title: Blue light from individual light masks directed at a single eye advances the breeding season in mares.
abstract: BACKGROUND
  Artificial lighting is commonly used to advance the breeding season in horses. Light masks have been developed that direct light at a single eye to inhibit the production of melatonin, the decoder of photoperiod for seasonally breeding animals.
  
  
  OBJECTIVE
  To investigate whether low-intensity blue light from light masks was effective at advancing the breeding season in mares.
  
  
  METHODS
  Controlled experiment.
  
  
  METHODS
  Data on reproductive activity was collected from 3 groups of mares maintained on Kentucky horse farms under various lighting conditions between 20 November 2011 and 10 February 2012: 59 nonpregnant, healthy Thoroughbred mares were used. On 1 December 2011, Group 1 (n = 16) was housed indoors under barn lighting (250 Lux) until 23.00 h daily. Group 2 (n = 25) wore light masks programmed to turn on from 16.30 h until 23.00 h daily and was maintained outdoors. Group 3 (n = 19) was maintained outdoors under the natural photoperiod as control. At 2-week intervals, rectal ultrasound examinations were performed and blood was collected for progesterone analysis. Oestrous cyclicity was defined as the presence of follicles >20 mm diameter detected in conjunction with serum progesterone >1 ng/ml and confirmation of ovulation by transrectal ultrasound examination.
  
  
  RESULTS
  On 10 February, the number of mares exhibiting oestrous cyclicity was 14/16 (87.5%) in Group 1; 20/25 (80%) in Group 2; and 4/19 (21%), in Group 3. Pairwise comparison of groups revealed no difference in the number of cycling mares between Groups 1 and 2 (χ(2) test, P = 0.3348) whereas differences were observed between Groups 1 and 3 (χ(2) test, P<0.0001) and Groups 2 and 3 (χ(2) test, P<0.0003).
  
  
  CONCLUSIONS
  Low-intensity blue light to a single eye from a light mask is an effective alternative to maintenance of mares indoors under lights for advancing the breeding season. Mobile light therapy for horses could have economic benefits for the breeder by reducing the costs of maintaining mares indoors, and welfare benefits for horses by permitting outdoor maintenance.
authors.affiliation: School of Agriculture and Food Science, University College Dublin, Ireland.
authors.forename: B A
authors.initials: BA
authors.lastname: Murphy
authors.forename: C M
authors.initials: CM
authors.lastname: Walsh
authors.forename: E M
authors.initials: EM
authors.lastname: Woodward
authors.forename: R L
authors.initials: RL
authors.lastname: Prendergast
authors.forename: J P
authors.initials: JP
authors.lastname: Ryle
authors.forename: L H
authors.initials: LH
authors.lastname: Fallon
authors.forename: M H T
authors.initials: MH
authors.lastname: Troedsson
mesh_terms: D000818:Animals; D003116:Color; D030762:Estrous Cycle / Q000528:radiation effects*; D005260:Female; D006736:Horses / Q000502:physiology*; D008027:Light; D014730:Veterinary Medicine / Q000295:instrumentation*
keywords: blue light; horse; light mask; melatonin; progesterone; seasonality