Resuscitation and critical care of neonatal calves (Proceedings)
Adequate resuscitation of the newborn is critical to decreasing calf losses in both beef and dairy herds. Despite the importance, there is little critically evaluated data available to aid in protocol development. Establishing a patent airway, initiating breathing, and establishing adequate circulation are the cornerstones to resuscitation in any species. In cattle post-dystocia resuscitation of the neonate focuses on establishing breathing and correction of acid base abnormalities. Additional attention may be required to address specific ailments that occur during calving, maintaining appropriate body temperature, and ensuring adequate colostral intake.
Rupture of the umbilical cord initiates hypoxia. Decreased oxygen tension and increased carbon dioxide concentrations stimulate gasping reflexes with subsequent aeration of the lungs. Increased oxygen tension in the blood and increased peripheral vascular resistance initiates closure of the ductus arteriosus, foramen ovale, and ductus venosus preparing the neonatal cardiovascular system for extra uterine life. If dystocia is prolonged and a substantial hypercarbia or acidosis develops prior to expulsion of the fetus, central nervous system depression may be severe enough to impair the reflexes that initiate respiration.
Removal of fluid from the pulmonary system is critical for normal aeration and oxygenation of blood. Some fluid is eliminated from the body during the birthing process. However, the vast majority is reabsorbed across the alveolar walls into the interstitium rapidly upon the initiation of respiration. Complete absorption of pulmonary interstitial generally occurs within several hours postpartum. After delivery a clear airway should be ensured. Recent data suggests that the practice of hanging calves to expel fetal fluids is unnecessary and placing them in sternal recumbency should allow for normal oxygen exchange and fetal fluid resorption.There are many methods that have been advocated for establishing respiration and airway patency in calves. Rubbing calves with bedding or towels is an attempt to stimulate the phrenic nerve. Placing a finger, piece of straw, or other implement in the nose will initiate a gasping reflex and help aerate the lungs. The use of acupuncture points on the muzzle has been advocated. Pouring cold water over the calf's head or ear has been advocated for stimulation of hypothermal respiratory stimulation. In addition to these methods positive pressure ventilation can be used to establish respiration. Many of these methods are practiced on a regular basis. However, very little information is available as to their efficacy in calves. Pharmacologic initiation of respiration is often attempted with the use of doxapram hydrochloride. This may have efficacy in mildly hypercarbic animals, but it is unlikely that severely affected animals will have a response. Reversal agents may be used if the dam was sedated during parturition with xylazine.
Cardiac resuscitation is rarely undertaken in ruminants as the likelihood of survival is less than 50% if resuscitation is begun prior to the start of a nonperfusing rhythm and less than 10% is started after asystole.
In addition to basic life support, care should be addressed to any trauma sustained to the calf during calving or as a result of prolonged dystocia. Fractures and crush injuries may be sustained during hard pulls using implements such as chains and fetal extractors. Calves with prolonged time in the pelvic canal may suffer from regional swelling secondary to poor venous return. Extraction of the fetus will reestablish venous drainage and subsequent reduction in the swelling over the next few days. Furosemide or mannitol may speed the removal of edema in severely affected individuals. Fractures and luxations may be treatable with reduction ad casting or splinting techniques.
In particularly harsh environments or after prolonged dystocia care should be taken to ensure normal thermal adaptation to extra uterine life. Rapid declines in body temperature and a failure of thermostatic regulatory mechanisms to completely restore normal rectal temperatures are characteristic of calves born to severe dystocia. Moderate to severe metabolic disturbances also mirror the changes seen in body temperature. This highlights the need to ensure that adequate body temperature is maintained in neonates. A recent study revealed that calves exposed to an infrared heater for 24 hours postpartum had significantly improved rectal temperature, arterial hemoglobin oxygen saturation, tidal volume, dynamic lung compliance, and respiratory rates that control calves. The authors postulated that the lower energy expenditures required for thermogenesis in these calves allowed for the increased energy demands required for the increased respiratory work needed to generate the changes in the respiratory parameters.
In addition to these vital parameters, ensuring adequate colostrum intake is critical to the long term health and immunologic stability of the calf. The ingestion and absorption of maternally derived colostral components plays a large role in the immunologic capability of the neonate. Bovine colostrum contains many substances that support immune function in the neonatal calf. Immunoglobulins are the most commonly studied molecules, but maternal derived immune cells, complement factors, lactoferrin, insulin like growth factor – 1, transforming growth factor, interleukin 2, and other soluble factors are present. In addition to immune support colostrum is an excellent source of nutrients vital to the survival of the newborn including sugars and fat soluble vitamins.