JDS
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Journal of Dairy Science Vol. 74 No. 6 1821-1829
© 1991 by American Dairy Science Association ®
This Article
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Evans, N. M.
Right arrow Articles by Hoover, J.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Evans, N. M.
Right arrow Articles by Hoover, J.

Effect of Chronobiological Alteration of the Circadian Rhythm of and Prolactin and Somatotropin Release in the Dairy Cow

N. M. Evans 1, R. R. Hacker 1, and J. Hoover 1

1 Department of Animal and Poultry Science, University of Guelph, Guelph, ON, Canada N1G 2W1

The objective of this study was to determine if a skeletal photoperiod administered at the appropriate time of a 24-h day could stimulate prolactin and somatotropin release in dairy cattle. Cows in mo 8 of gestation were exposed to either 12 to 13 h of continuous light or to three skeletal photoperiods consisting of a total of 8 h of light. Cows in the skeletal photoperiod light regimens received 6 h of light from 0500 to 1100 h and a 2-h light pulse at either 1500 to 1700 h, 1800 to 2000 h, or 2100 to 2300 h. Cows exposed to the light regimen pulse at 1800 to 2000 h exhibited a circadian rhythm of prolactin and somatotropin release. The mean prolactin and somatotropin concentrations were also higher in this treatment. It is concluded that a circadian rhythm with a photosensitive phase is present for prolactin and somatotropin release in the lactating dairy cow. The photosensitive phase for both hormones occurs between 13 and 15 h after subjective dawn. The expression of the circadian rhythm of these hormones depends on the photoperiod to which cows are exposed.

Key Words: circadian rhythm • plactin • somatotropin

Submitted on July 18, 1990
Accepted on January 18, 1991




This article has been cited by other articles:


Home page
 J DAIRY SCIHome page
R. Muller and L. Schrader
Individual Consistency of Dairy Cows' Activity in Their Home Pen
J Dairy Sci, January 1, 2005; 88(1): 171 - 175.
[Abstract] [Full Text] [PDF]

Home page
 J DAIRY SCIHome page
M. Rodriguez, D. Petitclerc, D.H. Nguyen, E. Block, and J.F. Burchard
Effect of Electric and Magnetic Fields (60 Hz) on Production, and Levels of Growth Hormone and Insulin-Like Growth Factor 1, in Lactating, Pregnant Cows Subjected to Short Days
J Dairy Sci, November 1, 2002; 85(11): 2843 - 2849.
[Abstract] [Full Text] [PDF]


HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Copyright © 1991 by the American Dairy Science Association ®.