Fertility is one of the major causes of economic loss in the dairy cattle industry. The losses are in form of reduced milk production, high feeding and replacement costs. In response, dairy farmers are becoming concerned about pregnancies lost especially through abortion and get eager to better understand possible causes and how to prevent it. Abortion generally means termination of pregnancy; though there are other causes of pregnancy loss like early embryonic deaths and stillbirths.Early embryonic death is pregnancy loss before formation of the calf’s internal organs is complete; usually occurring around 42 days of gestation while stillbirths occur anytime a calf dies from 260 days of gestation up until 24 hours after calving. A true abortion hence, is the pregnancy loss occurring between this periodof 42 and 260 daysof pregnancy; where pregnancy is indicated by rectal palpation 35-40 days after service.Most abortions occurring during the second and third months go undetected until the cow fails to calve or returns to heat. Howeverabortions after the fifth month are frequently characterized by retained placenta, the cow failing to shed the fetal membranes for up to two weeks but abortions before fifth month often have few external signs and seldom followed by retention of the placenta.
Causes of abortion
There are multiple causes of abortions in dairy cows; the most frequent being infectious agents such as bacteria like Brucellosis, Leptospirosis, Salmonellosis, Haemophilussommus, Mycoplasma and Listeria. Other infectious agents include viral agents such as Bovine Viral Diarrhea (BVD) and Infectious Bovine Rhinotracheitis; fungi and mycotoxins; genetic abnormalities; and environmental stresses like heat stress. Though abortions in the herd at a rate below 5 percent may be considered normal, generally the infectious causes involve mass abortionsofmore than 10% of cows aborting. Other agents which can cause abortion are fungi, protozoal parasites like Neosporacaninumand use of abortifacient drugs such as prostaglandin, glucocorticoids or estrogen in treatments.
Some abortions in late pregnancy are also due to injury or extreme stress. Stress triggers the release of hormones in the body of the cow causing labor then prematurecalving. Usually when a cow aborts following injury, it is caused by stress like pain or even inflammation rather than the injury itself since the uterus and its fluids cushion the developing fetus very well and protecting it from trauma even if the cow is injuredseriously.Poisons such as iodine can be another cause of abortion. Toxins in certain plants or plant parts such as branches that is easy to reach, logging slash, windfalls among others. A few abortions are caused by eating mold in feed like moldy hay or silage. Molds are dangerous to the fetus especially during the third through seventh months of gestations. Abortionsduebacteria vibrio andtrichomoniasis diseaseoccur sometime during the first four months of pregnancy. The affected cow returns to heat but does not settle again until she recovers from these infectionsafter several heat cycles.High fever is another possible cause of abortion.
It may be difficult to determine the cause of abortions due to lack of samples evidences. In case abortion occurs, call a veterinarian to select and prepare the proper samples to submit to a laboratory. Good sample sources include the whole fetus and the fetal membranes, the placenta or a blood sample from the aborting cow. Keeping accurate records such as when a cow was due to calve, last abortion incidence and vaccination status of the cow helps increase the chances of diagnosing the causes of abortion. All abortion cases shouldalso be reported to your area animal health office.
All abortion prevention programmes starts with herd health management by employing different cases in terms of;
- Laying bio-security measures: this minimizes the risk of introducing diseases onto the farm or spread within the herd. Bio-security is through purchasing effectively quarantine herdonly, giving special attention to the health status of newly purchased bulls to avoid disease introduction and its venereal spread, using disinfectants for visitors coming into the farm and isolating aborting cows and immediate removal of aborted materials.
- Proper feeding: Providing sufficient quantity of a properly formulated and delivered ration, feedinghigh quality feeds to pregnant cows, avoiding feedingfeeds contaminated with moulds and store feedsaway from vermin as they can spread bacteria and viruses.Systematically evaluate the feeds for mycotoxins and phytotoxins. Also provide clean water and ensure a clean dry animal environment.
- Vaccination: This is an integral component of a complete herd health program. It involves vaccinating your herd against most of the infectious diseases causing abortions. For pregnant cows or calves nursing pregnant cows, intranasal vaccination is usually considered safe. Since most abortions resulting from vaccination mostly occur between two to ten weeks after injection, vaccinate cows annually when they are not pregnant and young stock at weaning for them to start building immunity.
- Controlled use of breeding bulls: Natural mating with infected bulls spread diseases associated with abortions such as trichomoniasishence the use of artificial insemination to control these diseases is advisable.
- Disinfecting farm instruments and vector control: Insect vectors or unsanitary needles and dehorning instruments usually facilitate transmission of protozoan diseases like anaplasmosis,which destroy the red blood cells. In such cases, disinfect instruments and control insect vectors to reduce abortions rates.