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Know What Causes Abortions

Abortion can be one of the greatest losses to the cow-calf and purebred beef producer from fall onwards. There are a great number of causes for abortion. Unfortunately 24 to 50 per cent of these causes go undiagnosed.

Abortions may occur in the early stages of pregnancy and are revealed at preg-checking time as open cows. If a high percentage of open heifers or cows is found at this time your veterinarian may want to pursue various tests to identify the cause. If bull evaluation does not reveal any deficiencies then the cowherd becomes the focus.

Nutritional status of the herd is questioned as deficiencies of selenium, copper, vitamin A, phosphorus, and iodine can be responsible for open cows. Should the open cows go for slaughter the veterinarian may ask that the reproductive tracts of these cows be obtained, examined, and tested for certain infectious reproductive diseases.

It is important to realize that abortions stem from problems not only with the individual fetus, but with environmental and maternal problems also.

Because most aborted fetuses do not reveal any gross abnormalities, further diagnostic workup is required to identify the cause of death. Microscopic evaluation of fetal tissues and culturing of stomach contents are two such workup procedures. It is important that the aborted fetus be as fresh as possible. This can be vital to obtaining information.

Submission of the placenta doubles the chances of a diagnosis. Once again, it should be as fresh as possible. The fetus and the placenta should be placed in separate clean plastic bags and kept cool. If the cow still has some retained placenta it is best to pull out this portion ensuring it contains a cotyledon, snip it and submit it. Obtaining a diagnosis from aborted fetuses and placenta contaminated with soil, straw, and manure is truly a diagnostic challenge and often unrewarding.

An abortion rate of two to three per cent over the latter stages of pregnancy is considered normal. However, abortions which occur close together may be a concern. Watch closely around six months gestation for tell-tale signs of abortion such as a wet tail or retained placenta

If several abortions have occurred together your veterinarian will want to pursue several avenues in an attempt to diagnose the problem. A history detailing nutrition, vaccination protocol, introductions of new heifers or cows to the herd, and the environmental conditions are vital to understanding the nature of the problem.

The body condition of those cows and heifers that have aborted and their herd mates are evaluated. Aborted cows and their herd mates should have blood samples taken and one or two caruncles (uterine biopsies) may be taken from recently aborted cows.

The most common infectious causes of abortion in our region are IBR (Infectious Bovine Rhinotracheitis) and BVD (Bovine Viral Disease). IBR is a virus and causes abortions primarily in the last trimester (six to nine months). Even though exposure may have been months earlier, abortion usually does not occur until the sixth month of gestation. Calves carried to full term may be born weak.

The consequences of BVD infection depend on when contact is made with the fetus. If the fetus is exposed to the virus before 100 days of gestation, abortion and mummification are the consequences. If contact with the virus occurs in the middle third of the pregnancy, congenital abnormalities of the nervous system and eyes are evident. Contact in the last trimester of pregnancy generally results in normal healthy calves with titers against BVD or other times the fetus is born alive but persistently infected meaning it is shedding the BVD virus.

Other infectious causes of abortion include leptospirosis, vibriosis, neospora, listeriosis, brucellosis, and trichomoniasis. These are less common and methods to prevent these causes would be dealt with at the time of diagnosis. Now very accurate DNA tests on blood semen from bulls or manure can help pinpoint if infection is present.

It is pretty much standard for beef producers to vaccinate for the IBR and BVD viruses. Two types of products are available. A killed vaccine product is safe to give pregnant animals but requires two shots the first year and annual vaccination in subsequent years. The second, a modified live vaccine, gives better immunity than the killed vaccines, is less expensive and is best given just before the breeding season. If the BVD and IBR vaccine status is protective, cows can even be vaccinated in late pregnancy with most of the live vaccines. Get the okay from your veterinarian first before proceeding with this. The product that is chosen is dependent upon the management practice of the producer. Vaccines should be selected based on how individual herd conditions mesh with the advantages and disadvantages of the two types of vaccines. Most research on the new vaccines prove fetal protection on their labels.

Your local veterinarian can best advise about additional vaccines that maybe recommended against reproductive diseases in your area. Purebred herd managers may need to exercise particular caution as most purebred herds are considered open herds. Cattle are often taken to shows and displays, all of which increases their exposure to both respiratory and reproductive diseases.

Many abortions are incidental and due to trauma, stress, twinning, maternal illness causing death of the fetus, and congenital defects of the fetus with subsequent abortion. Therefore abortion is a common encounter for many producers. Co-operation between the producer, the veterinarian and the lab will maximize the opportunity to diagnose the cause of an abortion. A diagnosis is very important as future recommendations are often based upon this diagnosis. Preventive measures can then be taken where applicable. Keep in mind if cattle are trucked, go to shows or auction markets, the additional stress and potential exposure to disease can cause the abortion rate to raise. Also with purchased bred cattle try and get some history of their vaccination status against reproductive diseases.

RoyLewisisapracticinglargeanimal veterinarianattheWestlockVeterinaryCenter, northofEdmonton,AB.Hismaininterestsare bovinereproductionandherdhealth.

About the author


Roy Lewis is an Alberta-based veterinarian specializing in large-animal practice. He is also a part-time technical services vet for Merck Animal Health.



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