Altrenogest treatment reduces the stress response of three-year-old warmblood mares during their initial equestrian training.

Horse mares are frequently treated with the progestin altrenogest with the aim to suppress estrous behavior and its negative impact on equestrian performance. Progestogens, however, also have sedative effects in males, and females of different species. The aim of our study was therefore to investigate altrenogest-induced changes in the stress response of female horses during initial equestrian training. Three-yr-old Warmblood mares were randomly assigned to treatment with altrenogest (ALT; 0.044 mg/kg once daily; n = 6) or sunflower oil (CON; n = 5) for 12 wk during training. At predefined steps of the training program (free movement, lunging without and with side reins, lunging with saddle, mounting of a rider, free riding, riding by an unfamiliar rider) salivary cortisol concentration, and heart rate were determined from 60 min before to 120 min after training. The same procedures were performed during repeated gynecologic examinations and 2 novel object tests. Bodyweight and body condition scores (BCS) were assessed at 4-wk intervals. During all training units, salivary cortisol concentration and heart rate increased (P < 0.001), but the increase was smaller in group ALT mares (time x treatment P < 0.001). Gynecologic examinations and novel object tests induced a much smaller increase in cortisol and heart rate (P < 0.001) than equestrian training with no difference between groups ALT and CON. Initially, bodyweight, and BCS decreased during training. The subsequent increase was larger in group ALT vs CON (time x treatment P < 0.05). In conclusion, altrenogest reduced the stress response of 3-yr-old mares to equestrian training. The use of altrenogest during equestrian competitions should therefore be reconsidered.

Development of Foals Until One Year of Age When the Dam was Exposed to Blue Monochromatic Light Directed at One Eye During Late Pregnancy.

In horses, blue LED light directed at one eye of pregnant mares shortens gestation length and results in the birth of foals with lower wither heights, similar weight and reduced hair length compared to controls. In this study, we have therefore analysed postnatal development of foals born to either blue LED light-treated (n = 20) or control mares (n = 20). Size, weight and hair coat changes were determined for 1 year and heart rate, heart rate variability (HRV) and selected haematology parameters for 1 month. Haematocrit decreased (P < .001) and leukocyte and lymphocyte counts increased (P < .001) but none of the parameters differed between groups. Heart rate (P < .001) and HRV (P < .01) increased until day 6 but did not differ between groups, indicating that foals born to blue LED light-treated mares were mature and healthy. The guard hair was shorter in foals born to treated mares compared to control foals at birth (P < .001) but no differences in hair coat length were observed beyond the age of 2 months. At birth and 6 days thereafter, wither height (P < .01) and elbow to carpus distance (P < .05) of control foals were increased relative to foals born to blue LED light-treated mares. Height differences decreased over time and and for elbow-to-carpus distance there was a time x group interaction (P < .005) In conclusion, blue LED light treatment of pregnant mares is without detrimental effects on postnatal foal growth and development.