Protocol modification for frozen semen insemination in mares

Abstract

Equine breeding commonly employs artificial insemination with increased demand for cryopreserved semen. Classic management strategies have relied on intensive mare examination, commonly with insemination after ovulation. Previous authors (Squires.et.al. AAEP Proc. 2003;49:353-356) looked to reduce examination frequency utilizing timed insemination. Examination frequency was reduced but a second insemination was used. In an effort to reduce examination frequency and eliminate a second insemination, a protocol modification was made in the timing of inseminations. Mares were part of active breeding programs associated with the practices of two theriogenologists. A total of 67 mares, ranging from 3-22 years of age, yielded 127 total cycles which were inseminated over 3 years. The horses represented a variety of breeds, and all mares were to carry their pregnancies. When transrectal palpation and ultrasound showed the mares had a dilated cervix, uterine edema and an ovarian follicle greater than 35mm in size, ovulation was induced. Induction was designated time 0 hours. Mares were induced with either hCG 3000IU IV, deslorelin acetate 1.7mg IM or histrelin 0.5mg IM. Mares were examined and inseminated according to the protocol chosen, 6 Hours, Timed or Proposed. The 6 Hour method used mare examinations every 6 hours until ovulation was detected and inseminated at that time. Timed used examinations at 24, 30 and 48 hours with insemination at 30 and 48 hours. Proposed used examinations at 24, 30, 33-36 and 48 hours, with insemination at the 33-36 hours. Examination at 48 hours was used to confirm ovulation and proper timing. Nine mares were inseminated on 13 cycles in the Proposed group. Thirty mares were inseminated on 38 cycles for the Timed group. 48 mares were inseminated on 76 cycles for the 6 Hours group. Pregnancy rates per cycle for each group were 69.2%, 44% and 48.6% respectively. Statistically there was no difference between the groups. We feel this demonstrates that the Proposed method is an acceptable method to achieve pregnancy per cycle rates that are comparable with previously described methods. Disadvantages of the study was its retrospective nature and the small sample size of the proposed method. Advantages were the removal of examinations between the hours of 10PM and 8AM and the use of a single dose of frozen semen. Adjusting the timing of ovulation induction to the morning eliminated overnight and early morning exams, which had a direct, positive effect on professional wellbeing which cannot be understated.