The decrease in milk yield during once daily milking is due to regulation of synthetic activity rather than apoptosis of mammary epithelial cells in goats

Abstract

<jats:p>Once daily milking (ODM) is a management practice that can improve working conditions and reduce production costs in dairy farming compared with twice daily milking (TDM). However, ODM is associated with a decrease in milk yield. Previous research indicated that disruption of tight junctions in the mammary gland may be one of the regulatory factors involved in the milk yield decrease observed during ODM. The aim of this study was to investigate the involvement of mammary epithelium disruption in the regulation of the activity and dynamics of mammary epithelial cells (MEC) during 5 weeks of ODM in goats. Twelve alpine goats (producing 3.67 ± 0.64 kg/day and 47 ± 1.6 days in milk) were assigned to two groups that were milked once or twice a day during 5 weeks and then switched back to TDM. Mammary biopsies were collected before and on days 2 and 16 of both ODM and TDM switchback periods. Milk purified epithelial cells were collected before and on days 1, 7, 21 and 28 during ODM as well on days 1 and 7 of the TDM switchback period. The mRNA levels of genes involved in the regulation of synthetic activity and apoptosis were analysed by RT-PCR in milk MEC and mammary biopsies. ODM decreased yields of milk (−23%), lactose (−23%) and casein (−16%). Lactose synthesis was regulated at the transcriptional level by downregulation of α-lactalbumin mRNA levels in both biopsy samples (−30%) and milk MEC (−74%). TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labelling) staining of mammary gland biopsies did not show any increase in cell apoptosis after 2 and 16 days of ODM (0.8% and 1%, respectively) despite upregulation of Bax mRNA levels in milk MEC. This suggests that the decrease in milk yield observed during ODM is attributable to a decrease in synthetic activity rather than to induction of MEC cell death. ODM induced the disruption of tight junctions in the mammary gland only on the first day of the treatment as indicated by increased blood lactose concentration. This indicates that the decrease in MEC activity observed over the 5 weeks of ODM was not due to disruption of the mammary gland tight junctions. There was no carryover effect of 5 weeks of ODM on milk production. Therefore, it appears that the decrease in milk yield that occurs during ODM in goats is due to regulation of synthetic activity rather than to apoptosis of MEC.</jats:p>

Biosynthesis of milk fat, protein, and lactose: roles of transcriptional and posttranscriptional regulation

“…The expression of LALBA increases upon treatment with a cocktail of lactogenic hormones (i.e., insulin ϩ hydrocortisone ϩ prolactin ϩ 17␤-estradiol or growth hormone), as observed in mouse and bovine mammary cells in vitro (105,199). The expression of LALBA is also induced by increased milking frequency in bovine and caprine (21,154) and by the AA Lys and Met in primary bovine mammary cells (155), but it is decreased by mastitis in dairy cow and yak (126,150) and by feed restriction in the cow (62). It is well established that the promoter region of LALBA contains a STAT5 binding site, and the presence of STAT5 is essential for the expression of LALBA in mouse (178,245).…”

Expression Profiling of Glucose Transporter 1 (GLUT1) and Apoptotic Genes (BAX and BCL2) in Milk Enriched Mammary Epithelial Cells (MEC) in Riverine Buffalo during Lactation

“…In such samples, the expression of genes related to milk production and mammary gland physiology may not provide a true representation (14). Comparatively, milk enriched MEC can be a potential and noninvasive alternative to biopsies from mammary tissues for studying cell specific expression of key genes associated with lactation (13,15) and provide a more precise reflection of mammary gland for studies related to milk synthesis (16)(17)(18)(19)(20)(21). Riverine buffalo (Bubalus bubalis) is a major milk producing species in many Asian and Mediterranean countries and its genetic improvement ranks high among agricultural research needs of these countries.…”

“…The rate of cell proliferation and apoptosis are the key processes that maintain equilibrium of MEC in the mammary gland during lactation (10,27). The expression of BAX and BCL2 genes and BAX=BCL2 ratio were calculated as indicative of the apoptotic rate in MEC harvested at different time points of lactation (1,14,21). Furthermore, BAX and BCL2 expression in milk MEC had been correlated with the decrease in milk yield during daily milking (13,21,22 (Fig.…”

Unilateral once daily milking locally induces differential gene expression in both mammary tissue and milk epithelial cells revealing mammary remodeling

“…Moreover a comparison of gene expression in both mammary tissue and milk-purified MEC has only been performed for a small number of genes: essentially coding for milk proteins and stearoyl-CoA desaturase (SCD) (4, 13, 25, 36). Our previous study showed a downregulation of ␣-lactalbumin (LALBA) transcripts after ODM in both milk-purified MEC and tissue samples from goats (4).…”

“…By contrast, apoptosis has been studied in goat mammary tissue but inconsistent results were obtained. Indeed, whereas apoptosis was demonstrated in one study (33), two others did not observe apoptosis when examined by terminal deoxynucleotidyl transferase-mediated 2=-deoxyuridine 5=-triphosphate nick-end labeling (TUNEL) staining (4,11). Furthermore, it is unknown whether ODM affects mammary cell proliferation.…”