The inter-ovarian distribution of dominant follicles is influenced by the location of the corpus luteum of pregnancy

Abstract

The objective was to characterise the distribution of dominant ovarian follicles in the early post-partum period in relation to the side of the preceding pregnancy and its relationship with the left and right ovaries. Primiparous cows were enrolled over a 2-year period (n = 33 in Year 1 and n = 28 in Year 2). Ovarian follicles were observed daily by trans-rectal ultrasonography commencing within 9 days of calving. Dominant follicles (DF) were described as occurring on the ovary ipsilateral to the CL of preceding pregnancy (ipsilateral ovary of pregnancy, IOP) or contralateral to the CL of the preceding pregnancy (contralateral ovary of pregnancy, COP), and as occurring on the left or right ovary. Results in Year 1 were analysed for the effect of breed (Friesian n = 15; Jersey n = 18). There was a bias towards the COP for the first DF post-partum in both breeds (DF1; 70%; p<0.05). A breed interaction was observed with the second DF post-partum with a bias towards the COP in the Friesian (93%; p<0.05); but not the Jersey animals (50%). In Year 2, all cows were Friesians, and there was again a biased distribution of the DF1 towards the COP (89%; p<0.05) and for the combined distribution of the first three DF post-partum (76%; p<0.05) as well as the first ovulatory follicle (71%; p<0.05). A comparison of the pooled data for the location of the DF1 from both years showed that only one DF1 was observed on a left ovary in the 29 cases where the preceding pregnancy was also on the left side. This study demonstrated a bias in the distribution of DL in the early post-partum period towards the ovary on the side opposite that of the preceding pregnancy as well as towards the right side.