Calving abnormalities have potential to impede birth process
Occasionally, difficult calving is caused by an abnormality in the fetus. Dr. David Steffen, diagnostic pathologist and professor at the University of Nebraska’s School of Veterinary Medicine says a common problem is discrepancy between the size of the calf and pelvic area of the dam.
Other problems are less simple. When checking a cow or heifer who is not progressing in labor, producers should keep in mind the possibility of an abnormality in which positional adjustments will still not allow delivery.
Some may be due to a congenital disorder or genetic defect in the calf which may be hindering the birth progress or making it impossible for the legs to be re-positioned to allow delivery.
Congenital defects
“Defects in the fetus, which may cause dystocia, are usually associated with effects on the muscular or skeletal systems,” says Steffen.
Some congenital defects are due to accidents in fetal development. Others are caused by teratogens or factors causing abnormality in a developing embryo or fetus. Teratogens include drugs, hormones, chemicals, viruses, toxic plants and high body temperature.
Many factors influence embryonic and fetal development. Vulnerability of the developing calf varies at different stages of gestation. Each organ and structure has a critical period of development during which it can be altered by harmful external influences.
“Dose, duration and timing are factors which determine the outcome and whether a teratogen will produce a birth defect. The dosage of the teratogen, the period of exposure and the time of gestation are key factors,” explains Steffen.
“One of the most disturbing defects is schistosoma reflexus,” says Steffen. “The spine is u-shaped, the top of the tail is close to the head and the fetus is turned inside out.”
“When reaching into the cow to try to determine what’s holding up progress, producers may find all four feet presented and may get a handful of intestines. They may think the uterus is ruptured and the intestines are from the cow,” he says.
Most of these malformed fetuses will not fit through the birth canal and must be removed surgically.
Lupine calves are another instance in which the fetus is malformed. Usually, lupine affects leg joints and limbs, but occasionally a producer will see a calf with a cleft palate.
Often, the legs are crooked or joints are fused and fixed so the legs don’t move properly. These defects are caused by certain alkaloids and can be attributed to the cow consuming lupine between 40 and 100 days of gestation.
Alkaloids affect the fetal brain and act as a sedative, causing the fetus to remain still. Legs and joints become stiff or fixed in abnormal locations. This may affect one or more joints or limbs and the spine.
“Most body structures are formed during early gestation,” explains Steffen. “The palate closes between 55 and 60 days of gestation. If the fetus is sedated by the alkaloids in lupine or another toxic plant at this point, the tongue isn’t moving and forms an obstruction as the palate plates move toward one another, preventing those plates from coming in from the sides and fusing.”
“We see similar defects caused by other plant toxins such as hemlock,” he continues. “Any kind of plant alkaloid or toxin can affect the nervous system, and some viruses can cause these abnormalities. In order for legs and joints to be mobile and develop normally, there must be an intact nervous system or there will be contractures as the muscles atrophy.”
“If there’s spina bifida, hydrocephalus or calves missing part of the brain, they often have stiff, crooked legs as a result. If there is no function and no motion during development, the joints become fixed,” Steffen says.
“Spina bifida calves can also create dystocia. In many of those calves, the hind legs are in fixed position, curled under the belly,” he says.
If joints cannot flex and move, there will be difficulty getting the calf extracted through the birth canal. Some hydrocephalic calves won’t fit through the birth canal because the forehead is too large.
Sometimes a normal fetus has an abnormal twin attached to the fetal membranes. This fetal abnormality is usually a mass of connective tissue with skin and hair. Other abnormalities include calves with two heads or extra legs.
Hormonal abnormalities can also cause birth problems. Hormones produced by the calf as it reaches full term are the signals which trigger onset of labor in the dam. In some instances, an abnormality in the fetus may interfere with appropriate signaling. “Labor isn’t triggered at the proper time and the fetus just gets bigger. Eventually labor is triggered, but the calf may then be too large for normal birth,” says Steffen.
Genetic defects
Certain malformations of the fetus are inherited, and many of these are simple recessive genes. The defective gene must come from both sire and dam in order for the defect to show up in the calf.
Double muscled calves are normal in most aspects except for excessive bulk of certain muscles, which makes it more difficult for these calves to be born. In Angus calves with arthrogryposis multiplex (AM), often called curly calf syndrome, legs are crooked and twisted in different directions.
“Whether or not this type of fetus can be delivered will vary with size of the calf,” shares Steffen. “Many arthrogryposis calves are small and one can usually manipulate the legs and get the calf out, though delivery will be harder with larger calves.”
Another inherited defect in Angus and Angus-cross cattle is contractural arachnodactyly, sometimes called fawn calf syndrome. Affected calves have skeletal abnormalities including a long, arched back, very short underline, long leg bones and long, weak pasterns. In some instances the skeletal and limb malformations may cause dystocia.
Calves with pulmonary hypoplasia anascara are generally large, heavy calves that can’t be delivered normally.
“Calves with pulmonary hypoplasia anascara don’t have proper lymph node structure, so their bodies fill with fluid. They are huge and heavy because of the fluid,” says Steffen.
Other inherited defects which sometimes cause dystocia include anchondroplastic or bulldog dwarfism and calves with edema in legs and head. Head and neck swelling can also be an effect of dystocia, as a result of being in the birth canal too long.
“Some big bulldog dwarf calves create a delivery problem because of their compact nature,” says Steffen.
Each breed has its own genetic problems.
“Some recessive defects hide in a carrier, and the cows don’t produce any affected calves because the stockman always uses an unrelated bull. This specific gene never gets doubled up,” Steffen says.
The majority of abnormalities he sees are not genetic.
“It pays to investigate the abnormalities to be sure so producers can keep using a bull or cow without worry. This can also bring peace of mind when marketing heifers by a certain bull and being confident the person who buys them won’t have problems,” he says.
Heather Smith Thomas is a corresponding writer for the Wyoming Livestock Roundup. Send comments on this article to roundup@wylr.net.
