US Doppler in the monitoring of hemodynamic alterations of the supplementary corpus luteum in cyclic mares

Abstract

For the success of an equine breeding program, follow-up by a veterinarian is essential. In early pregnancy, luteinized follicles develop into an accessory or supplementary corpus luteum (SCL) which, like the primary corpus luteum, produces progesterone and contributes to the maintenance of early pregnancy (Hannan et al. Domestic Animal Endocrinology. 2020; 72:106424). If SCLs are insufficient, progesterone supplementation may be required but research data in this field are limited. Hence it is important to monitor the hemodynamic changes of the SCLs using Doppler ultrasonography (US Doppler). The aim of this study was to follow the onset and development of SCLs, evaluate their degrees of vascularization, subjectively (determining vascularity) and objectively (comparing the number and intensity of pixels). Crossbred mares (n=15) were inseminated, then SCLs monitored in Rio de Janeiro, Brazil. There was an average of 2.8 SCL/mare due to the ovulation and development of SCLs and differences in vascular perfusionwere seen between days 35 and 70 of gestation. There was a correlation (P<0.001) between SCL vascularization and the number and intensity of pixels, with the greatest increase occurring between days 70 and 119 of pregnancy. This corresponds with the peak production of progesterone by these structures. From day 120, a decrease in the vascular perfusion of the SCLs was seen, and at 140 days of gestation, the few SCLs that remained were in regression. This is logical because by this stage of gestation, progesterone is mainly of placental origin. Thus, US Doppler evaluation of SCLs in early pregnancy may assist in the decision whether to administer supplementary progesterone and for how long or not at all. Future research that may evaluate the contribution of equine chorionic gonadotropin to the formation of SCLs, its effect on the plasma concentration of progesterone as well as any requirement for progesterone supplementation at all is required.