Dystocia can be defined as a difficult or abnormal calving due to a prolonged, unassisted birth or due to a prolonged and/or severe assisted calf delivery. Factors known to cause dystocia include pelvic size of the dam, calf size, calf presentation (for example, backwards or head turned back), and maternal factors including weak labor, insufficient dilation of the cervix and uterine twist or torsion. The most common cause is a mismatch in dam pelvic size and calf weight, often seen in heifers delivering large bull calves. Inappropriate timing of human intervention or excessive force applied during delivery may cause additional fetal trauma, stress and even stillbirth. Following dystocia, a calf is 6 times more likely to get sick than a calf born normally, with 69% of all deaths between birth and weaning occurring within 96 hours of birth.
The key event in the transition from life inside the uterus to an independent existence is the initiation of breathing so the lungs become inflated and the blood oxygenated. The first breath is the hardest to take-similar to the first hard push of air necessary when inflating a balloon. In order to facilitate this process after a dystocia, immediately after delivery (within 30 seconds), the calf should be placed upright on its sternum (breastbone) to maximize ventilation. Calves should have their upper respiratory tract (nose and mouth) cleared of any fluid or other physical obstruction, either by hand or suction bulb. Calves should never be hung by their rear legs for more than 90 seconds or swung around by their back legs to remove fluids by gravity flow. Instead these procedures have been proven to increase pressure within the chest cavity, making it much more difficult to expand the lungs. Calves should make active respiratory movements within 30 seconds of being delivered.
If spontaneous breathing does not begin, it is imperative to establish an airway and stimulate respiration. Many methods have been tried but very little published information is available as to their efficacy. Once the calf is placed on its sternum, vigorous stimulation of the calf by rubbing around the head or body and placing a finger or piece of straw in the nose should initiate a gasping reflex that helps aerate the lungs. Pouring cold water over the calf's head or down the ear has also been used with some success to stimulate respiration. Mouth-to-mouth or mouth-to-nose resuscitation is commonly tried but very difficult to do effectively. Establishing a tight seal to prevent air leakage is difficult but, even more importantly, the air blown in has a tendency to go down the esophagus and fill the stomach which makes breathing more difficult for the struggling calf. To avoid these problems, a veterinarian may use a cuffed endotracheal tube to provide positive pressure ventilation effectively. Certain prescription medications such as doxapram may also be used to stimulate respiration although severely affected calves do not seem responsive to it. Veterinarians may also choose to use buffer therapy with injectable sodium bicarbonate to correct metabolic acidosis, a condition that often occurs following dystocia in which the calf's blood is more acidic than it should be. In general, cardiac resuscitation is not attempted in calves born without a heartbeat due to very poor chance of survival. Similarly, calves that do not respond to respiratory stimulation techniques and cannot sit up on their own after 10 minutes generally do not survive.
In moving from the uterus to the outside environment, baby calves experience a dramatic shift in temperature. Calves delivered normally maintain their body temperature (thermoregulation) by shivering and by mobilizing energy from brown adipose (fat) tissue. Simple, natural physical activity such as standing, walking, and consuming colostrum will also generate body heat. Following dystocia, calves have an impaired response to cold temperatures. Inadequate oxygen can reduce muscle tone and prevent shivering as well as decrease the calf's ability to utilize its brown fat. Calves with thermal stress and low vitality are slow to stand and nurse, limiting their ability to warm themselves through this natural physical behavior. These calves should be exposed to an infrared heater to improve rectal temperature, blood oxygen level, and respiratory rate. If electric heating pads are used, they must be closely monitored because they can get hot enough to cause burns, particularly if the calf is unable to move off the pad. Heat lamps must also be monitored to prevent burns.
Of course the single most important factor in calf survival is that it receives and absorbs adequate colostrum. It is essential that all calves receive 3-4 quarts of colostrum within the first 6 hours of life. Consumption of colostrum by calves in fetal distress has been found to be reduced by up to 74% in the first 12 hours of life. Since a calf is unlikely to voluntarily suckle after dystocia, it is recommended to feed colostrum via stomach tube ("esophageal feeder") within one hour of birth if there is any doubt as to the calf's vitality. Colostrum contains immunoglobulins that form the calf's immune system as well as nutrients vital to the newborn such as fat-soluble vitamins and sugars. Dystocia resulting in a weak newborn calf is a major cause of failure of passive transfer (FPT) due to low volume and delayed consumption of colostrum. FPT is known to increase susceptibility to infectious disease, increase neonatal sickness and death as well as result in long-term decreases in productivity (such as lower average daily gain) if the calf survives.
Other problems may arise due to complicated deliveries. Calves that are wedged in the pelvic canal for prolonged periods may be born with a swollen head and/or tongue. This condition will usually resolve itself within one to two days but feeding the calf with a stomach tube is required since the calf cannot suckle. Dystocias may result in trauma such as fractures of the legs, ribs and spine and luxations of the hip and spine. The extent of these injuries may not be obvious at birth but will become apparent over the next one to two weeks. The umbilicus (or "navel") may become infected due to prolonged contact with the ground, predisposing the calf to septicemia or "navel ill". Mild antiseptics should be used on the cord but avoid strong, caustic agents as these will cause irritation and inflammation of these sensitive tissues. Maintaining a clean, dry umbilicus and ensuring adequate high-quality colostrum ingestion are the best ways to prevent disease in newborns.
In summary, success in saving a calf after dystocia will depend largely on the condition of the calf at birth. Some will suffer major trauma during delivery resulting in severe bruising, fractured ribs, bleeding in the central nervous system, and other maladies resulting in death irrespective of treatment. Other calves will be born with a heartbeat but not breathing; these calves are good candidates for resuscitation. Establishing a patent airway, initiating breathing, and establishing adequate circulation are the cornerstones to immediate calf survival. However, early and adequate colostrum intake is essential for passive transfer of immunoglobulins, energy, thermoregulation, and long-term survival.