Non-infectious newborn calf problems and survival (Proceedings)
National survey data concerning dairy calf health and survival have shown very substantial death rates over the last 10 to 15 years. The National Animal Health Monitoring System reports the number of unweaned dairy heifer calf deaths as a percentage of calves born alive to have varied from about 7.8% to 10.8 % between 1991 and 2007. Most of the causes of death reported by producers are infectious diseases, the most common being scours/diarrhea and respiratory problems. Because infectious diseases are the most prevalent calf health problems between birth and weaning, veterinarians and other dairy health advisors have placed considerable emphasis on vaccination strategies and colostrum administration as key features of calf management.
Compared with infectious disease reporting, much less emphasis has been placed on stillbirth as a cause of calf death. Death losses at delivery, or within the first 2 days after delivery, which is the commonly used definition of stillbirth in the dairy industry, are rarely the result of infectious disease. These deaths typically result from physiological derangements of newborns during delivery or during adaptation to life outside the uterus. Although these losses are less carefully tracked in the industry, current reports suggest stillbirth rates between 6 and 12%, and the NAHMS Dairy 2007 survey reports 14% stillbirth and death before 48 hrs. Therefore these losses are nearly as common or more common than infectious disease in causing calf death. While there are numerous potential causes of stillbirth, including genetic and nutritional problems, dystocia is the single most common predisposing cause of stillbirth.
Dystocia delivery is not only responsible for dramatically increasing the likelihood of stillbirth, but also increases the risk for subsequent calf health problems. By disturbing adaptation to extra-uterine life, dystocia impairs normal physiological functions, increases the risk of poor colostral transfer and decreases resistance to infectious pathogens, therefore increasing infectious disease likelihood.For a calf management program, the day of delivery is the single most critical time. Although dystocia cannot be eliminated, its' effects on the cow and the calf can be mitigated by proper management and decision-making. Calves from dystocia delivery, plus calves born without dystocia that are slow in adaptation, can be identified and managed to increase their survival. Colostrum management and appropriate calf biosecurity measures also need to occur in this critical first day. If optimum calf health is the goal, all of the observations, decisions and actions involved in delivery and the first day of a newborn calf's life should be performed by well trained workers who are educated about the importance of their work to the long-term health of the calf.
Adaptation to extrauterine life – physiological calf problems
Birth is the most dramatic transition that an animal ever makes. The birthing process itself is attended by the trauma and stress of delivery and a period of anoxia/asphyxia, all of which may be exaggerated in the event of dystocia. In addition, the newborn must adapt to its extrauterine environment. During this process, virtually every organ system and every metabolic process is affected. Within just a few minutes of time, the neonate must exchange its own respiratory gases, remove its own waste products, generate heat and thermoregulate, alter and regulate its blood flow and, in the case of an ungulate, it must also fairly shortly begin to ambulate and seek its own food source.
Each aspect of this adaptive process is inter-related and dependent on the others. For example, heat generation can be accomplished through several mechanisms including nonshivering thermogenesis, shivering thermogenesis, and the metabolic heat of muscular activity. Each of these, however, depends on other physiological activities such as normal oxygenated blood flow to the appropriate tissues, normal supply of metabolites and homeostatic control of acid base parameters, normal neuromuscular function, and behavioral drive to become active and stand, etc. With this example alone, it should not be surprising that one of the most commonly documented neonatal problems is hypothermia.
Most neonatal problems show relatively subtle and nonspecific disease signs, and it is difficult to specifically identify one organ system or another as more significantly affected by disease. Typical clinical signs in the newborn calf include inactivity, weakness, slowness in developing normal behavioral responses such as attempting to rise or nurse, variable body temperature, and variable heart and respiratory rates. Furthermore, it is typical even for severely compromised calves to look relatively normal for the first 15 to 30 minutes after delivery while the catecholamine surge is still in effect, but then to gradually become weaker and less responsive as time goes on. In cases of dystocia, it is easy to conclude that the inciting problem is prolonged birth asphyxia. Because delivery is the primary focus in most dystocias, the process is considered successful when a live calf is born, and careful assessment of the calf is often forgotten. There is a strong tendency to assume calves will survive and perform normally, and no specific treatment or monitoring are initiated.
Commonly, problems in calves following dystocia are detected long after the optimal time to address them, and the fact that the problems are associated with dystocia goes unrecognized. Better health can be achieved in dystocia affected calves if a routine monitoring system is followed and supportive care is provided before problems develop. Neonatal calves are remarkably resilient and usually capable of making the needed physiological adjustments if sufficient care and time are provided.
The most important first step in improving survival and health of calves following dystocia, is recognizing that all such calves are compromised by the dystocia event. Most commonly, the calf is cursorily evaluated after birth. Only those that are severely and obviously affected usually receive additional care. Even those that seem relatively unaffected, however, have sustained a physiologic challenge that warrants attention. Typically a modest level of nursing care, with minimal cost or additional medical intervention, is adequate to ensure improved performance of the calf.