Document Detail

Effect of continuous milking and bovine somatotropin supplementation on mammary epithelial cell turnover.
MedLine Citation:
PMID:  17183085     Owner:  NLM     Status:  MEDLINE    
Objectives were to determine effects of continuous milking (CM) and bovine somatotropin (bST) administration on 1) mammary epithelial cell (MEC) proliferation, apoptosis, and ultrastructure during late gestation and early lactation, 2) expression of genes associated with proliferation, and apoptosis in mammary epithelial cells, and 3) milk yield and composition. Second-gestation, first dry-period cows were randomly assigned to either continuous bST throughout late gestation and early lactation (+bST; n = 4) or no bST (-bST; n = 4) administration. Within each animal, udder halves were randomly assigned to CM or a 60-d dry period (control) treatment. Daily milk yield and weekly milk composition were measured during the last 60 d of gestation in CM halves and from 1 to 30 d postpartum for both halves. Mammary biopsies were obtained at -20 +/- 7, -8 +/- 3, +1 +/- 0, +7 +/- 0, and +20 +/- 0 d (mean +/- standard error) relative to parturition. Prepartum half-udder milk yield was greater in +bST cows than in -bST cows (9.9 vs. 8.2 kg/d) and postpartum half-udder milk yields were dramatically reduced in CM halves compared with control halves (10.6 vs. 22.2 kg/d), regardless of bST treatment. Proliferation of MEC was reduced in CM halves at -8 d (2.7 vs. 5.4%). Apoptosis of MEC was elevated during early lactation for d +1 and +7 in control halves, but was only increased at d +1 in CM halves. Turnover of MEC was not affected by bST. Ultrastructure data indicated complete involution of the control half and lactation maintenance in CM glands (d -20). By d -8, control tissue contained alveoli in an immature secretory state, but CM tissue contained both lactating and immature alveoli. Postpartum ultrastructure parameters were similar between halves until d 20 when control tissue was composed of a homogeneous population of lactating alveoli, but CM tissue contained lactating, engorged, and resting alveoli. Expression of CCAAT/enhancer binding protein-beta (CEBP-beta), cyclin D1, and bcl(2) were up-regulated during late gestation, but did not differ between control and CM halves. Expression of alpha-lactalbumin was increased in CM halves during late gestation, but was not different in CM and control tissue after parturition. Other genes evaluated (bax, insulin-like growth factor binding protein 5, ATP-binding cassette 1, and p27) were not differentially expressed at any timepoints evaluated. Results indicate that CM reduced subsequent half-udder milk yield in primiparous cows through altered MEC turnover and secretory capacity. Negative effects of CM on the subsequent lactation were not alleviated by bST supplementation.
E L Annen; A C Fitzgerald; P C Gentry; M A McGuire; A V Capuco; L H Baumgard; R J Collier
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Journal of dairy science     Volume:  90     ISSN:  1525-3198     ISO Abbreviation:  J. Dairy Sci.     Publication Date:  2007 Jan 
Date Detail:
Created Date:  2006-12-21     Completed Date:  2008-09-12     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  2985126R     Medline TA:  J Dairy Sci     Country:  United States    
Other Details:
Languages:  eng     Pagination:  165-83     Citation Subset:  IM    
Department of Animal Sciences, University of Arizona, Tucson 85721, USA.
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MeSH Terms
Apoptosis / physiology
Cattle / physiology*
Cell Proliferation
Dairying / methods
Dietary Supplements*
Epithelial Cells / cytology*,  physiology,  ultrastructure
Gene Expression Regulation / physiology
Growth Hormone / administration & dosage*
Lactation / physiology
Mammary Glands, Animal / cytology*,  physiology*,  ultrastructure
Milk / chemistry,  secretion
Postpartum Period
Reverse Transcriptase Polymerase Chain Reaction
Time Factors
Reg. No./Substance:
89383-13-1/growth hormone, bovine; 9002-72-6/Growth Hormone

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