Effects of assisted calving on reproductive efficiency in dairy cows without retained placenta

This study evaluated the effects of assisted calving on the occurrence of retained placenta (RP) and reproductive efficiency, as well as the effects of assisted calving on the reproductive efficiency of dairy cows without RP. Calvings were classified as normal (single live calf), assisted (human intervention required, single live calf), abortion, stillbirth, or twin. The interval from calving to first artificial insemination (AI), conception rate at first AI, and days open were analyzed. Statistical analyses were performed using analysis of variance and chi-square tests with R Core Team software. In total, 6,808 calvings were analyzed: 85.56 % normal, 4.36 % assisted, 4.77 % abortions, 3.44 % stillbirths, and 1.87 % twin calvings. Calving type affected the occurrence of RP (P = 0.0001). Cows with assisted calving had longer days open (151.00 ± 101.70 days; P = 0.004) than did cows with normal calving (124.08 ± 87.56 days), as well as a tendency toward a longer interval from calving to first AI (P = 0.093). A subgroup of 2,422 cows without RP was analyzed. Cows with assisted calving and without RP had longer days open (144.00 ± 102.60 days; P = 0.035) than did cows with normal calving (123.23 ± 87.18 days). No effect of assisted calving was detected on the interval from calving to first AI or on conception rate at first AI. It is concluded that assisted calving is associated with a higher incidence of RP, and that calving assistance negatively affects the reproductive efficiency of dairy cows, regardless of RP occurrence.

Keywords:
cattle; reproductive performance; dystocia; days open.