Effect of abnormal vaginal discharge at oestrus on conception rate after artificial insemination in cows

During a 2-year study from January 1997 to December 1999, the visual characteristics of the cervical mucous discharge of cows and heifers in oestrus and their relations to conception rate were studied in a large dairy herd of Holstein-Friesian cows. Cows were divided into two groups based on mucous discharge being of normal or abnormal appearance and the group with abnormal discharge was further divided into the following classes: cervical mucus with urine (CMU), cervical mucus with microbes (CMM), cervical mucus with blood (CMB) and a group with no cervical mucus (NCM). From 6169 cases of cows in oestrus, 82·2% had normal discharge, and the remaining 17·8% had abnormal discharge classifications (6·1% CMU, 5·1% CMM, 0·5% CMB and 6·1% NCM). Conception rate after artificial insemination (AI) in the normal group (38·3%) was significantly higher than that of the abnormal group (27·9%), ( P P P > 0·05). From 1734 cases of heifers in oestrus, only 6% had abnormal discharges, and the conception rates of the normal and abnormal groups were not significantly different ( P > 0·05). We conclude that AI of cows in oestrus discharging cervical mucus that is contaminated with urine, microbes or blood produces conception rates significantly lower than those of cows discharging a normal and clear mucus. Absence of a cervical mucous discharge at the time of AI of cows does not imply a low conception rate. In the case of heifers, appearance of cervical mucus had no effect on the conception rate after AI.