The Namibia Agricultural Union has warned farmers of the occurrence of large numbers of cattle abortions in the Windhoek district of late.
According to the union's latest newsletter, reports of these abortions have come from various farms, with losses ranging from five to 45 and even 128 calves on some farms.
According to the union, it is suspected that these abortions occur wider than expected. Numerous samples have been submitted to the Windhoek Central Veterinary Laboratory as well as to Onderstepoort and Path Care in Cape Town.
"So far only the bacterium Enterococcus casseliflavus has been identified, which, according to literature, is not known to cause abortions. Tests for other known venereal diseases have been negative so far," the union said.
Although most of the abortions that were reported have taken place between three and six months, there were also reports of older calves aborted. It seems that symptoms vary, but one is a high fever of the cow shortly before aborting.
"Government and private veterinarians are working closely to identify the cause of these abortions. As much as possible information is needed and it is crucial to report any incidents of cattle abortions to the laboratory or veterinarians," said NAU.
Abortion in cattle is commonly defined as a loss of the foetus between the age of 42 days and approximately 260 days.
According to the Virginia-Maryland College of veterinary medicine in the US, a low rate of abortions is usually observed on farms and 3 to 5 abortions per 100 pregnancies per year is often considered "normal." However, the loss of any pregnancy can represent a significant loss of (potential) income to the producer and appropriate action should therefore be taken to prevent abortions and to investigate the cause of abortions that may occur.
Each abortion is estimated to cost the producer, depending on such factors as the current value of replacement stock, feed and the stage of gestation when the abortion occurs.
The diagnosis of abortions often presents a challenge to the herd owner and the veterinarian. Although a gradual increase in the abortion rate in a herd may be noted over a period of many years, a sudden and dramatic increase is more commonly seen. For this reason, prompt and thorough action is required when abortions do occur. Well kept records will often be of benefit during the investigation of abortion problems. While infectious agents are perhaps the most frequent cause of bovine abortion, there are other factors which may cause a proportion of pregnancies to terminate with an abortion.
Genetic abnormalities in the foetus that may result in abortion are not very frequently diagnosed, and these usually occur as an individual cow problem rather than as a herd outbreak. These abnormalities, which may not cause a change in the outward appearance of the fetus, may result in abortion because of the growing fetus' inability to develop properly in the uterus.
Genetic abnormalities may also cause obvious physical changes in the foetus , just as other infectious agents may.
Heat stress can affect reproductive performance in a dairy herd, although it will generally cause conception problems rather than abortions.
While there is some evidence to suggest that a very sudden increase in environmental temperature may result in abortions, there is little evidence to support heat stress as a common cause of abortions. Similarly, on rare occasions a cow that develops a very high fever due to an infection may abort her foetus .
Toxic agents may also cause abortions or early embryonic deaths. Cattle are susceptible to fertiliser nitrites and nitrates or the nitrates found in plants under certain conditions (e.g. drought-stress). If a cow is exposed to sufficiently high levels of nitrates/ nitrites, abortions may occur, especially in late gestation.
Some experimental studies have shown that mycotoxins such as zearalenone in very high levels can cause abortions in cattle, although these levels are not normally found in "naturally contaminated" feedstuffs. Likewise, the only reports of abortions associated with a toxin appear to be situations where the health of the cow was also severely compromised by the toxin.