The literature on the effects and causes of retained placenta in the cow is reviewed. On a herd basis the condition can adversely affect milk yield and fertility, but on an individual cow basis the effects are unpredictable. The aetiology of retained placenta has been extensively studied and many causal factors have been implicated, but little is known of how many of them cause the condition. As a result its prevention and prediction is uncertain, primarily because of the lack of knowledge of the normal process of placental release. Vascular changes and uterine contractions play a role in placental release, but current opinion suggests that the primary cause of retained placenta is the retention of the feto-maternal union. Release only occurs after a process of maturation, which involves hormonal and structural changes. The factors which are thought to influence these changes, and thus cause the condition, are discussed.
The wide range of results suggests that more needs to be done to disseminate up-to-date knowledge of pain in cattle to veterinarians to ensure they provide appropriate levels of analgesia. In particular, the baseline data from this study can be used by practitioners to identify whether they are underestimating pain in cattle and, if they are, to assess whether they are using analgesia appropriately. Additionally, this dataset provides an informed and independent assessment of the pain associated with husbandry procedures, and could be used to better guide legislation concerning pain control of such procedures.
The literature on the treatment of retained placenta and its effects is reviewed. Manual removal, the oldest and commonest method of treatment, benefits parlour hygiene but may adversely affect the cow. The use of collagenase may allow manual removal without such side effects. Ecbolic drugs are often ineffective, both as prophylaxis and treatment for the condition. They are most effective within one hour of parturition, particularly after a caesarean section in which tocolytic drugs have been used. Endometritis is a very common sequel to retained placenta. Antibiotics and oestrogens have been used to treat, control or prevent the condition, but they are not routinely effective and may have deleterious side effects. Gonadotrophin releasing hormone and/or prostaglandins have been used to reduce the deleterious effect of retained placenta on fertility, but the results obtained have been inconsistent.
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