Expression of genes involved in regulation of cell turnover during milk stasis and lactation rescue in sow mammary glands

We studied the transcription of selected genes involved in the regulation of cell turnover during milk stasis and lactation rescue in individual mammary glands of sows and evaluated the timeframe for lactation rescue and the subsequent productivity of rescued glands. Suckling was prevented in two glands from each of five sows by taping them the day after farrowing for 1 or 3 d (Closed 24 h and Closed 72 h glands, respectively). After removing the tape, Closed 24 h glands were suckled until weaning. Closed 72 h glands were refused by the piglets and therefore remained unsuckled. Mammary gland biopsies were collected to quantify the transcription of genes involved in cell turnover and the percentage of proliferating and apoptotic cells. Transcriptional data were analyzed with a [gamma]-distributed generalized linear mixed model. Mammary transcription of [alpha]-lactalbumin was high in suckled glands the day after farrowing, indicating onset of lactation, but was downregulated after 1 d of milk stasis. The prolac-tin receptor mRNA was downregulated and IGFBP-5 mRNA was upregulated within 1 d of milk stasis. The downregulation of [alpha]-lactalbumin and prolactin receptor and upregulation of IGFBP-5 mRNA noted after 1 d of milk stasis was maintained in Closed 72 h glands (those glands regressed) but reversed on d 4 and 6 of lactation in Closed 24 h glands. Mammary IGF-I mRNA was not regulated in response to milk stasis or lactation rescue. The percentage of proliferating cells in mammary glands was high prepartum (13.1%) and intermediate (7.8%) the day after farrowing. By d 6 of lactation, the percentage of proliferating cells was increased to 10.1% (P < 0.01) in glands suckled regularly but decreased to 5.9% (P < 0.05) in regressing glands (Closed 72 h glands). Glands rescued after 1 d of milk stasis had lower productivity throughout lactation than glands suckled regularly, as indicated by the BW of piglets suckling these glands (242 vs. 315 g/d, respectively; P < 0.05). In conclusion, regularly suckled glands had a greater cell proliferation, greater transcriptions of [alpha]-lactalbumin and prolactin receptor genes, and less IGFBP-5 transcription compared with rescued (Closed 24 h) and regressing (Closed 72 h) glands. Glands that were not suckled for 1 d could be rescued, although their subsequent productivity was lower, whereas glands not suckled for 3 d could not be rescued.