Retention of fetal membranes, or retained placenta, in cows usually is defined as failure to expel fetal membranes within 24 hours after parturition. Normally, expulsion occurs within 3–8 hours after calf delivery.
Etiology of Retained Fetal Membranes in Cows
Normal placental expulsion involves a variety of cell types, including neutrophils, T cells, and macrophages. Retention of fetal membranes is, in part, mediated by impaired migration of neutrophils to the placental interface in the periparturient period. Additionally, proinflammatory macrophage populations are decreased in the caruncular tissue of cows with retained placenta, potentially leading to decreased collagenolysis and fibrinolysis at the cotyledonary-caruncular interface. Uterine contractility is increased in affected cows, and lack of placental detachment, rather than insufficient uterine motility, is responsible for retention of fetal membranes. Cows with retained fetal membranes have increased cortisol and decreased estradiol concentrations in late pregnancy, which further impacts immune function in affected cows by exerting local and systemic immunosuppressive effects. Uncomplicated retention of fetal membranes is unsightly and inconvenient for animal handlers and milkers but generally not directly harmful to the cow.
Epidemiology of Retained Fetal Membranes in Cows
Retained fetal membranes were identified by producers as a health problem in 4.5% of the dairy cow inventory in the most recent (2014) USDA National Animal Health Monitoring System survey. Incidence is lower in beef cows than in dairy cows. Risk factors include abortion (particularly with brucellosis or mycotic abortion), dystocia, twin birth, stillbirth, hypocalcemia, high environmental temperature, advancing age of the cow, premature birth or induction of parturition, placentitis, and nutritional disturbances, including increased prepartum serum concentrations of nonesterified fatty acids. Cows with retained fetal membranes are at increased risk of metritis, displaced abomasum, mastitis, ketosis, and early-lactation culling. Cows may experience negative impacts on fertility in the subsequent lactation. Economic cost of a case of metritis is estimated at $386 (USD) per case, attributable to decreased milk yield, increased time to next pregnancy, increased risk of associated periparturient diseases, and increased culling risk.
Clinical Findings of Retained Fetal Membranes in Cows
Retained fetal membranes are characterized by varying amounts of degenerating, discolored, ultimately fetid membranes protruding from the vulva for >24 hours after parturition. Occasionally, the retained membranes may remain within the uterus and not be readily apparent, in which case their presence may be signaled by a foul-smelling discharge. In most cases, there are no clinical signs of systemic illness. When systemic clinical signs are present, they are related to toxemia.
Diagnosis of Retained Fetal Membranes in Cows
Diagnosis is usually straightforward based on history and clinical signs of the fetal membranes protruding from the vulva. Membranes retained within the uterus or projecting into the cervix or vagina can be detected on vaginal examination.
Treatment of Retained Fetal Membranes in Cows
Manual removal of the retained membranes is not recommended and is potentially harmful. Trimming of excess tissue that is objectionable to animal handlers and contributes to gross contamination of the genital tract is permissible. Untreated cows expel the membranes in 2–11 days.
Routine use of intrauterine antimicrobials has not been found to be beneficial and may be detrimental. Although advocated at various times, oxytocin, estradiol, prostaglandin F2alpha, and oral calcium preparations have not been shown to hasten expulsion of retained membranes or to prevent complications. When systemic clinical signs of illness are present, systemic treatment with antimicrobials is indicated.
In herds in which incidence of retained fetal membranes is unacceptably high, predisposing causes should be sought and eliminated. Supplementation with vitamin E and selenium for herds in which these nutrients are deficient has been found to be beneficial.