UVM Theses and Dissertations
Format:
Print
Author:
Wright, John B.
Dept./Program:
Animal Sciences
Year:
2010
Degree:
MS
Abstract:
In dairy cows, frequent milking during early lactation stimulates an increase in milk yield that partly persists throughout the remainder of lactation. Recent reports evaluating the milk yield response to frequent milking in primiparous heifers and multiparous cows and its effect on somatic cell count (SCC) have been inconsistent, and it is unknown what effect increasing milking frequency has on teat end callosity thickness (TECT), and udder edema. Furthernore, the mechanism by which frequent milking increases milk production is unknown. It is well established that milk production is a function of mammary epithelial cell number and activity, suggesting increasing milking frequency during early lactation increases one or both of these factors. Interestingly, frequent milking increases exposure of the mammary gland to honnones released during milking, which may promote mammary cell proliferation, survival, or function during lactation. Oxytocin is a key honnone of interest as plasma concentrations are higher in cows subjected to frequent milking during early lactation, and oxytocin receptor has been localized to mammary epithelial cells.
Thus, it is plausible that oxytocin may regulate gene expression in mammary epithelial cells, and facilitate the increase in milk yield in response to increased milking frequency. Specifically, oxytocin may influence expression of genes involved in the IGF-axis, a well-known regulator of mammary function. The goals of this study were to quantify the effects of unilateral frequent milking [UFM; twice daily milking (2X) of the left udder half, four-times daily milking (4X) of the right udder half] on primiparous Holstein heifers, and investigate oxytocin as a potential mechanism in regulating the increase in milk yield associated with increased milking frequency during early lactation. We hypothesized that UFM of primiparous heifers would stimulate an acute and persistent increase in milk production and decrease udder edema in 4x udder halves, with no effect on TECT. In addition, we hypothesized, that oxytocin would alter expression of genes encoding insulin-like growth factor-lor its binding proteins in cultured bovine mammary epithelial cells, leading to increased mammary epithelial cell number or activity.
Primiparous heifers were assigned at parturition to UFM for days 1 to 21 of lactation. By day 21 of lactation, 4x udder halves produced 2.75 ± 0.33 kg/d more milk than 2x udder halves (P <0.01). Upon cessation of UFM, 4x udder halves continued to produce 0.88 ± 0.33 kg/d more milk than 2x udder halves through day 270 of lactation (P <0.05). Udder edema, TECT, and SCC were unaffected by UFM. To investigate the response of bovine mammary epithelial cells to exogenous oxytocin, the MAC-T, BME-UV1, and BME-UV2 cell lines were treated with oxytocin and analyzed for changes in mRNA expression through quantitative reversetranscription (qRT)-PCR, and cell proliferation. In the MAC-T cell line expression of IGFBP-4 was down regulated in response to treatment with oxytocin (1[Greek mu]M) for 24 hours (P <0.05), however this response could not be reliably reproduced in subsequent experiments. Proliferation was not affected by treatment with oxytocin (1[Greek mu]M) for 24 or 48 hours (P> 0.12). If oxytocin down regulates mammary IGFBP-4 in vivo, increased levels of oxytocin in response to increased milking frequency may increase exposure of the mammary epithelium to IGF and contribute to the observed milk yield response.
Thus, it is plausible that oxytocin may regulate gene expression in mammary epithelial cells, and facilitate the increase in milk yield in response to increased milking frequency. Specifically, oxytocin may influence expression of genes involved in the IGF-axis, a well-known regulator of mammary function. The goals of this study were to quantify the effects of unilateral frequent milking [UFM; twice daily milking (2X) of the left udder half, four-times daily milking (4X) of the right udder half] on primiparous Holstein heifers, and investigate oxytocin as a potential mechanism in regulating the increase in milk yield associated with increased milking frequency during early lactation. We hypothesized that UFM of primiparous heifers would stimulate an acute and persistent increase in milk production and decrease udder edema in 4x udder halves, with no effect on TECT. In addition, we hypothesized, that oxytocin would alter expression of genes encoding insulin-like growth factor-lor its binding proteins in cultured bovine mammary epithelial cells, leading to increased mammary epithelial cell number or activity.
Primiparous heifers were assigned at parturition to UFM for days 1 to 21 of lactation. By day 21 of lactation, 4x udder halves produced 2.75 ± 0.33 kg/d more milk than 2x udder halves (P <0.01). Upon cessation of UFM, 4x udder halves continued to produce 0.88 ± 0.33 kg/d more milk than 2x udder halves through day 270 of lactation (P <0.05). Udder edema, TECT, and SCC were unaffected by UFM. To investigate the response of bovine mammary epithelial cells to exogenous oxytocin, the MAC-T, BME-UV1, and BME-UV2 cell lines were treated with oxytocin and analyzed for changes in mRNA expression through quantitative reversetranscription (qRT)-PCR, and cell proliferation. In the MAC-T cell line expression of IGFBP-4 was down regulated in response to treatment with oxytocin (1[Greek mu]M) for 24 hours (P <0.05), however this response could not be reliably reproduced in subsequent experiments. Proliferation was not affected by treatment with oxytocin (1[Greek mu]M) for 24 or 48 hours (P> 0.12). If oxytocin down regulates mammary IGFBP-4 in vivo, increased levels of oxytocin in response to increased milking frequency may increase exposure of the mammary epithelium to IGF and contribute to the observed milk yield response.