Calving difficulty, technically called dystocia, is a major cause of death loss in cow-calf herds. Dystocia is also the number one cause of calf mortality in the first 96 hours of life. Pregnancy rates for the dam after losing a calf are lower than for dams that have not lost a calf. Studies also indicate that animals experiencing dystocia while delivering a live calf may have decreased rebreeding rates.
The average length of gestation for cattle is 280 days, with a normal range of 273 to 296 days. A twin pregnancy will average 3 to 6 days less.
There are three stages of labour in normal calving:
First stage: The first stage of labour is when the cervix is dilating. This stage can last between 1 and 24 hours. Cows will often separate from the herd, and may be restless. They will not eat or drink and can have a vaginal discharge.
Second stage: The second stage begins when the cow starts contracting and continues until the calf is delivered. The amniotic sac, or water bag, will appear at the vulva. The foetus starts to enter the birth canal, which then stimulates contractions that can be seen as abdominal press. The delivery should be complete within 2 hours after the amniotic sac appears
Third stage: The third stage is when the placenta is delivered. The placenta usually passes within the first 8 hours after birth. It is considered “retained” at 12 to 24 hours, but manually removing the afterbirth is not recommended.
Dystocia is when it becomes difficult or impossible for the cow to deliver the calf without assistance. It can occur in the first and/or second stage of labour. You may not know the exact time the cow goes into labour, but careful observation, and knowing the general guidelines will help identify dystocia’s early.
Causes of Dystocia
The most common causes of dystocia are maternal/foetal disproportion, abnormal position of the calf during delivery, incomplete dilation of the cervix, uterine inertia, uterine torsion, twins, and abnormal foetuses.
The most significant cause of dystocia is maternal/foetal disproportion. This is a condition when the calf is too large for the female to deliver without difficulty. Heifers are at the greatest risk of maternal/foetal disproportion. Improper nutrition not only result in heifers being too small at breeding, but also may compromise the amount of energy available for labour. Undernourished heifers are more likely to become exhausted and have prolonged deliveries. In contrast, heifers that are too fat may have difficulty delivering calves because of the excess fat in the birth canal.
If the amniotic sac appears at the vulva, then a good rule of thumb is the calf should be born within 2 hours. For a mature cow, it will probably be closer to 1 hour. If you do not know when the animal began labour, the most reliable way to assess if the animal is having trouble is the progress it is making. A cow or heifer should be making visible progress every 20 to 30 minutes that she is in active second-stage labour. One that frequently tries to urinate or walks with her tail up and extended for more than 3 to 4 hours may have a uterine torsion (twisted uterus), an abnormally positioned calf, or other condition that blocks passage of the foetus and membranes so they are not visible.
If there is an extended second-stage labour or the animal is not making progress or frequently assumes a urinating posture over several hours, it needs to be examined. When examining a cow, good sanitation is very important future reproductive problems. You will need proper restraint for the animal that should include access to a chute and headgate. Clean the vulva with a mild soap and water and wear plastic OB sleeves to protect both the cow and you from infectious agents. The vulva should be relaxed and free of obstructions like fat and pelvic fractures, and the cervix should also be relaxed and dilated large enough for the calf to pass through. When you pass your hand along the birth canal, there should not be any band marking the border between the birth canal and uterus, that is, you cannot identify the cervix. Next, determine the position and size of the calf. The normal position for a calf during delivery is both front legs extended with the head following and facing forward in a “diving” position. If the cow is dilated and the calf is in the normal position, but still no progress is being made, maternal/foetal disproportion is likely. Never attempt to deliver a calf in an abnormal position without first correcting its presentation as you could cause irreparable damage to the cow.
Because many of the causes of dystocia, such as abnormal calf position and uterine torsion, are sporadic and unpredictable, prevention focuses primarily on correcting foetal/maternal disproportion and nutrition.
There are two factors to consider with maternal/foetal disproportion: the size of the dam at calving, and the size of the calf. Because heifers are generally smaller than cows, they have an increased risk of dystocia.
Nutritional Approaches To Meeting Target Sizes
Developing proper diets and feeding strategies for meeting the target weights is critical. However, diet recommendations need to be based not only on the required rates of gain for heifers to meet target weights but also the nutrient quality of the base forage.
Decreasing Calf Size
Decreasing the calf size will also significantly help prevent dystocia’s. Some breeds, such as Longhorns, have smaller birth weights, but, unfortunately, they also have less growth. For most producers this is unacceptable. In the bovine, the heritability of birth weight is almost 48 percent. That means the female alone doesn’t control or “limit” the size of the calf. Therefore a cow bred to a bull that produces large calves may have a large calf regardless of her size.
Pregnant heifers and cows should be in good condition, especially in the last one-third of their pregnancy. Increasing the energy content in late pregnancy may have some helpful effects on shortening labour times and decreasing dystocia. Conversely, cows that were fed a severely restricted protein diet in late pregnancy had higher calf deaths and dystocia’s. For spring calving herds, heifers and cows are in late pregnancy during mid to late winter. If these females have only been fed average- to poor-quality hay throughout the winter, they may enter the last trimester of pregnancy with a thin body condition. By the time they are due to deliver, they have a greatly increased chance of having problems with dystocia’s, calf deaths, or becoming a down cow. Because heifers have higher nutritional needs than cows, they should be housed/pastured and fed separately during the last 2 to 3 months of pregnancy. This will also prevent cows from being overfed, which has also been shown to increase the likelihood of dystocia.
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