Sperm contact time in uterus and endometrial inflammation in mares bred by transrectally guided deep horn artificial insemination

Sperm elicit an acute uterine inflammatory reaction that resolves within 24 - 48 hours in normal mares. Delay in uterine clearance results in persistent inflammation, alters uterine environment, and decreases embryo survival, resulting in substantial economic losses. To improve embryo survival, uterus is lavaged within the first 4 - 12 hours after insemination. Substantial reduction in pregnancy rate was observed if lavage is performed prior to 4 hours. Deep (uterine) horn transrectally guided artificial insemination (DHAI) is a technique that places sperm close to utero-tubal junction, ipsilateral to the ovulation side. Advantages of DHAI are reduction in volume and/or number of sperm inseminated, and reduction in sperm transport time, with faster oviductal sperm colonization. Since severity of endometrial inflammation is directly related to number of sperm and duration of uterine-sperm interaction, we hypothesized that uterine lavage prior to conventional 4 hours would have an effect on uterine inflammation. Objectives were to determine degree of inflammation at 1 and 4 hours after insemination in mares bred by DHAI and determine pregnancy in mares lavaged earlier than 4 hours. Four warmblood and 3 Thoroughbred mares with normal reproductive histories were used over 14 estrous cycles in a cross-over experimental design. Mares with obvious uterine edema and a dominant preovulatory follicle were induced to ovulate with 1 mg of Deslorelin IM. Within 0 - 6 hours after ovulation, mares were bred by DHAI with 1 x 0.5 ml straw of frozen-thawed semen from 1 of 2 stallions of proven fertility and containing 120 - 160 x 10 6 total sperm. On the first estrous cycle, mares were randomly assigned for lavage at 1 or 4 hours following DHAI. Mares were rested for a cycle and assigned to opposite group. At lavage, mares were examined for presence and degree of endometrial edema. Presence of uterine fluid and effluent samples were analyzed for presence or absence of PMN’s, and PMN numbers. Pregnancy diagnosis was conducted at 12 - 14 days following DHAI. Uterine semen contact time of 4 hours versus 1 hour had a significant effect on degree of uterine edema (p < 0.046), presence or absence of PMNs (p < 0.0009), and PMN numbers (p < 0.0006), but not on amount of accumulated uterine fluid (p > 0.5) or pregnancy rate (p = 0.28). We concluded that presence of sperm in uterus of normal mare for 1 hour elicited lesser inflammatory reaction compared to 4 hours and pregnancy rate was not affected by early lavage in mares bred by DHAI.

Keywords: Endometritis, deep horn insemination, uterine lavage, pregnancy rate

This manuscript was originally published in the journal Clinical Theriogenology Vol 12(3) Sept 2020.  Clinical Theriogenology is the official journal of the Society for Theriogenology (SFT) and the American College of Theriogenologists (ACT).  This content has been reproduced on the IVIS website with the explicit permission of the SFT/ACT.