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Animals 2015, 5(3), 803-820;

Evidence for a Role of Prolactin in Mediating Effects of Photoperiod during the Dry Period

Department of Animal Sciences, University of Illinois, Urbana, IL 61801, USA
College of Veterinary Medicine, University of Illinois, Urbana, IL 61802, USA
Department of Animal Science, University of Vermont, Burlington, VT 05405, USA
Current address: Pancosma S.A., Geneva, CH-1218, Switzerland
Current address: Division of Animal Sciences, University of Missouri, Columbia, MO 65211, USA;
Author to whom correspondence should be addressed.
Academic Editor: Àlex Bach
Received: 3 June 2015 / Revised: 21 July 2015 / Accepted: 7 August 2015 / Published: 19 August 2015
(This article belongs to the Special Issue Nutritional and Metabolic Health of Dairy Cow)
Full-Text   |   PDF [707 KB, uploaded 19 August 2015]   |  


Photoperiod manipulation during the lactation cycle alters milk yield, with long days (LDPP) increasing yield in lactation and short days (SDPP) in the dry period improving subsequent yield. Circulating prolactin (PRL) is directly related to day length, with LDPP increasing and SDPP decreasing PRL, respectively. Two blocks of 24 multiparous Holstein cows were used during two consecutive years to test the hypothesis that the mammary response to SDPP is the result of decreased concentrations of PRL in the circulation relative to LDPP. Cows were randomly assigned to one of three treatment groups during the dry period: SDPP, LDPP, or SDPP+PRL. Cows were returned to ambient photoperiod at calving and milk yield and DMI recorded for 120 d and 42 d, respectively. Mammary biopsies were obtained to determine rates of [3H]-thymidine incorporation into DNA in vitro. Treatment of SDPP cows with PRL caused a rapid increase in systemic PRL that reached concentrations similar to cows under LDPP. The periparturient PRL surge was similar for LDPP and SDPP+PRL cows, but those groups had greater surge concentrations versus SDPP. Cows exposed to SDPP produced more milk than LDPP cows, and there was a trend for SDPP+PRL cows to produce more milk than LDPP cows. Milk production was inversely related to the periparturient PRL surge. There was a trend for a treatment effect on mammary cell proliferation with greater proliferation in mammary tissue of SDPP cows relative to LDPP or SDPP+PRL on day −20 relative to parturition. Replacement of PRL to cows on SDPP when dry resulted in milk yield intermediate to cows on SDPP or LDPP, supporting the concept of a link between dry period PRL and yield. View Full-Text
Keywords: dry period; prolactin; photoperiod dry period; prolactin; photoperiod

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Crawford, H.M.; Morin, D.E.; Wall, E.H.; McFadden, T.B.; Dahl, G.E. Evidence for a Role of Prolactin in Mediating Effects of Photoperiod during the Dry Period. Animals 2015, 5, 803-820.

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