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Abnormalities That May Impede The Birth Process

Occasionally the stockman encounters a diffi cult calving situation caused by an abnormality in the fetus or dam. As stated by Dr. David Steffen, diagnostic pathologist and professor, School of Veterinary Medicine, University of Nebraska, the most common problem is discrepancy between size of the calf and pelvic area of the dam. This type of calving problem can be eliminated or minimized by using bulls that sire calves small to moderate size at birth and making sure heifers are well grown, with adequate pelvic area.

Other problems are less simple. When checking a cow or heifer that’s not progressing in labour, keep in mind the possibility of an abnormality. There may be unusual circumstances in which positional adjustments will still not allow delivery. Some situations may be due to a congenital (present at birth) or genetic (inherited) defect in the calf or an abnormality in the dam that may be hindering birth progress or making it impossible for the calf’s legs to be repositioned to allow delivery.

CONGENITAL DEFECTS

“Defects in the fetus that may cause dystocia are usually attributed to those causing dramatic effects on the muscular or skeletal systems,” says Steffen. Some congenital defects are due to accidents in fetal development. Others are caused by teratogens. Teratogens are defined as any factors that cause 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 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 the main factors that determine the outcome, and whether a teratogen will produce a birth defect. The higher the dose, the longer the period of exposure, and the time of gestation will be key factors,” explains Steffen.

“One of the most disturbing syndromes is schistosoma reflexus,” says Steffen. “The 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 internal organs.

“When you reach into the cow to try to determine what’s holding up progress, you find all four feet presented, and may get a handful of intestines. You may suspect the uterus is ruptured and think 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. Schistosomus calves from purebred cattle should be sampled and reported.

Lupine calves are another instance in which the fetus is malformed. Usually it’s the leg joints and limbs, but occasionally you’ll 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, but you can usually deliver these calves through the birth canal — unless the deformity is severe.

These defects 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 doesn’t move enough. Legs and 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. 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 around and forms a physical obstruction as the palate plates move toward one another. The tongue is in the way and prevents those plates from coming in from the sides and fusing,” explains Steffen.

“We see similar defects caused by other plant toxins such as hemlock. 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. Anything distal to that injury will contract as the muscles atrophy,” he says.

“If there’s spina bifida, hydrocephalus, or calves are missing a large part of the brain, they often have stiff, crooked legs as a result. If there is no function, no motion during development, the joints tend to 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. In many of those calves the hind legs are infixed position, curled underneath the belly,” he says. Any time the joints cannot flex and move there will be 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 that may hinder birth 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 instances the fetus may have an abnormality that interferes with appropriate signalling. “Labour isn’t triggered at the proper time and the fetus just gets bigger. Eventually it triggers, but the calf may then be too large for normal birth. At times we’ve seen giant calves in embryo transfer programs. I don’t know if anyone has figured out why, but it may be an abnormality in the signalling between the embryo and the cow. I’ve seen some monster-size fetuses that were otherwise normal, but huge,” he says.

GENETIC DEFECTS

Certain malformations of the fetus are inherited, and many of these are simple recessives. 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. This is an inherited trait in certain breeds.

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. Many arthrogryposis calves are small and even though there’s a dystocia you can usually manipulate the legs and get the calf out. With the larger ones, it can be a problem.”

Another inherited defect in Angus and Angus-cross cattle is Contractural Arachnodactyly (CA), formerly called Fawn Calf Syndrome. A University of Illinois research team recently identified the mutated gene causing this defect, which is inherited as a simple recessive. Affected calves have skeletal abnormalities that include a long, arched back, with very short underline and long leg bones (elbows and stifles may be almost touching, beneath the belly), and long, weak pasterns. Even though some of these calves are unable to stand without help at first, many do survive. In some instances the skeletal/limb malformations may cause dystocia.

Calves with Pulmonary Hypoplasia Anascara (PHA) have been seen in Maine Anjou and Shorthorn cattle. “These are generally large, heavy calves that can’t be delivered normally. They don’t have proper lymph node structure, so their bodies fill with fluid. They are huge and heavy because of all that fluid,” says Steffen.

Other inherited defects that sometimes cause dystocia include anchondroplastic or bulldog dwarfism, and calves with edema (fluid/swelling) in legs and head (sometimes seen in Ayrshires). Head and neck swelling can also be an effect of dystocia, however — the result of being in the birth canal too long. “Some big bulldog dwarf calves can create a delivery problem because of their compact nature,” says Steffen.

“Some bulldog dwarf calves also have cleft palates. The head, back and legs are too short, yet they still have full muscle mass. The tongue is still full size but the head is short, so during development the tongue gets in the way and the palate plates can’t get closed and fused like they should,” he says.

Each breed has its own genetic problems. “Some recessive defects hide in a carrier cow line for a long time and the cows don’t produce any affected calves because the stockman is always using an unrelated, clean bull, and that specific gene never gets doubled up. Eventually, however, someone produces a good bull by a son or grandson of one of those carrier cows and if that bull gets line bred or into an AI stud, pretty soon the gene frequency is high enough that it will be noticed,” he says.

Most conscientious producers try to learn enough about their cattle to avoid problems, if possible. “If a breeder has an abnormal calf, I encourage them to contact their breed association, if it’s a purebred herd, or even if it’s a crossbred and you know the sire. When breeders try to keep defects quiet, it just delays solutions and it all blows up a year or two later,” he says.

The majority of cases he sees are not genetic. “It pays to investigate them, however, and be sure of that affirmation, as it allows you to keep using that bull and cow without worry, or to market heifers by that bull and be confident that the person who buys them won’t have problems,” he says.

ABNORMALITIES IN THE DAM

The most common problem on the maternal side is a too-small pelvis for delivery of a too-big calf, but sometimes there are structural or hormonal abnormalities in the dam that would hinder birth.

Occasionally a heifer has an unusual situation or defect that will not allow for ease of birth. For instance, an abnormal bony protrusion at the top of her pelvis might not allow the calf’s head to fit through.

“There was a genetic problem in Jersey cattle, reported 20 or more years ago, called recto-vaginal constriction,” says Steffen. “Connective tissue around the rectum and vagina was less elastic than normal, resulting in severe dystocia. The constriction could be so extreme that it would be nearly impossible to put a hand and arm into the rectum to do a palpation. Those heifers had to be culled,” he says.

In any breed, sometimes there are instances in which hormone signals don’t work properly at parturition and the cervix may not dilate. Oxytocin release and progesterone changes are necessary for relaxation, preparing the birth canal for passage of the fetus. If something goes wrong with these hormonal signals it may be impossible to deliver the calf normally.

“Nutritional status of the dam can play a role as well, especially calcium levels in heifers — to generate the muscle contractions that assist in pushing the calf out. If calcium is marginal and the calf is big, or it’s a young heifer that has never been dilated before, and she starts straining hard, she becomes exhausted more quickly and it may be difficult to get the calf out,” explains Steffen.

The key to resolving most problems is watching cows closely at calving, knowing when they are due, and giving early intervention if there is a problem. If a person can detect a problem early and assist — even if the calf must be removed by C-section or a fetotomy — you’ll end up with a live cow, even if the fetus is too abnormal to save.

“Often cows do better (and may have a reproductive future) with a clean C-section than with a fetotomy or forced extraction. You can do more damage to the pelvic canal with the latter situations. With a clean surgical incision you can get the calf out without stressing the cow or heifer,” says Steffen.

“I had a classmate compare post-delivery performance of heifers that came into feedlots bred. He found that C-section heifers returned to feed and gained weight faster than the hard pulls. If you pull a big (or malformed) calf out through the pelvic canal, you crush a lot of tissue and may separate the pelvis. This tissue damage may take longer to heal; you cause a lot more injury, even though it doesn’t bleed.” There can be less trauma to the cow with a C-section.

Hydroallontois (excess fluid in the outer water sac) or hydramnios (extra fluid in the amnion sac surrounding the calf) are rare conditions that hinder normal birth. The calf itself is often abnormal and may be small for its stage of gestation, but the cow develops a huge belly due to extra fluid. Many of these cows cannot make it to term because they have trouble getting up and down. The cow may become weak because there isn’t room for much food in her gut, and the huge uterus puts pressure on her digestive tract and lungs. If a cow does survive till term, she will need help to calve because her uterus is so distended she cannot push, and her cervix may not dilate.

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