Diseases - Sheep

Abortion

Species

All. Cattle are the main species of interest.

Description

Abortion is the early termination of pregnancy with expulsion of a dead foetus. A dead full term foetus is referred to as a still birth rather than an abortion. The normal gestation period for a bovine is 9 months. The gestational age of an aborted foetus can be estimated by measuring the distance in inches from the crown of the head to the tail head of the rump (inches=cm/2.5). This distance is multiplied by 2. The square root of this product gives the approximate gestational age in months.

Abortions may occur days, weeks or months after exposure to an infectious microorganism, toxin, stress or genetic fault that impacts the foetus or placenta. This means abortions may be the result of factors occurring before animals entered the export process. Abortions in up to 3% of breeders per year are considered normal.

Aborting animals may have higher risk of retained foetal membranes and uterine infection (metritis) if aborting after 3mo of pregnancy, and development of the mammary gland may lead to mastitis.

Heat stress, mouldy feed, bovine virus diarrhoea virus and neosporosis are some of the agents potentially increasing abortion rates above background levels in the live export process. Fever, severe trauma and administration of glucocorticoid drugs (such as Dexafort™, Dexadresson™) may cause abortion in individual animals. The sedative xylazine, used for minor surgical procedures at sea, may cause abortion in near term pregnancies.

Infectious diseases known to cause abortion and worth considering in investigation of outbreaks include: trichomoniasis, campylobacter, bluetongue virus, akabane virus, salmonella, mycoplasma, Histophilus somni, leptospirosis, brucella, chlamydophila, listeria, neospora, infectious bovine rhinotracheitis and bovine virus diarrhoea virus. Non-infectious causes included plant poisonings and possibly heat stress.

There are three conditions occurring at sea that are sometimes mistaken for evidence abortion has occurred. First, mammary gland development and premature lactation occur commonly in heifers and cows (both pregnant and non-pregnant), without abortion or calving having occurred. Second, bloody vaginal discharges occur commonly 2-3 days after oestrus. Third, coccidiosis in adult cattle at sea is common - these animals strain, have a raised tail and may have bloody faeces staining the tail and perineum.

Clinical Signs and Diagnosis

Signs of abortion include: straining, raised tail, red to brown coloured vaginal discharge, protrusion of foetal membranes, mammary gland development, and the discovery of a foetus or foetal membranes in a pen. Rectal and vaginal examination of animals may be required to confirm abortion.

Specimens for laboratory diagnosis ideally include acute and convalescent maternal sera and the complete fresh (or frozen) foetal-placental unit. Otherwise submit sections of foetal and placental tissues in formalin plus foetal stomach contents for microbiology.

Treatment

Treatment is usually not required unless assistance to remove the foetus is necessary in which case antibiotics (procaine penicillin, oxytetracycline, or trimethoprim sulpha) may be recommended. Retained foetal membranes should be cut off level with the vulva and parenteral antibiotics (oxytetracycline, or trimethoprim sulpha) administered. Antibiotic pessaries are not effective at combating intra-uterine infection and are not recommended.

Prevention

Minimise stress, especially heat stress; avoid mouldy feeds; practise low stress handling and transport methods; don't administer glucocorticosteroids; protect feed from contamination; cull persistently viraemic pestivirus animals.

Syndromes