Abstract #M250

# M250
The effects of ovulatory status of the dominant follicle and spatial relationship of the corpus luteum on diameter and average growth rate of that dominant follicle.
Ashleigh M. Muth-Spurlock*1, Garrett F. Cline1, Caleb O. Lemley1, Jamie E. Larson1, 1Mississippi State University, Mississippi State, MS.

The aim of this study was to investigate the effects of ovulatory status of the dominant follicle (whether the follicle eventually ovulated or not) and spatial relationship of the corpus luteum (CL; contralateral or ipsilateral to the dominant follicle) on the diameter and average growth rate of that dominant follicle. Sixteen non-pregnant, multiparous beef cows were observed daily for estrus. Cows were randomly assigned to 1 of 2 treatments, daily ultrasound of: (1) the dominant anovulatory (AN) follicle (1st follicular wave), or (2) the ovulatory (OV) follicle (2nd or 3rd follicular wave). Ultrasonography exams were initiated on d 1 (AN treatment group) or on d 7 (OV treatment group) of the estrous cycle. Exams ended after 5 d of follicular dominance. Follicle diameter and whether the CL was ipsilateral or contralateral to the dominant follicle were recorded. The MIXED procedure of SAS was used for data analysis, with d of dominance (0 to 4) as a repeated measure; LSMeans and pooled SEM are reported. There was a treatment × spatial relationship interaction (P = 0.056) when evaluating average growth rate of the dominant follicle. Anovulatory follicles contralateral to the CL grew faster (1.137 ± 0.045 mm/d) than both ovulatory follicles contralateral to the CL (0.954 ± 0.036 mm/d) or ovulatory follicles ipsilateral to the CL (0.996 ± 0.029 mm/d). However, average growth rate of the dominant follicle was less (P = 0.041) in cows in the OV group compared with cows in the AN group (0.975 ± 0.023 and 1.07 ± 0.040 mm/d, respectively). When evaluating diameter of the dominant follicle over the 5 d of dominance, treatment, spatial relationship of the CL, d of dominance, and treatment × spatial relationship all affected diameter of the dominant follicle. However, when only evaluating the last d of dominance, these parameters did not significantly affect diameter of the dominant follicle. In conclusion, additional research is necessary to understand the interactions between future ovulatory status of a dominant follicle and spatial relationship of the CL.

Key Words: corpus luteum, follicle diameter, follicle growth rate