Rapid phase adjustment of melatonin and core body temperature rhythms following a 6-h advance of the light/dark cycle in the horse

<p>Abstract</p> <p>Background</p> <p>Rapid displacement across multiple time zones results in a conflict between the new cycle of light and dark and the previously entrained program of the internal circadian clock, a phenomenon known as jet lag. In humans, jet lag is often characterized by malaise, appetite loss, fatigue, disturbed sleep and performance deficit, the consequences of which are of particular concern to athletes hoping to perform optimally at an international destination. As a species renowned for its capacity for athletic performance, the consequences of jet lag are also relevant for the horse. However, the duration and severity of jet lag related circadian disruption is presently unknown in this species. We investigated the rates of re-entrainment of serum melatonin and core body temperature (BT) rhythms following an abrupt 6-h phase advance of the LD cycle in the horse.</p> <p>Methods</p> <p>Six healthy, 2 yr old mares entrained to a 12 h light/12 h dark (LD 12:12) natural photoperiod were housed in a light-proofed barn under a lighting schedule that mimicked the external LD cycle. Following baseline sampling on Day 0, an advance shift of the LD cycle was accomplished by ending the subsequent dark period 6 h early. Blood sampling for serum melatonin analysis and BT readings were taken at 3-h intervals for 24 h on alternate days for 11 days. Disturbances to the subsequent melatonin and BT 24-h rhythms were assessed using repeated measures ANOVA and analysis of Cosine curve fitting parameters.</p> <p>Results</p> <p>We demonstrate that the equine melatonin rhythm re-entrains rapidly to a 6-h phase advance of an LD12:12 photocycle. The phase shift in melatonin was fully complete on the first day of the new schedule and rhythm phase and waveform were stable thereafter. In comparison, the advance in the BT rhythm was achieved by the third day, however BT rhythm waveform, especially its mesor, was altered for many days following the LD shift.</p> <p>Conclusion</p> <p>Aside from the temperature rhythm disruption, rapid resynchronization of the melatonin rhythm suggests that the central circadian pacemaker of the horse may possess a particularly robust entrainment response. The consequences for athletic performance remain unknown.</p

Oral and injectable synthetic progestagens effectively manipulate the estrous cycle in the Przewalski’s horse (Equus ferus przewalskii)

To date, there has been limited research on manipulation of the estrous cycle in endangered equids. The objectives of this study were to assess the efficacy of using combinations of: (a) oral altrenogest and PGF(2)alpha, and (b) injectable altrenogest and PGF(2)alpha for manipulation of ovarian activity in Przewalski's mares. Reproductive cycles were monitored by assessing follicular changes with rectal ultrasound and changes in urinary steroid hormones. In Study 1, five cycling mares were treated with oral altrenogest (n = 11 cycles) for 14 days. In Study 2, cycling mares were treated with oral altrenogest for 12 days (n = 5 cycles; n = 5 mares) or a single injection of biorelease altrenogest (n = 10 cycles; n = 6 mares). In all study groups, PGF(2)alpha was given 2 days before cessation of progestagen treatment. In Study 1, mares responded in six of 11 cycles (54%) where treatment occurred with normal ovarian follicular development post hormone therapy. In Study 2, mares responded in four of five (80%, oral altrenogest) and eight of 10 (80%, injectable altrenogest) cycles with the development of an ovulatory follicle. With the use of injectable altrenogest, there was an obvious suppression of urinary estrogens and progetsagens. These results indicate that manipulation of the estrous cycle of Przewalski's mares can be achieved by administering oral (12 days) or injectable form of altrenogest in conjunction with PGF(2)alpha. Findings in the present study may have long term application for the development of timed artificial insemination as a genetic management tool for this critically endangered equid. (C) 2014 Elsevier B.V. All rights reserved