Fertility is one of the major causes of losses in dairy cows. The losses include reduced milk production and a high cost of feeding and replacement of animals.
One of the major problems associated with fertility is abortion, which generally means termination of pregnancy.
However, it is important to note that early embryonic deaths and stillbirths are not forms of abortions.
The former is pregnancy loss before the full formation of the calf’s internal organs; 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.
Abortion, therefore, is the pregnancy loss between 42 and 260 days; where pregnancy is indicated by rectal palpation 35 to 40 days after service.
Most abortions occurring during the second and third months go undetected until the cow fails to calve or return to heat.
However, abortions after the fifth month are frequently characterised by retained placenta, the cow failing to shed the foetal membranes for up to two weeks but abortions before fifth month often have few external signs and are seldom followed by retention of the placenta.
CAUSES OF ABORTION
The most frequent are infectious agents such as bacteria like brucellosis, leptospirosis, salmonellosis, haemophilussommus, mycoplasma and listeria. Others include viral agents such as bovine viral diarrhoea and infectious bovine rhinotracheitis; fungi and mycotoxins; genetic abnormalities, environmental stresses like excess heat, fungi and protozoal parasites like Neosporacaninum, injuries and use of abortifacient drugs such as prostaglandin, glucocorticoids or oestrogen in treatments.
Poison such as iodine and toxins in plants are other causes of abortion. A few abortions are further caused by eating mould in feeds like hay or silage. Moulds are dangerous to the foetus especially during the third through to the seventh month of gestation. Abortions due to vibrio bacteria and trichomoniasis disease occur sometimes during the first four months of pregnancy. The affected cow returns to heat but does not settle until she recovers from the infections after several heat cycles. High fever is another possible cause of abortion.
Though abortions in the herd at a rate below 5 per cent may be considered normal, generally the infectious causes involve mass abortions of more than 10 per cent of cows.
Stress often triggers the release of hormones in the body of the cow, causing labour, then premature calving. Usually, when a cow aborts following an 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 foetus protecting it from trauma even if the cow is injured seriously.
In case abortion occurs, call a veterinarian to select and prepare proper samples to submit to a laboratory. Good sample sources include the whole foetus and the foetal 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 helps increase the chances of diagnosing the causes of abortion. All abortion cases should also be reported to your area animal health office.
All abortion prevention programmes start with herd health management. This include;
a) Laying bio-security measures: This minimises the risk of introducing diseases on the farm or spread within the herd. Bio-security involves purchasing effectively quarantined herd only, giving special attention to the health status of bulls to avoid introduction of diseases and venereal spread, using disinfectants for visitors coming into the farm and isolating aborting cows and immediate removal of aborted materials.
b) Proper feeding: Provide sufficient quantity of a properly formulated and delivered ration, offer high quality feeds to pregnant cows, avoid contaminated feeds and store feeds safely from vermin as they can spread bacteria and viruses. Also provide clean water and ensure a clean, dry animal environment.
c) Vaccination: This is an integral component of a complete herd health programme. It involves vaccinating your herd against most of the infectious diseases causing abortions.
For pregnant cows or calves, intranasal vaccination is usually considered safe. Since most abortions resulting from vaccination occur between two to 10 weeks after injection, vaccinate cows annually when they are not pregnant and young stock at weaning for them to start building immunity.
d) Control use of breeding bulls: Natural mating with infected bulls spreads diseases associated with abortions such as trichomoniasis hence the use of artificial insemination to control these diseases is advisable.
e) 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.
Disinfect the instruments and control insect vectors to reduce abortions.
By FELIX OPINYA