Uterine Changes Associated with Repeated Inseminations and Embryo Collections in Mares

Embryo transfer has been established as a method to obtain additional offspring from valuable mares. However, repeated embryo collections can result in the establishment of chronic inflammation within the mare's uterus.

1. Introduction

Embryo transfer is being increasingly used in the equine industry. An embryo donor can be flushed at ~3-wk intervals for the collection of embryos. Six to 8 days after ovulation, the embryo is collected by flushing collection medium in and out of the uterus [1]. Objectives of the study were to determine if repeated inseminations and embryo collections result in inflammation or infection in the uterus and to determine if administration of estrogen during anestrus would reduce uterine inflammation or infection.

2. Materials and Methods

Light-horse mares (n = 21) were used for the study. Uterine evaluations, consisting of an ultrasound exam, uterine culture, uterine cytology, and uterine biopsy, were performed at (1) estrus before ovulation in spring of the first year, (2) after three embryo collection attempts, (3) after six embryo collection attempts, (4) in mid-winter, and (5) after the first ovulation of the spring of the second year. Uterine biopsies were evaluated for acute inflammation, chronic inflammation, and fibrosis; each uterine parameter was scored (1 = normal, 5 = severe changes). Prostaglandin was administered after each embryo collection attempt. Reproductive tracts were subsequently scanned until a follicle >35 mm and uterine edema were observed. At that time, the donors received human chorionic gonadotropin (hCG) to induce ovulation. Mares were inseminated with 500 x 106 progressively motile sperm the day after hCG administration, and embryo collections occurred 6 - 8 days after ovulation. For embryo collections, mares' uteri were lavaged with 4 l of a complete embryo flush medium. aIn the anovulatory season, mares were divided into an untreated, control group or treatment group that received estradiol-17β (3 mg, q 24 h, IM, for 6 days) with the treatment replicated four times. For statistical comparisons, analysis of variance (ANOVA) for repeated measures was used.

3. Results

Approximately seven embryo collections were attempted per donor during the breeding season, and an average of five embryos were collected per mare. Scores for culture, cytology, chronic inflammation (biopsy), and acute inflammation (biopsy) differed significantly by evaluation. The highest culture scores were obtained in the spring of the first year and before inseminations and embryo collections. Cytology scores, based on the number of inflammatory cells, were elevated only during the mid-winter examination, whereas acute inflammation in the biopsied endometrium was significantly lower at this evaluation. Fibrosis within uterine tissue did not change after repeated embryo collections. However, chronic inflammation significantly increased within the endometrium, as observed in biopsies, by the spring of the second year. Administration of estradiol did not affect uterine parameters over all evaluation periods; however, between the fall of year 1 and the spring of year 2, chronic inflammation significantly increased in non-treated mares but not in treated mares.

4. Discussion

In this study, repeated inseminations and embryo collections were associated with increased chronic inflammation; they were not associated with increased infectious organisms within the uterus. During insemination, a significant insult occurs to the uterus. If contamination is not overwhelming, the healthy uterus contends with the invasion through a series of events, resulting in an inflammatory reaction that helps to clear the uterus of sperm and contaminating debris [2]. With repeated inseminations and embryo collections, donor mares may be susceptible to the additive effects of repeated insults.

One-half of the mares assigned to the project were treated with estradiol during the winter months; the intent was that estrogen stimulation of the uterus during anestrus could help resolve infection or inflammation if it occurred after repeated uterine insults during the breeding season. In this study, inflammatory scores were not significantly elevated in the fall, and mare numbers were low. However, the results do suggest a beneficial effect of estrogen treatment, and additional research is being conducted.

Repeated inseminations and embryo collections resulted in increased chronic inflammation within the endometrium. Additional research is required to determine the long-term effects of chronic inflammation on uterine function and fertility.

Funding for this study was provided by the American Quarter Horse Association Foundation in Amarillo, TX.

Footnotes

1. ViGro complete flush, AB Technologies, Pullman, WA 99163.