Effects of ovarian structures identified at Ovsynch™ enrolment, disease history and lactation variables on odds of pregnancy to a fixed‐time artificial insemination after Ovsynch™. Issue 4 (April 2017) - Ingenhoff, L
Abstract : Objective: To determine the effects of ovarian structures present at Ovsynch™ enrolment, disease history, lactation variables and times bred on pregnancy per fixed‐time artificial insemination (FTAI) following fixed‐time insemination after Ovsynch and to determine the relationship between the size of ovarian follicular structures and concurrent presence of a corpus luteum (CL). Methods: The study was conducted in a 3000‐cow Holstein dairy herd. Over a 6‐month period, 886 non‐pregnant cows were examined by transrectal ultrasound and enrolled into 1132 Ovsynch events. Enrolled cows were synchronised using an Ovsynch‐56 protocol. At enrolment, both ovaries were scanned by transrectal ultrasound to identify and record the presence and size of ovarian structures. Cows that did not return to oestrus were pregnancy tested 32–38 days post‐insemination. Univariable and multivariable generalised linear mixed models (GLMMs) were used to determine the effect of each variable on pregnancy per FTAI. A univariable GLMM was also used to analyse the relationship between size of the dominant follicular structure and concurrent presence of a CL. Results: CL size (P = 0.039) and presence of a luteal cyst (P = 0.002) at Ovsynch enrolment significantly increased the odds of pregnancy. Occurrence of lameness (P = 0.035) or mastitis (P = 0.008) between calving and enrolment significantly decreased the odds of pregnancy. Neither the presence nor size of a follicular structure significantly affected the odds of pregnancy, although cows with larger follicular structures were less likely to have a concurrent CL (P < 0.001). Conclusion: Presence of luteal tissue at Ovsynch enrolment and recent disease events affected pregnancy per FTAI in cows inseminated after Ovsynch.