Effects of Thermal Stress on Reproductive Function
In the mare, a significant decrease in the number of embryos collected and a lower average embryo quality was observed when mares were used in moderate exercise which was sufficient to raise the body temperature by just a few degrees (°C). An ongoing study demonstrated little change in preovulatory follicle size or interovulatory interval in mares in a similar exercise regimen and analyses of the effect on reproductive hormones was completed in 2010.
Also, effect of exercise-induced thermal stress on the stallion was studied with placement of a thermal sensor in the scrotum and subsequent evaluation of semen parameters and endocrine profile. The primary finding is that moderate and even heavy workloads during extreme heat do not seem to influence sperm quality.
Influences of Body Condition on Growth and Reproduction
Studies have shown that keeping mares in an excessively fleshy body condition does not increase their reproductive performance over that seen when they are in a more moderate condition. One study utilized a mathematical model to identify the daily digestible energy required to increase body condition in mares by one score. More recent research incorporated exercising horses into the model with preliminary results showing strong correlations between what the model predicts and actual changes in sedentary horses body fat percent, body condition score, and even weight.
As a follow-up to a previous study in which mares were maintained at different body conditions during gestation, adrenal function of their offspring during the subsequent (yearling) year showed no detrimental or beneficial effects.
The above research topics were researched by retired professor Dr. Martha Vogelsang. For more information please contact Chelsie Huseman at chelsiejo@email.tamu.edu.
Controlling Seasonal Breeding in Mares
Dr. Gary William’s project is designed to understand the fundamental mechanisms that control seasonal breeding in the mare and to develop practical pharmacological strategies for controlling this phenomenon. Studies include:
1) Use of subcutaneously-administered gonadotropin releasing hormone (GnRH) for 14-28 days to stimulate the development of a large ovarian follicle and ovulation for early breeding of non-cycling mares in February and March. Currently, we are searching for a method to allow convenient injection of a subcutaneous depot of GnRH that would elicit desired responses without the need for a surgically-applied implant or pump device.
2) Roles of the RF-amide, RFRP3 (also called gonadotropin-inhibiting hormone; RFRP3) and its antagonist (RF9) in regulating hormones that control reproductive seasonality.
Publications:
Pharmacologic application of native GnRH in the anovulatory mare By Thorson, J.F., C.C. Allen, M. Amstalden, and G.L. Williams.
Hypothalamic distribution, adenohypophyseal receptor expression, and ligand functionality of RF-amide-related peptide 3 in the mare during the breeding and non-breeding seasons By Thorson, J.F., L.D. Prezotto, R.C. Cardoso, S.M. Sharpton, J.F. Edwards, T.H. Welsh, Jr., P.K. Riggs, A. Caraty, M. Amstalden, and G.L. Williams.