Occasionally a difficult calving is caused by abnormality in the fetus. David Steffen, a diagnostic pathologist at the University of Nebraska, says that whenever you’re checking a cow or heifer that’s not making progress in labour, keep in mind the possibility of congenital abnormality. Some congenital defects in the calf may hinder the birth progress or make it impossible for the calf’s legs to be repositioned to allow delivery.
“Defects in the fetus that may cause dystocia include adverse effects on the muscular or skeletal systems,” says Steffen. Some are due to accidents in fetal development. Others are caused by teratogens — a term that refers to factors that cause an abnormality in a developing embryo or fetus. Teratogens include drugs, hormones, chemicals, viruses, toxic plants, high body temperature, etc. Some of the resulting abnormalities may cause dystocia.
Many things influence embryonic and fetal development. Vulnerability varies at different stages of gestation. Each organ and structure has a critical period during which it can be altered by harmful external influences. Many organs are susceptible quite early in the embryonic stage, but the heart, cerebellum and urinary tract that develop later in gestation are vulnerable in later stages.
“Dose, duration and timing are factors that determine the outcome, and whether a teratogen will produce a birth defect,” says Steffen. “The higher the dose, the longer the period of exposure, and the time of gestation are key factors.” Skeletal abnormalities may hinder passage of the fetus through the birth canal.
“One of the most disturbing syndromes you might encounter is schistosoma reflexus,” says Steffen. “The fetal spine is U-shaped and the top of the tail is close to the head, and the fetus is turned inside out.” The chest and abdomen are incompletely formed, exposing the internal organs.
“When you reach into the cow to assist or to determine what’s holding up progress, you will find all four feet, and may get a handful of intestines. You may at first 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 by fetotomy (cutting the fetus into pieces) or C-section.
Lupine calves (resulting from cows eating the toxic plant) are another example in which the fetus is malformed. Usually it’s the leg joints and limbs and spine, but occasionally you’ll see one with a cleft palate. Often the legs are crooked or the joints are fused and fixed so the legs don’t move properly, but you can often deliver these calves through the birth canal — unless the deformity is too severe.
These defects in lupine calves are caused by certain alkaloids, if the cow eats lupine between 40 and 70 days’ gestation. The alkaloids affect the brain and act as a sedative, and the fetus isn’t moving much. The joints become stiff or fixed in abnormal locations. This may affect one or more joints or limbs, or the spine.
“Most body structures are formed during early gestation,” says Steffen. The palate closes at about 55-60 days of gestation. If the fetus is affected by lupine or another toxic plant alkaloid at that point, the tongue isn’t moving and therefore forms a physical obstruction as the palate plates move in toward one another. When the tongue is in the way and prevents those plates from coming in from the sides and fusing, the insult occurred prior to 60 days.
Similar defects can be caused by other plant toxins, such as hemlock. Any plant alkaloid or toxin can affect the nervous system, and even some viruses can cause these abnormalities. In order for the legs and joints to be mobile and develop normally there must be an intact nervous system — anatomically and functionally. Similar to a person having a spinal injury or a nerve injury in the arm or leg, any area beyond that injury will contract as the muscles atrophy.
If there’s spina bifida, hydrocephalus, or calves missing a large part of the brain, they will often have stiff, crooked legs as a result, he says. If there is no function, no motion during development, the joints become fixed.
Some hydrocephalic calves will not fit through the birth canal because the forehead is too large. “Spina bifida calves can also create dystocia,” says Steffen. “In many of those calves the hind legs are in fixed position, curled up underneath the belly.” If the joints cannot flex, bend and move there will be more difficulty getting the calf extracted through the birth canal.
Sometimes a normal fetus has an abnormal twin attached to the fetal membranes. This fetal “monster” 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 that trigger onset of parturition in the dam. In some instance the fetus may have an abnormality that interferes with appropriate signalling and this does not occur. “Labour isn’t triggered at the proper time and the fetus just gets bigger and bigger,” says Steffen. “Eventually it triggers, but the calf may then be too large for normal birth.”