Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
10974220 | Journal of Dairy Science | 2015 | 7 Pages |
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 (4Ã) or once a day (1Ã) 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 4Ã milking relative to 1Ã 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 4Ã-milked mammary gland. The activation of PI3K/Akt pathway was lower in response to 4Ã milking relative to 1Ã, and the activation of the ERK1/2 was unaffected by MF, suggesting that they do not mediate the effects of MF.
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Authors
R. Murney, K. Stelwagen, T.T. Wheeler, J.K. Margerison, K. Singh,