Managing Dystocias In Bison

Dr. John Berezowski
Western College of Veterinary Medicine
Saskatoon, Saskatchewan
Reprinted from Smoke Signals, December 2000, pages 12-16


This presentation was originally given at the International Bison Conference 2000, in Edmonton, Alberta. Dr. Berezowski explains calving problems (dystocias) in bison and tells you what you can do when faced with this problem. He also explains some of the common problems that cause dystocia in bison.

In general bison cows have very few calving problems. When they do have problems the outcome is often disastrous.

Normal Calving

One of the first signs of impending labor is that the cow will hold her tail elevated and well away from the opening of her vulva. The cow may also grunt, roll, paw the ground or kick at their belly. Bison cows may or may not leave the herd to deliver their calves. Some cows especially those that are in a calving areas that has no cover will often deliver their calf in the middle of the herd. If there is bush in the calving area cows will more frequently move away from the herd and deliver their calf by themselves in the bush.

As parturition progresses, the cow will usually begin to strain while in a standing position, with her back humped. Shortly after the cow begins to strain, the amnion or water bag will appear. Occasionally bison cows deliver their calves standing, but in most cases the cow will lay down on her side with her feet extended. As she strains the cow will often lift her head and look back- wards. When the calf starts to emerge the cow will frequently elevate her upper back leg. As soon as the calf is born the cow will stand over it and lick it continually until it stands and nurses.

How Long to Wait

It is difficult to make broad recommendations about how long to leave a calving bison cow before trying to provide her with assistance. In some cases it is very easy to make a decision. A cow with a calf's head and no feet hanging out of her vulva is quite likely to need assistance, and no further waiting is required. In other instances it is not as easy to differentiate between a cow that requires assistance to one that is just taking a long time with a normal delivery.

In one small study, bison cows took from 18 to 197 minutes to deliver their calf after the water bag was observed. They also took from 1 to 40 minutes to deliver their calf after the calf's feet were first visible. This was a study of free ranging bison, but if we apply these numbers to farmed bison cows it would be recommended that bison cows be allowed a minimum of 3 1/2 hours to deliver their calf after the water bag is observed, and a minimum of 40 minutes once the calf's feet are observed. It was also found in this study that bison cows could delay labor for long periods of time if they were disturbed. Observation of calving bison should be done from a long distance. If you are close enough to cause the cow to get up, you have interrupted her labor and will delay the delivery of her calf.

The incidence of dystocia in bison cows is very low. Bison cows are often able to deliver calves that are in abnormal positions. For these reasons bison producers often allow calving cows a considerable amount of time to work things out before they consider providing assistance. In most cases of calving trouble the calf will be dead before the cow has been identified as having a problem. If the calf is not dead, it will usually not survive the cow being aggressively chased into a handling facility. If the calf is dead, then time is not as critical, and the cow can be left for a period of up to 6 or 8 hours. It is important however, not to leave the cow for too long. As the length of time the cow is in labor increases, fetal fluids will be lost and the calf will become very dry and hard to work with. In some cases leaving a calving cow for a long period of time can cause serious problems for the cow. The calf can become bloated and will release toxins that can make the cow very sick. If this happens the calf must be removed or the cow will die.

What To Do

Since it is likely that the calf is already dead the major goal of providing assistance to bison cows with dystocia is to save the cow. Once a cow has been identified as having a calving problem that won't resolve with out intervention, the cow must be captured and restrained so that assistance can be provided. Since calving cows have a larger flight zone than non-calving cows, plenty of time should be taken to bait the cow or to slowly and calmly work her into a handling facility. It is important to not aggressively chase the cow, because bison cows that are worked up are less likely to respond favorably to tranquilizers. This can be very important if the cow can't be captured and the only way to provide assistance is to tranquilize her in the field. Once the cow is restrained in a squeeze or is tranquilized, assistance can be provided. The calf should be pulled as quickly as possible to minimize the amount of time the cow spends in the squeeze. The longer she stays in the squeeze the less likely will be her chance of survival.

Bison cows will often lay down if they are held within a squeeze for any time longer than a few minutes. If a hydraulic squeeze is not available, ropes can be tied under the cows belly to act as a sling that will hold the cow up during the procedure.

The cows' vulva should be washed with warm water and bactericidal soap. A vaginal exam should be performed to determine the cause of the dystocia. Large amounts of lube are often required as the calf is often very dry and there is very little fluid in the uterus. If the head or legs are required to be manipulated, they should be done so with care, as aggressive movements can cause the uterus to rupture. If the calf can be pulled it should be done in a slow, steady manner, as pulling the calf too quickly can also cause the uterus to rupture. If the malpresentation cannot be corrected by manipulation, a fetotome can be used to cut off a leg that is held back or a head that is turned. In some cases the entire calf can be cut apart and removed in pieces. Longer procedures however, will reduce the cow's chance of surviving.

Caesarian sections should be considered as a last resort. The chances of a bison cow surviving a c-section are very low.

Types of Dystocia


Malpresentations are any fetal positions at birth that deviate from the normal. The normal fetal position at birth is the position most commonly observed when a bison cow delivers a calf. The first sign of the fetus is the tip of the toes, followed by the head. If the cow is standing during delivery the calf is in an upright position as it is being born and the head is on top of the front feet. The causes of malpresentation are not known.

Backwards Presentations

Backward presentations in which both back feet are delivered first might be considered to be an abnormal presentation, however, bison cows should be able to deliver backwards calves without any problems.

Breach Presentations

Breach presentations are backwards presentations in which the back feet are tucked up underneath the calf's abdomen so that the only part of the calf that appears is the tail. Bison cows are not able to deliver breach calves on their own. Breach presentations are hard to detect. In some cases the tail remains inside the uterus and is not visible. If the tail is exposed it often goes unnoticed, and the only sign that there is a problem is that the cow remains in labor for a long period of time without delivering her calf. After a day or two the cow will stop straining and appear to go out of labor. The outcome of undelivered breach calves is not always known. The dead calf ultimately decomposes within the uterus. In some cases the decomposed calf will release toxins that can make the cow very sick, and cause her to die. These are the cases that we are aware of. However, because breach calves often go unnoticed by producers it is possible that breach calves decompose without making the cow sick. The decomposed calf may be passed out of the uterus sometime later, as a soup of bones and hair.

Head Back Presentations

Head back positions are presentations in which the front feet appear first but the head is turned to the side or down between the front legs. Bison cows are unable to deliver calves in this position without assistance. Head back positions are easily identified. Cows attempting to deliver a calf in this presentation will remain in labor for a long period of time, with only the front feet visible. Head back presentations are corrected either by manually returning the head to normal position or by cutting the head off with a fetotome.

Leg Back Presentations

Leg back positions occur when the calf is presented nose first with one or both of the front legs held back along the side of the calf. Leg back presentations are easily identified. If one leg is back the head and one leg will be observed hanging out the back end of the cow. If both legs are back the head without any legs will be observed hanging out the back end of the cow. If the calf is very small it is possible for the cow to deliver a calf that is presented in one of these positions. If the calf is large the cow will need assistance. If both of the legs are back, the head must be cut off in order to push the calf far enough back into the uterus to allow the legs to be pulled forward. If one leg is back the calf may be pulled, in others the leg that is held back must be cut off with a fetotome.

Oversized Fetuses or Maternal Fetal Mismatch

One of the most common causes of dystocia in beef cattle is calves that are too large to pass through the pelvis of the cow. The increase in size of cattle fetuses is a direct result of the manner in which cattlemen have selected breeding stock. They have selected replacement heifers and breeding bulls almost entirely based on growth parameters, such as weaning weight, yearling weight and adult weight.

By selecting the biggest and most rapidly growing animals as breeding stock, cattlemen have inadvertently selected cattle that produce calves with large birth weights.

Within the bison industry oversized calves have not been a major cause of calving problems in the past. During the last few years however, oversize calves have become a more common cause of dystocia in bison. If the bison industry follows the beef industry and focuses selection of breeding stock exclusively on production parameters such as weaning weights, yearling weighs and two year old weights, oversized calves will become a much more significant cause of dystocias in bison.

Over/at Cows

Free ranging bison and elk cows lose weight during the winter months, and generally are thin when they enter the calving season. Both farmed elk and bison are provided with better quality feed than would be available under free ranging conditions. Feeding elk better quality feed during the winter has resulted in some elk cows becoming over fat at calving time. Often fat elk cows can, and frequently do have difficulty delivering their calves. Farmed bison cows like farmed elk cows often come through the winter in much better condition than they would if they were free ranging. In most cases bison cows are not fat enough to have difficulty delivering their calves. However there are some bison herds which experience calving problems that are a direct result of their cows being over fat at calving season. Bison producers should be cautions, and not allow their bison cows to become too fat during the winter.

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