When calving season begins, we always hope for a crop of calves to arrive with few issues. However, even in the best-managed herds, occasional late-term abortions or stillbirths are an unfortunate reality. These isolated cases often prompt producers to reach out for guidance.
A key question emerges: How can one distinguish between expected losses and signs of a more significant problem? Understanding this balance is crucial for maintaining herd health and productivity.
Distinguishing Between Abortions and Stillbirth
An abortion typically means pregnancy loss between 45 days and 270 days gestation. Earlier than 45 days is considered early embryonic death and is typically not detected by the producer. If there is a large number of early embryonic deaths, this can show up as a poor conception or pregnancy rate at pregnancy diagnosis. Calf loss between 270 days gestation and 48 hours post calving is classified as a stillbirth.
A handy trick to assess whether a calf is full-term or premature is to check the lower incisors of the calf. If they have not yet erupted through the gum, the calf is likely at least two weeks premature.
Potential Causes for Late- or Full-Term Loss of Calves
There are many potential causes for late- or full-term loss of calves. We had a challenging summer with extreme heat and drought affecting much of our area in June and July. There are a few ways that this can lead to pregnancy loss. Any extreme stress or injury to the cow can potentially trigger premature labor. Nutritional stress, including extremely poor body condition due to drought conditions, or mineral deficiencies can cause pregnancy loss as well. Finally, nitrate toxicity is a cause of abortion. Nitrates accumulate in drought-stressed plants, especially small grains, which make this a greater concern during times of weather stress.
Calving difficulty (dystocia) can also be a cause for stillbirth. Calf factors, such as large size or abnormal position, and cow factors, such as small heifers, as well as over- or under-conditioned cows, can all contribute to prolonged delivery. Meconium staining, which is a yellow staining of the fluid and calf, is an indication of fetal stress during delivery. To reduce the impact of dystocia on calf viability, check cows at least twice daily and heifer three times daily during calving season. Know the signs that intervention is needed.
There are many infectious causes of abortion, as well. There are effective vaccines for some, but not all. Leptospirosis, Bovine Viral Diarrhea (BVD), and Infectious Bovine Rhinotracheitis (IBR) are all common agents that can cause abortion that we can effectively prevent through vaccination. There are many other potential causes of abortion including non-specific and non-contagious bacteria, fungal infection and protozoal infection. Tick-borne diseases Anaplasmosis and Theileria are common this time of year in our area and do not directly cause abortion, but cause low circulating blood oxygen (hypoxia) in the cow, which can lead to pregnancy loss.
The question of when action should be taken in the face of calf loss can be challenging and sometimes hindsight is 20-20. The reality is that when an aborted or stillborn calf is submitted to the lab, a diagnosis is found less than 50% of the time. That said with no lab submission, there is zero chance of finding a causative agent. As a rule of thumb, an abortion rate greater than 2% of the herd is considered a trigger for action.
Steps for a Successful Lab Diagnosis
The placenta is the most fruitful tissue in an abortion work up. To maximize the chances of a successful lab diagnosis follow these steps:
Collect the placenta in a garbage bag and submit with the calf for testing.
The placenta and calf must be kept cool, but not frozen, and delivered to the lab as soon as possible. Once the calf begins to break down, successful diagnosis is very unlikely.
Wear gloves when handling aborted tissues because some of the infectious agents involved are zoonotic and can cause serious disease in humans.
In case of an abortion storm, consider isolating affected cows and moving pregnant cows to fresh pasture.
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