Uterine clearance of non-antigenic markers (51Cr) in response to a bacterial challenge in mares potentially susceptible and resistant to chronic uterine infections.

The purpose of this study was to investigate the physical ability of the mare's uterus to eliminate non-antigenic 51Cr microspheres during an infectious challenge. Mares both potentially susceptible and resistant to chronic uterine infections were used in this study. The procedure described serves as a model of the uterine capacity to clear physically infectious agents and inflammatory products during the acute phase of an infection. Based on the results from intra-uterine bacterial challenges, reproductive history, examination per rectum and endometrial biopsies, mares were classified as potentially susceptible (n = 6) or resistant (n = 5) to chronic uterine infections. On the third day of oestrus the mares were infused with Streptococcus zooepidemicus followed immediately by an inoculation of 51Cr labelled microspheres into the uterus. At 24 h post infection the uterus was lavaged to recover remaining microspheres. The procedure was repeated during the next 2 cycles to determine the retention of microspheres at 48 and 96 h post infection. Mares classified as potentially susceptible to chronic uterine infections demonstrated a significant delay in physical clearance of microspheres from the uterus compared to the resistant mares (P less than 0.0001). Uterine retention of microspheres in mares classified as potentially resistant was insignificant 24 h post inoculation. In contrast, mares classified as potentially susceptible to chronic uterine infections failed to clear microspheres from the uterus before 96 h post inoculation. It is concluded from this study that the physical ability of the uterus to clear infectious agents and inflammatory products may be a critical factor as a first line of defence against uterine infections.