Abortion in dairy cattle is commonly defined as a loss of the foetus between the age of 42 days and approximately 260 days (buffaloes 300 days). It is important to differentiate non-infectious from infectious abortions. The prevalence of brucellosis (B. abortus) can have a disastrous effect on the pregnant herd with a high percentage of abortions.
Infectious agents are perhaps the most frequently thought of cause of bovine abortion. Bacteria which can cause abortion are Brucella, Leptospira, Haemophilus, Listeria, Ureaplasm, Mycoplasma. Viral infection which causes abortions are Bovine Viral Diarrhea virus (BVD) and Infectious Bovine Rhinotracheitis virus (IBR, BHV- 1). Protozoa causing venereal diseases and abortion are Campylobacter fetus ss. Venerealis, Trichomonas foetus and Neospora caninum. Late abortions are more likely to be seen with neosporosis, leptospirosis and Brucellosis. Earlier losses (often recognised only when cows are pregnancy-tested as empty) may be more likely to be due to pestivirus or vibriosis. Sporadic abortions may indicate that the herd is partly immune to the disease, and that the disease has been present for some time. Other toxic causes of abortions are silo gas, severe nitrate or prussic acid poisoning and toxic plants, mycotic infections, selenium and vitamin A and E and iodine deficiency. Uses of cortisone or prostaglandin in pregnant cows, injury, domestic pets spreading infectious agents among cattle, are some of the other causes of abortions. While brucellosis – which can be sporadic, enzootic or epizootic – is highly infectious and varies with such factors as climate, the extent of control measures, and nutritional state of the animal. In populations suffering from brucellosis the incidence of abortion can be higher than 10% of established pregnancies. The incidence of abortions however, is less than 2% in populations free of brucellosis. The role of the veterinarian is important to recognize each case of abortion in order to establish a correct diagnosis and undertake appropriate treatment.