Corpus luteum diameter and serum progesterone level, during the estrous cycle in colombian criollo mares

Objective. To determine the corpus luteum (CL) diameter and serum progesterone levels (P4) during the estrous cycle (EC) in Colombian Criollo mares (CC). Materials and methods. Thirty 4 to 14-years old mares were employed. The animals were located in Pereira (Colombia). Transrectal ultrasonography was performed daily through two EC, from ovulation (day zero) to the next ovulation. Blood samples were taken every 48 hours during one EC, to measure serum levels of P4 by radioimmunoassay (RIA). Data analysis was performed using descriptive statistics, with standard deviation, and student’s t-distribution to determine differences between the EC and a test of correlation between CL diameter and P4 levels. Results. The size of the CL during the EC was 18.3±5.9 mm (mean ± standard deviation). The average CL diameter found on day zero was 25.1±4.5 mm and the final size, was 8.5±0.9 mm on day 20 of the EC. The larger CL diameter was found on day 2 post-ovulation (26.4±5.0 mm). The highest serum P4 levels were found on day 6 post-ovulation (10.7±4.3 range from 2.51 to 18.8 ng/ml); during diestrus, they were 6.6±3.6 (range 1.15 to 10.7 ng/ml) and during estrus, 0.25±0.3 (range 0.01 to 0.86 ng/ml). Conclusions. The CC mare CL presents a dynamic similar to that reported in the literature. Present findings could be used as a starting point for the establishment of reference values of clinical importance.