Skip to main content
ARS Home » Research » Publications at this Location » Publication #220095
Title: Effects of increased milking frequency on gene expression in the bovine mammary gland

Author
item Connor, Erin
item SIFERD, STEPHEN - EXPRESSION ANALYSIS
item Elsasser, Theodore
item Clover, Christina
item Van Tassell, Curtis - Curt
item Sonstegard, Tad
item FERNANDES, VIOLET - 1265-09-00
item Capuco, Anthony

Submitted to: BMC Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/27/2008
Publication Date: 8/20/2008
Citation: Connor, E.E., Siferd, S., Elsasser, T.H., Clover, C.M., Van Tassell, C.P., Sonstegard, T.S., Fernandes, V., Capuco, A.V. 2008. Effects of increased milking frequency on gene expression in the bovine mammary gland. Biomed Central (BMC) Genomics. 9:362.

Interpretive Summary: It has been shown that milking dairy cattle 4× daily during the first few weeks of lactation can enhance milk yield, and that the effect persists throughout the entire lactation period, even if animals are returned to a 2× daily milking schedule. The specific mechanisms controlling this increase in milk production are unknown. In the present study, we used two gene transcript profiling methods to identify changes in gene expression in the mammary gland of dairy cows milked 4× daily milking beginning at day 4 of lactation (IMF4) relative to glands milked 2× daily (Control) to gain a better understanding of changes occurring within the gland during more frequent milking. Our results suggest that increased milk yield during increased milking frequency may be mediated or complemented by enhanced mammary extracellular matrix remodeling and blood vessel development within the gland. Additional study is needed to determine whether these changes result in increased milk yield, or occur in response to an increased demand for milk production. Gene pathways identified by the current study will provide a basis for future studies to identify factors mediating the effects of milking frequency on milk yield.

Technical Abstract: Previous research has demonstrated that increased milking frequency of dairy cattle during the first few weeks of lactation enhances milk yield, and that the effect persists throughout the entire lactation period. The specific mechanisms controlling this increase in milk production are unknown, but suggested pathways include increased mammary epithelial cell number, secretory capacity, and sensitivity to lactogenic hormones. In the present study, we used serial analysis of gene expression (SAGE) and microarray analysis to identify changes in gene expression in the bovine mammary gland in response to 4× daily milking beginning at d 4 of lactation (IMF4) relative to glands milked 2× daily (Control) to gain insight into physiological changes occurring within the gland during more frequent milking. Total RNA used for analysis was extracted from mammary biopsies obtained at approximately d 7 of lactation from multiparous Control (n = 3) and IMF4 cows (n = 3 to 4). Results indicated changes in gene expression related to cell proliferation and differentiation, extracellular matrix (ECM) remodeling, metabolism, nutrient transport, and immune function in IMF4 versus Control cows. In addition, pathways expected to promote neovascularization within the gland appeared to be up regulated in IMF4 cows. To validate this finding, immunolocalization of Von Willebrandt's factor (VWF), an endothelial cell marker, and its co-localization with the nuclear proliferation antigen Ki67 were evaluated in mammary tissue sections at approximately d 7 and d 14 of lactation in cows milked 4× daily versus Controls to estimate endothelial cell abundance and proliferation within the gland. Consistent with expression of genes related to neovascularization, both abundance of VWF and its co-localization with Ki67 appeared to be elevated in cows milked 4× daily, suggesting increased milk yield during increased milking frequency may be mediated or complemented by enhanced mammary ECM remodeling and neovascularization within the gland. Additional study is needed to determine whether these changes result in increased milk yield, or occur in response to an increased demand for milk production. Gene pathways identified by the current study will provide a basis for future investigations to identify factors mediating the effects of milking frequency on milk yield.