Equine Health Update Issue 1 Volume 16 - Page 18

During long days the inhibitory action of melatonin on the mare’s reproductive axis is lifted and increased gonadotropin releasing hormone pulse frequency stimulates the anterior pituitary to release follicle stimulating hormone and luteinising hormone, which act in concert to promote the growth, development and ovulation of ovarian follicles [9–11]. The northern hemisphere specifies a universal birthday for Thoroughbred racehorses of 1 January. Breeders therefore desire foals born early in the year to produce mature yearlings and precocious 2-yearold racehorses. Studies show that annual earnings are significantly higher for horses born in January– February than for those born in April–June [12,13]. For breeders to satisfy industry timelines, it is necessary that they manipulate the mares’ reproductively active period to meet the official start date of the breeding season on 15 February. Beginning 1 December, it has become standard industry practice to extend day length for 8–10 weeks by exposing mares to artificial light until 23.00 h, allowing natural dawn to occur during the most sensitive phase of the 24 h cycle [4]. An artificial photoperiod of 16 h light: 8 h dark is facilitated using light from a 100 W light bulb in a 3.6 °— 3.6 m stall [3,14], loosely described as ‘enough light to read a newspaper’. Light therapy such as this can advance the breeding season by as much as 3 months [15]. Recent research indicates that light within the short-wavelength spectrum (465–485 nm) is most effective at inhibiting melatonin [16] as melanopsin is particularly sensitive to short wavelength, blue light [17,18]. A recent study in Thoroughbred mares has shown that melatonin can be successfully inhibited using low-level blue light (465 nm) from a light emitting diode (LED) source directed at a single eye [19]. We aim to determine if timed, low-intensity, blue light administered to a single eye from head worn light masks is as effective as indoor maintenance under white light at advancing the breeding season in mares. Materials and methods Animals All experimental procedures were approved by the University College Dublin Animal Research Ethics Committee and the University of Kentucky Institutional Animal Care and Use Committee protocol number 2012-0928. Healthy, Thoroughbred mares (n = 59), all aged between 5 and 24 years, were used for this experiment. All mares included in the study had a body condition 18 score between 4 and 6 using the Henneke body condition scoring system [20] and there was no difference in average body condition score between groups (Group 1, 5.1 °” 0.7; Group 2, 5.1 °” 0.5; Group 3, 4.8°” 0.5, P>0.05). The experiment took place on 2 farms located in Fayette County, Lexington, Kentucky. Group 1 (n = 16) was kept in a large pasture during the day and housed indoors in individual stalls at night. Group 2 (n = 25) was maintained in 2 groups in large pastures during the day and night. Group 3 (n = 19) was maintained on a separate farm, within an 8 km radius of the first, as a group in a large pasture during both day and night. There was no difference between the age ranges of mares within the different groups (Group 1, 12.6 °” 4.9; Group 2, 13.1 °” 4.4; Group 3, 11.4 °” 4, P>0.05). The experiment took place from 20 November 2011 to 10 February 2012 at longitude W -84.4° and latitude N 38.1°, which experienced temperatures that ranged from -10.6 to 20.6°C during this period. During the experiment Group 1 grazed ad libitum during the day and had ad libitum access to hay at night. In addition, this groupwas supplemented with either 2.7 kg/day of a low-starch diet; Purina Wellsolve Lo