TDK conference 2018

Throughout the past decade the thoroughbred industry has become one of the worlds most valuable enterprises. With economy and profit being the focal point, animals have been manipulated to provide investors with the highest return. It is no shock that when we challenge mother nature it is often accompanied by consequences. By setting January 1st as the universal birth date for all TB, this has fueled an artificially advanced breeding season. This may satisfy industry timelines, but little attention has been attributed to what may be the downfalls to breeding outside the physiologic season.Studs have perfected the art of inducing ovulation through the use of artificial light, but an extended photoperiod during gestation has been neglected. For mare’s subject to an induced cycle, the final 3 months of gestation lie between Nov-Jan when light hrs are approx. 7hr 30 min, as opposed to during the physiologic reproductive season of 16 hr. One of the side effects of this is prolonged gestation lengths and reduced foal birth weight.Since equine reproduction is centered around circadian rhythm and the activity of photodependent hormones, it is fair to assume, that these hormones must also play a role during gestation and not only ovulatory peaks. Therefore, our aim for this research is to investigate, what hormones influencing the in-vitro development of the foal may too, be photosensitive and what environment must we provide for these mares during gestation.

70 TB mares were chosen and divided equally into a control and treatment group. 35 mares were exposed to a 16hr daylight regime for various durations prior to parturition. Each stable was fitted with an “Equilume stable light luminaire”. This contained a dim up/down feature at dawn and dusk, while also switching to a red light at night for the programmed hours of darkness to permit the nightly rise in melatonin, stabilising circadian rhythms while facilitating monitoring. Gestation lengths and time of foaling for each mare were recorded. Within 12hrs, a hair sample was pulled from the shoulder of each mare (also sampled 1 day prior to light exposure) and foal, FBW was measured and a heparinised blood sample was collected from each. Colostrum was collected immediately after parturition.Our preliminary results prove that light exposure of 35-45d prior to foaling optimize gestation lengths, FBW and colostrum quality. Mares subject to this photoperiod had a mean gestation length of 357.5 days, FBW 57.3kg, and colostrum SG 25.8ug. In the control group, the values were 370.6d, 54.71kg and 23.55ug, respectively. We suspect the hormone responsible for the increased FBW is IGF-1, this will be investigated using ELISA. The IgG value of all colostrum samples will also be analysed. Blue light has been proven to enhance coat shedding through stimulation of the photosensitive hormone PRL, we hope to explore whether this hormone has a transplacental affect by measuring PRL receptors in the foals and hair analysis.