Abstract
The effects of exogenous equine somatotropin (eST) administration on ovarian activity and plasma hormone levels were evaluated on horse and pony mares. The objectives of this study were to determine the effects of eST on follicular development and circulating concentrations of leutinizing hormone (LH), estradiol, progesterone, and insulin-like growth factor I (IGF-I) in cyclic horse and pony mares. Sixteen mares received daily injections (im) of eST at a concentration of 25 μg/kg body weight on either Days 6 through 12 (Treatment A) or 13 through 19 (Treatment B) postovulation. In addition, contemporary mares were similarly given the carrier vehicle and served as controls (Treatments C and D). Blood samples were collected at 24-hr intervals and ultrasonographic evaluations were performed on the ovaries of each mare at 48-hr intervals beginning on the first day of treatment and ending either on the day of ovulation or 5 d postovulation. Circulating levels of insulin-like growth factor-I (IGF-I) were increased in treated mares by Day 3 post-treatment (P < 0.05). Also, mares in Treatment B exhibited a decrease in plasma estradiol concentrations (P < 0.05) when compared with control mares on Days 1 through 5 postovulation of the post-treated estrous cycle. In addition, circulating leutinizing hormone levels were different for mares in Treatment A compared with controls on Days −8 through −1 pre-ovulation (P < 0.05). All follicles present on the ovaries of each mare were measured and placed into one of five categories based on their diameter. Neither the mean number of follicles per size category ⩾8 mm in diameter nor the mean follicular diameter within each size category differed among treatment and control mares. However, eST treatment significantly increased the number of follicles ⩽7 mm on the ovaries of mares treated early in the estrous cycle when compared with control mares on Days 3 and 7 post-treatment and at the onset of standing estrus.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
