Common Causes Of Cattle Abortion In New Zealand

Common Causes Of Cattle Abortion In New Zealand
Pregnancy loss should be under 5%; levels above this or clusters of abortions should be investigated with an aim of preventing future losses. Diagnosis from samples is difficult as we are looking at the result of an infection or incident which could have happened some time ago, and so only around 35% of laboratory investigations yield a definitive diagnosis. This result can be higher if a full range of fresh samples are available; this means maternal and foetal blood; stomach contents, spleen, liver and lungs from the aborted foetus and fresh placenta. If the aborted calf is small enough we usually send the whole calf.

Bacterial Abortion

The causes of bacterial abortion include:
1.Brucellosis - a highly contagious disease and a serious zoonosis. This disease has been officially eradicated from New Zealand but the situation is closely monitored by the laboratories.
2. Leptospirosis – this is caused by several different strains resulting in sick cows, milk drop, abortions, weak calves, anaemia and jaundice. Lepto is less common now due to widespread vaccination programs but is still a risk where cattle are in contact with pigs or herds are unvaccinated. Infected cows shed high numbers of Leptospira in urine and so the disease is highly infectious. Abortion normally occurs 4-12 weeks after infection so it can be difficult to diagnose. Leptospirosis is also a significant zoonotic disease.
3. Campylobacterosis – is a very rare venereal disease of cattle that can cause abortion.
4. Salmonella - abortion due to salmonella is confined to areas of the South Island where cattle have contact with infected sheep.
5. Listeriosis - causes sporadic or small clusters of abortions, usually in late pregnancy. It is always associated with feeding silage that has been contaminated with soil, has low dry matter and has undergone incomplete fermentation.
6. Bacillus Licheniformis - is a bacteria associated with feeding mouldy silage, or other mouldy feedstuffs. Abortion usually occurs in late pregnancy with the infection causing the placenta to become necrotic resulting in separation and abortion.

Viral Abortion

1. IBR – worldwide, IBR causes widespread abortion problems but in New Zealand it only causes respiratory disease.
2. BVD – is one of the most significant causes of bovine abortion in New Zealand. BVD causes infertility, abortion, weak calves and congenital defects, and can potentiate the effects of other abortion agents such as Neospora (see below). The pattern of disease depends on the stage of pregnancy when the infection first occurred and the previous disease exposure. Persistently Infected (PI) animals are often the source of infection, and controlling the disease involves removal of PIs as well as robust vaccination programs. Breeding bulls should always be tested for BVD and vaccinated.

Protozoal Abortion

Neosporosis – is one of the most commonly diagnosed causes of abortion worldwide. Cattle become infected by consuming food and water contaminated with Neospora in dog faeces. Dogs become infected by eating abortion material or infected cow meat, however there is also significant transmission from mother to calf in the uterus. These heifer calves are at greater risk of aborting to their first pregnancy. These congenitally infected heifers will be permanently infected for the rest of their life and are at a higher risk of aborting at each pregnancy. Abortion can occur at any stage but it is most common at five to six months. Neospora is also associated with stillborn and weak calves. Treatment and control is difficult as the exact lifecycle and spread is not fully understood. Many herds will be endemically infected and suffer chronic higher abortion rates than normal. When it occurs simultaneously with BVD, the immune-suppressive effects of BVD can cause a more severe Neospora outbreak.

Fungal Abortion

1.Aspergillus - this infection is associated with feeding of mouldy hay or silage. Fungal abortions usually occur between May and July, usually in late pregnancy. The incubation period varies from several weeks to several months and requires exposure to large amounts of contaminated feed. There are no other clinical signs in cows that abort to aspergillus.
2.Mortierella - is similar to Aspergillus except cows that abort due to Mortierella go on to develop a fatal mycotic pneumonia as the fungal infection spreads from the uterus to the lungs.

Date Added: Tuesday, 28th June 2016