was more marked in quarters treated with ginseng than in controls. Ginseng inoculation had no effect on the number of epithelial and stromal proliferating cells labelled with Ki-67 antibody. Ratio of apoptotic to proliferating cells was higher in quarters treated with ginseng compared with controls, indicating a net loss of cells in parenchymal components. Also, the intramammary inoculation of ginseng extract at drying off increased the rate of mammary cell apoptosis without inhibiting cell proliferation. Taken together, these changes are indicative of mammary regression enhancement during early involution.

The role of estrogen receptors, erbB receptors, vascular endothelial growth factor and its receptors, and vascular endothelial growth inhibitor in the development of the rat mammary gland

We identified the localization and distribution of cell-specific epidermal growth factor receptors (EGFRs: erbB-1, erbB-2, erbB-3, erbB-4), vascular endothelial growth factor (VEGF), VEGF receptors [VEGFRs: VEGF-R1 (flt-1), VEGF-R2 (flk-1/KDR), VEGF-R3 (flt-4)], vascular endothelial growth inhibitor (VEGI), and estrogen receptor (ER), and determined whether or not these growth factors in rat mammary glands are functional. Thirty-five adult female Spraque-Dawley rats were randomly divided into five groups, each of which were at the 7th, 14th, and 21st day of pregnancy; 7th day post-delivery; and 7th day after weaning. It was determined that erbB, VEGF and its receptors, VEGI, and ER stained at different intensities. Intense staining was observed, in particular, in erbB receptors during pregnancy and involution, and also in VEGF and its receptors during lactation, while ER stained during the last periods of pregnancy and lactation. In conclusion, the expression of erbB, VEGF and its receptors, and ER were determined at varying intensities at different sites of the mammary gland during pregnancy, lactation, and involution periods.

Effect of a biological response modifier on cellular death mechanisms at drying off

Agents that increase natural protective mechanisms have been proposed for prevention and treatment of intramammary infections. The objective of this study was to describe the effects of a single intramammary infusion of a lipopolysaccharide (LPS)-based biological response modifier (BRM) on cellular death mechanism in uninfected andStaphylococcus aureus-infected bovine mammary glands during involution. Three groups of 12 cows, each one including 6Staph. aureus-infected and 6 uninfected, were infused in two mammary quarters with BRM or placebo and slaughtered at 7, 14 and 21 d of involution. In infected quarters, BRM treatment produced a significant increase in percent of stained epithelial cells for the apoptosis-promoting protein Bax at every observation period. In addition, BRM produced a significant increase of immunostained stromal cells for Bax compared with placebo-treated quarters. BRM treatment produced an increase in percentages of epithelial cells staining with active caspase-3 at 7 d and 14 d of involution compared with placebo-treated quarters and a significant decrease in percentages of terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL)-positive epithelial cells at 7 d and 21 d of involution. In addition, BRM treatment caused an increase in percentage of stromal cells immunostaining for active caspase-3 and TUNEL. An increase of active caspase-3 and TUNEL epithelial and stromal cell immunostaining was observed inStaph. aureus-infected compared with uninfected quarters. Cellular proliferation, determined by Ki-67 immunostaining, was increased in epithelial and stromal cells fromStaph. aureus-infected compared with uninfected quarters at every observation period. These results provide new insights into the mechanism of mammary cell death in uninfected andStaph. aureus-infected bovine mammary gland during involution and illustrate the effects of LPS-based BRM on apoptosis and cell proliferation during mammary involution.