Artificially extended photoperiod administered to pre-partum mares via blue light to a single eye: Observations on gestation length, foal birth weight and foal hair coat at birth

Abstract

In seasonally breeding animals, photoperiod perception is crucial for timing of important physiological events. In the horse, long day photoperiod influences the onset of ovulation and cyclicity, shedding of the heavier winter coat and the timing of parturition. In this compilation of studies, conducted across three breeding seasons and two countries, the impact of artificially extended day length was investigated on gestation length, foal birth weight and foal hair coat at birth. The light therapy was administered to pre-partum mares via mobile head worn masks which provided short wavelength blue light to a single eye. In Study 1, reductions in gestation lengths were observed following administration of artificially extended day length (124.8 ± 15.11 days) in the final months of pregnancy to a group of Thoroughbred mares compared to controls (P < 0.05; 339.7 ± 9.56 days vs 350.6 ± 9.13). Study 2 revealed that pre-partum exposure to artificially extended day length (104.6 ± 9.89 days) increased foal birth weight compared to controls (47.13 ± 2.93 kg vs 43.51 ± 6.14 kg; P < 0.05) in mares bred early in the year. In Study 3, artificially extended day length (87.53 ± 19.6 days) administered to pre-partum mares affected the coat condition of foals at birth with respect to hair weight (P < 0.0001) and hair length (P < 0.0001) compared to controls (0.34 ± 0.20 μg vs 0.59 ± 0.12 μg and 1.93 ± 0.56 cm vs 2.56 ± 0.32 cm, respectively). Collectively, these studies serve to highlight the influential role of the circa-annual changes in photoperiod length on the pre-partum mare for normal foetal development during the natural breeding season. It also emphasizes the potential that exists to improve breeding efficiency parameters by artificially simulating this important environmental cue in the latter stages of gestation against the backdrop of an economically driven early breeding season.

The effects of inbreeding on covering success, gestation length and foal sex ratio in Australian thoroughbred horses

“…5). Our findings agree with previous studies [12,30,32] and highlight the importance of photoperiod length for inducing parturition in horses [37]. This pattern may strongly depend on the mare's location, as photoperiod variation is highly dependent on the proximity to the equator.…”

Effect of environmental factors and changes in the body condition score on the onset of the breeding season in mares

“…It was suggested that changes in body composition may occur as a result of strengthened circadian rhythmicity of peripheral clocks and better internal synchronization that were the result of the abundance of (blue) light during daytime (Murphy & O'Brien, ). Moreover, in recent years, it has been demonstrated that blue light is the essential signal for entrainment of circadian rhythm in mares (Murphy et al, ; Nolan et al, ; Walsh et al, , ). Manipulation of the photoperiod using artificial blue light results in an earlier onset of cyclicity in the spring, reduced duration of pregnancy, increased birthweight of foals and changes in hair coat at birth (Murphy et al, ; Nolan et al, ).…”

“…Moreover, in recent years, it has been demonstrated that blue light is the essential signal for entrainment of circadian rhythm in mares (Murphy et al, ; Nolan et al, ; Walsh et al, , ). Manipulation of the photoperiod using artificial blue light results in an earlier onset of cyclicity in the spring, reduced duration of pregnancy, increased birthweight of foals and changes in hair coat at birth (Murphy et al, ; Nolan et al, ). The spectral qualities of different light sources (incandescent light, fluorescent light and direct natural sunlight) are significantly different from each other with natural daylight having the highest proportion of biologically effective short wavelength blue light (Murphy, ).…”

“…In recent studies on the impact of circadian rhythm on athletic performance in racehorses, researchers reported that both the quantity and quality of light during the natural daytime has a significant impact on the body composition and on the circadian clock gene expression in horses in training (Murphy & O'Brien, 2018 (Murphy & O'Brien, 2018). Moreover, in recent years, it has been demonstrated that blue light is the essential signal for entrainment of circadian rhythm in mares Nolan et al, 2017;Walsh et al, 2013Walsh et al, , 2014. Manipulation of the photoperiod using artificial blue light results in an earlier onset of cyclicity in the spring, reduced duration of pregnancy, increased birthweight of foals and changes in hair coat at birth Nolan et al, 2017).…”

Fatores que influenciam o tempo de gestação em éguas – Revisão de literatura

“…A utilização das máscaras de luz azul (Nolan et al, 2017) como ferramenta de aumentar o fotoperíodo nas éguas gestantes promoveu redução do TG e incrementou o processo de adaptação inicial do potro neonato. O único estudo até o presente momento no hemisfério sul com a utilização de iluminação artificial convencional, apresentou resultado diferente.…”