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

Abstract

Several methods have been proposed to advance the onset of the breeding season in horses. Most of them are based on the exposure to an artificial lighting period combined with hormonal treatments. Mares exposed to an artificial photoperiod are most often housed indoors where the ambient temperature is often higher than the outside temperature. Mares held in barns are also exposed to different daylight intensities than horses kept outside, depending on the architecture. In the current study, we evaluated the impact of ambient temperature, daylight intensity and changes in body condition score (BCS) on the timing of first ovulation after winter anestrus in mares exposed to an artificial photoperiod. Mares (n = 211) were housed in barns with different ambient temperature and daylight exposure but with the same artificial photoperiod exposure (except for a natural photoperiod control group). Artificial photoperiod as well as an increase in BCS over the winter significantly advanced the first spring ovulation. The BCS at the start and end of the anestrus period did not have an effect on the interval to first ovulation and neither did the modest increase in ambient temperature in the barn. However, a higher light intensity during the daytime significantly advanced the first spring ovulation. The results of this study suggest that exposure to more sunlight advances the onset of the breeding season. This effect is likely mediated through the biological effect of short wavelength blue light and its impact on melatonin suppression and biological rhythms. We suggest that greater/direct exposure to the blue light component of daylight improves the response to the artificial photoperiod. The results of the present study can further assist to optimize the conditions that lead to an efficient spring transition of breeding mares.

The effect of Equilume light masks on the timing of seasonal ovulation of Thoroughbred mares in South Korea

“…In contrast, Dini and coworkers reported that greater sun light exposure affects the timing of the breeding season in mares during artificial photoperiod treatment, while differences in barn temperature had no effect (Dini et al, 2019). In Thoroughbred yearlings, an extended photope riod activates gonadal hormones in both cold and warm climate (Suzuki et al, 2015).…”

Update on the management of anoestrus and transitional phase in horses

“…Their observations also suggested that exposure to more direct sunlight was beneficial for an early onset of reproductive activity, even if mares were more exposed to the prevailing environmental conditions. They also reaffirmed that an ‘interruption of the night’ with exposure to two hours of light approximately nine hours after dusk (beginning 15 December) hastened the mean interval to first ovulation by 58 days compared to those under natural lighting conditions (Dini and others 2019).…”

“…Research performed in Belgium by Dini and others (2019) demonstrated that mares that had an increase in body condition score between 19 December and 21 February ovulated earlier than mares that did not. Their observations also suggested that exposure to more direct sunlight was beneficial for an early onset of reproductive activity, even if mares were more exposed to the prevailing environmental conditions.…”

Effect of Tocopherol and Selenium on the Performance of Buserelin for Estrus Induction in Late Season Anestrus Mares (Equus Caballus)

“…Mares show anestrus behavior during short days of the year. Melatonin is a dark/sleep hormone, in short days its secretion increases, causing gonadotropin releasing hormone down regulation (Dini et al 2019). Decreased level of follicle stimulating hormone leads to decreased follicular growth & developments.…”