Definition: Failure to expel the foetal membranes within 12 to 24 h after calving.
Incidence: Varies from 4.0-16.1%, but can be much higher in problem herds.
The key element in the pathogenesis of retained placenta in cattle is a failure of timely breakdown of the cotyledon-caruncle attachment after delivering the calf.
Mechanism of normal placental separation
Maternal immunological recognition of foetal MHC class I proteins expressed by trophoblast cells triggers an immune/inflammatory response that contributes to placental separation at parturition.
Mechanism of placental retention
Chemotactic factor for leukocytes is found in placentomes of cows with normal placental separation. It is absent in placentomes from cows with retained placentas. Blood leukocytes and neutrophils of cows with retained placenta are less reactive to chemotactic stimuli than in cows with normal placental separation.
Research presented by LeBlanc et al. (2004) points out that cows with a greater degree of negative energy balance prepartum and higher non-esterified fatty acid (NEFA) concentrations were 80% more likely to suffer from retained placenta. Similarly these authors found higher risk for retained foetal membranes in cows with lower circulating vitamin E concentration.
The recent data indicate that lack of uterine motility plays little or no role in the occurrence of retained placenta. Moreover cows with retained placenta have normal or increased uterine activity in the days after calving (Frazer 2005).
Delayed placental separation predisposes cows to acute puerperium metritis and endometritis post partum through:
For more details see The influence of placental retention on uterine health
See Therapy of retained placenta for details on treatment of the condition.
Examples of retained placenta in post partum cows