Pregnancy may be terminated prematurely, resulting in abortion due to death of the conceptus or failure of the uterine environment to support the fetus. Abnormal fetal development may result in abortion or in a calf that dies soon after birth. Many cases of bovine abortion are not diagnosed. (Also see Abortion in Large Animals.)

Etiology

Viruses, bacteria (including rickettsia and chlamydiae), molds, protozoa, or other infectious agents may attack the placenta or the fetus, or both. Some of these microorganisms reach the uterus hematogenously; others (such as venereal infections) are contracted during mating.

Infectious abortion may be sporadic or a herd problem. Herd problems usually are associated with significant losses and may be caused by infectious bovine rhinotracheitis, bovine viral diarrhea, brucellosis, leptospirosis (various serotypes), campylobacteriosis, trichomoniasis, anaplasmosis, ureaplasmas, mycoplasmas and others not yet identified.

Mycotic abortion usually is caused by Aspergillus or Mucor spp, which reach the uterus hematogenously and cause abortion in late gestation. In many of these fetuses, the skin is not affected; in others, ringworm-like lesions are seen. The placenta frequently is severely affected with necrosis of the cotyledons and thickening of the intercotyledonary areas. Diagnosis is based on identification of the fungus through culture of the fetal or placental tissues, histologic examination of these tissues, or direct examination of cotyledons after clearing with potassium hydroxide solution. These abortions are almost always sporadic, and the only means of control is to reduce exposure to the fungi.

Sporadic losses may result from Listeria sp (a bacterium occasionally present in silage when pH is >7); miscellaneous bacteria such as Haemophilus sp, Arcanobacterium pyogenes, Staphylococcus aureus, Bacillus cereus, Pasteurella multocida, Pseudomonas aeruginosa, Streptococcus bovis, Chlamydia sp, and others; or viruses (eg, bluetongue).

Noninfectious causes of abortion are numerous; the most common include: 1) recessive or lethal genes (or both), hydrocephalus, osteopetrosis (“marble bone” disease), arthrogryposis (“crooked calf” syndrome), and several others, some not fully identified; 2) toxins (eg, excessive nitrates from feed or water), certain pine needles, poisonous plants (eg, lupine, locoweed), or mycotoxins (moldy feeds); 3) hormonal imbalances in the pregnant dam; 4) injuries affecting the pregnant cow; and 5) nutritional deficiencies, particularly of vitamin A, vitamin E or selenium (or both), iodine, and manganese.

Heat stress in cattle can cause early embryonic death and lower the herd pregnancy rate. The mechanism by which heat stress affects embryonic survival is complex. Heat stress can disrupt early embryonic development. Effects of heat stress on embryonic survival decrease as embryos advance in development. Heat stress at day 1 or days 1–3 after breeding reduces embryonic survival. In contrast, heat stress of superovulated cows at day 3, 5, or 7 after estrus did not affect embryonic development in one study.

Diagnosis

Accurate diagnoses of reproductive loss contribute to the cumulative herd history and provide criteria for evaluating the impact on herd performance, and the need for implementation of preventive measures. Laboratory assistance is needed in most cases. Carefully selected, properly preserved, quality specimens should be submitted to a diagnostic laboratory for analysis. Even with these, the exact cause of an abortion may not be detected, especially if it is noninfectious. Many infectious causes can be excluded, however, which assists in formulating a preventive strategy. Laboratory diagnosis of abortion requires both serology and examination of the fetus and placenta. For serology, paired blood samples should be collected from the aborting dam, with the first sample taken at the time of abortion and the second 10–14 days later. An absolute diagnosis may be impossible because, in many cases, the causative agent may not be present when abortion occurs.

Defective newborn calves can be recognized only by a thorough examination and sometimes only after some time has passed.

Prevention and Control

Several factors are critical to prevent and control abortion and development of defective calves. A balanced nutritional program helps control losses associated with mineral or vitamin deficiencies and poor-quality feeds, including moldy grains and forages. Genetic selection and accurate record-keeping help to detect and eliminate bloodlines that prove to be carriers of recessive or lethal genes. Appropriate housing and handling facilities decrease the incidence of accidents and provide an environment conducive to health. The cattle producer and veterinarian should work together to assess the herd's reproductive performance, tailor a vaccination program to the herd's specific needs, and diagnose and control potential herd problems.

For successful abatement of heat stress, the environment of the cow must be modified to maintain the cow within a normal temperature range of 101.3–102.8ºF (38.5–39.3ºC). Common approaches include providing shade (to intercept solar radiation) and fans or sprinklers to promote evaporative cooling.

Infectious diseases in a herd can disrupt and reduce reproductive efficiency by causing embryonic or fetal death, abortion, or illness and death of neonates. A complete vaccination program will not eliminate reproductive problems but may prevent or reduce losses associated with specific infections (see Management of Reproduction: Cattle: Immunization Program to Protect Against Prepartum Diseases of the Breeding Herd and Table 2: Management of Reproduction: Cattle: Immunization Program to Protect Against Diseases of the Neonatal Calf).

Table 1
PrintOpen table in new window
Immunization Program to Protect Against Prepartum Diseases of the Breeding Herd Disease When to Immunize Heifers Brucellosis Calfhood IBRa, BVDb Before weaning and before breeding Campylobacteriosis, leptospirosis, trichomoniasis Before breeding Cows IBR, BVD May booster early before breeding Campylobacteriosis, leptospirosis, trichomoniasis Each year, before breeding Bulls IBR, BVD Calfhood and booster before first breeding Campylobacteriosis, leptospirosis Each year, before breeding a Infectious bovine rhinotracheitis b Bovine viral diarrhea

Table 2
PrintOpen table in new window
Immunization Program to Protect Against Diseases of the Neonatal Calf Disease When to Immunize Heifers and cows Rotaviruses and coronaviruses, Escherichia coli bacterins, clostridial bacterins As on label Calves Rotaviruses and coronaviruses (if indicated) As on label

Last full review/revision July 2011 by Carlos A. Risco, DVM, DACT