title: The effects of milking frequency on insulin-like growth factor I signaling within the mammary gland of dairy cows.
abstract: In dairy cows, short-term changes in milking frequency (MF) in early lactation have been shown to produce both an immediate and a long-term effect on milk yield. The effect of MF on milk yield is controlled locally within mammary glands and could be a function of changes in either number or activity of secretory mammary epithelial cells (MEC). Insulin-like growth factor I (IGF-I) signaling is one candidate factor that could mediate these effects, as it can be controlled locally within mammary glands. Both MEC number and activity can be affected by IGF-I signaling by activating the phosphoinositide 3-kinase (PI3K)/Akt and extracellular-signal-regulated kinase (ERK)1/2 pathways. To investigate the relationship between MF and IGF-I signaling, udder halves of 17 dairy cows were milked either 4 times a day (4×) or once a day (1×) for 14 d in early lactation. On d 14, between 3 and 5 h following milking, mammary biopsies were obtained from 10 cows from both udder halves, and changes in the expression of genes associated with IGF-I signaling and the activation of the PI3K/Akt and ERK1/2 pathways were measured. The mRNA abundance of IGF type I receptor, IGF binding protein (IGFBP)-3, and IGFBP-5 were lower following 4× milking relative to 1× milking. However, the mRNA abundance of IGF-I was not affected by MF. Both IGFBP3 and IGFBP5 are thought to inhibit IGF-I; therefore, decreases in their mRNA abundance may serve to stimulate the IGF-I signal in the 4×-milked mammary gland. The activation of PI3K/Akt pathway was lower in response to 4× milking relative to 1×, and the activation of the ERK1/2 was unaffected by MF, suggesting that they do not mediate the effects of MF.
authors.affiliation: AgResearch Ltd., Ruakura Research Centre, PB 3123, Hamilton 3240, New Zealand; Institute of Agriculture and Environment, College of Sciences, Massey University, PB 11222, Palmerston North 4442, New Zealand. Electronic address: regan.murney@agresearch.co.nz.
authors.forename: R
authors.initials: R
authors.lastname: Murney
authors.affiliation: SciLactis Ltd., Waikato Innovation Park, Hamilton 3240, New Zealand.
authors.forename: K
authors.initials: K
authors.lastname: Stelwagen
authors.affiliation: AgResearch Ltd., Ruakura Research Centre, PB 3123, Hamilton 3240, New Zealand.
authors.forename: T T
authors.initials: TT
authors.lastname: Wheeler
authors.affiliation: Institute of Agriculture and Environment, College of Sciences, Massey University, PB 11222, Palmerston North 4442, New Zealand.
authors.forename: J K
authors.initials: JK
authors.lastname: Margerison
authors.affiliation: AgResearch Ltd., Ruakura Research Centre, PB 3123, Hamilton 3240, New Zealand.
authors.forename: K
authors.initials: K
authors.lastname: Singh
mesh_terms: D000818:Animals; D017209:Apoptosis; D002417:Cattle; D049109:Cell Proliferation; D003612:Dairying; D004847:Epithelial Cells / Q000378:metabolism; D005260:Female; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism*; D007774:Lactation / Q000502:physiology; D008321:Mammary Glands, Animal / Q000378:metabolism*; D008892:Milk; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011897:Random Allocation; D017526:Receptor, IGF Type 1 / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D018972:Insulin-Like Growth Factor Binding Protein 3; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D019869:Phosphatidylinositol 3-Kinases; D017526:Receptor, IGF Type 1; D051057:Proto-Oncogene Proteins c-akt
keywords: cell signaling; mammary; milk synthesis; milking frequency