The key to correcting the problem of abortions is to identify the cause, so abortions can be prevented in the future. However, the success rate for accurate bovine abortion diagnosis is only in the range of 25-35%.
Abortions often result from some incident that occurred weeks to months before the actual abortion. As a result, the cause is probably undetectable at the time of the abortion itself. In fact, many causes of abortions are unknown.
Mycotic (caused by mycotoxins) abortions may be seen in increased numbers in spring, due to cattle consuming moldy feed contaminated with mycotoxins. These abortions are typically sporadic and occur from four months to term.
Severe infection of the placenta will be seen, characterized by a leathery thickening of the areas in between the cotyledons. In about 25 per cent of the cases, the fungus invades the fetus, and red or white ring-worm-like lesions can be seen in the fetal skin.
If the fetus remains in the uterus for any length of time after death, postmortem degeneration will hide lesions. The afterbirth may be retained, causing even more problems.
As a preventative measure, it is essential to develop a checklist to help you and your veterinarian explain and diagnose potential abortion problems.
Key Questions To Ask
What is the problem?
Is it a failure to conceive or were the fetuses lost? Were the cattle pregnancy-checked? Or were the cattle open? Pregnancy failure rate in cows and heifers should be less than 5 per cent as a production-loss goal.
Which animals are involved?
What is the difference between the groups of cows that conceived and calved and those that did not? Were the cows home-raised or were new animals brought into the herd? Are the cows in good or poor body condition?
What age groups are affected?
What is their vaccination status? Were modified live or killed vaccines used? Modified live vaccines may cause abortion if given to pregnant cows or to calves nursing previously non-immunized cows; such a program must be initiated carefully.
What are they fed?
Type, quality and condition of feed are all important factors to consider in abortion prevention. Moldy feed causes 3 to 10 per cent of all abortions. Remember, the inhalation of mold spores is just as dangerous as the consumption of them. Vitamin A deficiency may also cause abortions.
What bulls were the cows exposed to?
Consistency of performance throughout the breeding season and the exposure to sexually transmitted diseases (STDs) are issues that should be looked at, especially if the animals were on a community pasture. STDs that cause abortions include Brucellosis, Listeriosis and Trichomoniasis.
Do the affected cows have a common sire or dam?
When did the problem occur?
Were the fetuses lost at a certain stage of gestation?
A loss in the last month of pregnancy could be due to nitrates in the feed. Handling, trucking or any kind of stress may also trigger abortions.
Did it occur on pastures or when their feed was changed? Was this feed tested?
Was the feed free of nitrates? Abortion due to nitrates is accompanied or preceded by some evidence of nitrate problems in the adult animal, including chocolate-colored blood and bluish discoloration of non-pigmented areas of the skin or mucous membranes.
Were many cows affected suddenly, or did the problem pass through the herd slowly? Typical abortions occur at low levels of about 2% and are usually seen at the beginning of calving.
Where did the problem occur?
Did affected and unaffected animals reside in different pastures, paddocks or ranges? What were the field conditions and the stocking densities? Did the animals have to compete for feed and water?
Identify the cow that aborted and isolate it. Recover the aborted fetus and membranes. The length of gestation can be determined by fetus size and other characteristics:
2 months - mouse size
3 months - rat size
4 months - small cat size
5 months - large cat size
6 months - small dog size with hair starting to show
7 months - fine hair all over body
8 months - hair coat complete and teeth slightly erupted
9 months - incisors erupted
Submit as many fetus samples as possible to a diagnostic lab. The first calf to die is the most important; getting a diagnosis on this one may help to avoid any more abortions in the herd.
Call the veterinarian as soon as possible and keep him/her involved in the entire process. Notify the lab that you have a specimen to sample and send in to analyze. Collect samples; preferred specimens include fetus and blood samples from cow(s) that aborted.
The liver is often affected by abortive agents and should be examined and sampled. Lungs should also be sampled because they receive a good blood supply and will show any inhalation of bacteria in later gestation and fetal pneumonia.
Pack the fetus and placenta in double set of heavy-duty plastic bags and pack in ice (do not freeze), along with any blood or tissue samples. Get the package to the diagnostic lab as quickly as possible.
Without answers to the above questions, a veterinarian will have a difficult time trying to give a complete diagnosis. In addition, answers to these questions will help a producer determine whether a change in management practices is needed.