Abortion can be one of the greatest sources of loss to the cow-calf and purebred beef producer from fall onwards. There are a great number of causes for abortion. Unfortunately some 25 to 50 per cent of these causes go undiagnosed. This article outlines the most common causes of abortion in beef cattle and discusses those factors that are responsible for obtaining a definitive diagnosis.
Abortions may occur in the early stages of pregnancy but only be revealed when the cow is open at pregnancy-checking time. If a high percentage of open heifers or cows are found at this time your veterinarian may want to pursue various forms of testing to identify the cause.
If bull evaluations do not reveal any deficiencies then the cow herd becomes the focus of the investigation.
Nutritional status of the herd is the first thing to question 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’s important to realize that abortions stem from problems not only with the individual fetus, but also with environmental and maternal factors.
Since 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 procedures that can provide some answers.
To even get to that point it is important that the aborted fetus be as fresh as possible. This can be vital to obtaining an accurate result.
Submitting the placenta as well doubles the chances of gaining a diagnosis. Of course, it should also be as fresh as possible.
Gather the fetus and the placenta in separate, clean plastic bags and keep them cool. If the cow still has retained some placenta, gently pull it out until you can be sure your sample contains a cotyledon, then snip it off. The cleaner the sample, the better. Obtaining a diagnosis from aborted fetuses and placenta contaminated with soil, straw, and manure is a diagnostic challenge and one that is often unrewarding.
An abortion rate of two to three per cent over the latter stages of pregnancy is considered normal. However abortions that occur close together may be a concern. Watch closely around six months gestation for telltale signs of abortion such as a wet tail or retained placenta.
When several abortions have occurred at the same time your veterinarian will want to pursue a history of what has been going on in the herd in an attempt to diagnose the problem. This will involve a detailed review of the nutritional status and vaccination protocols, new heifers or cows introduced to the herd, and environmental conditions. All of these are vital to understanding the nature of the problem.
The body condition of the cows/ heifers that aborted and their herd mates will need to be evaluated, as well as blood samples. 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 a BVD infection depend on when the virus comes into contact with the fetus. If the fetus is exposed before 100 days of gestation, abortion and mummification are the usual outcome. If contact occurs in the middle third of the pregnancy, congenital abnormalities of the nervous system and eyes are evident. Contact in the last trimester generally results in normal healthy calves with titres against BVD or live persistently infected calves that will continue to shed the BVD virus during their lifetime.
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. Very accurate DNA tests are now available on blood or semen from bulls or manure that can help pinpoint these infections in a herd.
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 to pregnant animals but requires two shots the first year and annual vaccination in subsequent years. The second is a modified-live vaccine. It gives better immunity than the killed vaccines, is less expensive and is best given just before breeding season.
If the BVD and IBR vaccine status is protective cows can be vaccinated in late pregnancy with most of the live vaccines. Get the OK from your veterinarian first before proceeding with this option. The product that is chosen is dependent upon the management practices 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 support fetal protection. Check the labels.
Your local veterinarian can best advise you as to additional vaccines that may be 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 undertaken where applicable.
Keep in mind, if cattle are trucked 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.