PIC Update: May 2011

Sometimes a research project takes us down an unexpected path of discovery. The original question is answered, new questions arise and, if we are lucky, new and unexpected information comes to light. Dr. Andrew Olkowski of the University of Saskatchewan has been studying various causes of heart failure in broilers for years, and has most recently looked into the link between shell quality and heart failure. In doing so, he has uncovered a fascinating, but problematic, link between shell quality, hen status and some never-before-seen anomalies in broiler embryos.

Recent advances in the understanding of risk factors associated with predisposition to heart disease in humans have linked several important maternal factors with heart failure in some individuals. It has been shown that heart disease may be initiated in utero, and heart failure may be triggered by precipitating factors later in life. In essence, there are a number of similarities in many aspects of pathology, clinical symptoms, hemodynamic changes and biochemistry of heart failure in humans and broiler chickens. Therefore, many similar maternal risk factors may be as relevant in broiler heart failure etiology as they are in human heart etiology.

For birds, the eggshell is an important component of the interface between the embryo and the external environment. Therefore, changes in eggshell characteristics can have a profound effect on the physiological processes of the developing embryo. Because of this, and given what we know about human heart health, Olkowski felt it was important to consider that the cardiac health of broiler chickens may be affected by factors associated with eggshell characteristics during embryonic life. He and his research team began this project by investigating whether eggshell quality may be a factor increasing the predisposition of broilers to develop acute or chronic heart failure.

However, the first round of experiments led to the discovery of several important, previously unrecognized factors that may help us in understanding the etiology of not only heart failure, but also many other problems commonly seen in commercial broiler operations. The findings obtained from these experiments indicated that poor eggshell quality was associated with overall reproductive and hatchability failure as well as many common health problems seen in broiler flocks. The higher incidence of these conditions seemed to be independently correlated to aging of the parental flock, as well as negative attributes of eggshell quality. Therefore, a new approach and broader experiment was designed to look at these things, specifically targeting aging breeder flocks.

Ten thousand commercial broiler eggs were collected from a breeder flock at 62 weeks and the condition of the eggshell matrix was examined using light. Eggs were separated into two general categories: 1) eggs with normal eggshell – low risk, and 2) eggs with poor quality eggshell – high risk. From the pool of 10,000 eggs, 65.5 per cent were classified as low risk, and 26.3 per cent were classified as high-risk.

All eggs were then incubated and hatched according to routine procedures in commercial production. All good-quality chicks, hatched from eggs representing both groups, were raised as commercial broilers. Daily monitoring recorded mortality, morbidity, and overt signs of heart failure and ascites. All mortalities and birds euthanized for humane reasons were subjected to detailed post mortem examination. Condemnation data was collected for each group separately. A total of 683 unhatched eggs from the low-risk group, and 720 unhatched eggs from the high-risk group were subjected to detailed examination in order to determine the causes of reproductive failure. Broilers hatched from the high-risk group showed lower growth rate and substantially higher losses associated with mortality, morbidity and condemnations than those in the low-risk group. Acute heart failure (sudden death syndrome) and chronic heart failure (ascites) accounted for the majority of losses in both groups, but the incidence was much higher in the high-risk group that had poor quality eggshells. These results were somewhat suspected and further confirmed Olkowski’s earlier findings of a link here. A major cause of morbidity was leg problems, and major causes of condemnations included cellulitis and cyanosis, all associated with inferior eggshells.

One of the most interesting overall findings of significance was what they found in the unhatched eggs: a high incidence of monstrosities in near-term embryos. The most common deformities included hydrocephalus, exposed brain, lack of eyes, a single eye, deformed beak, lack of upper beak, deformed legs and exposed body cavities. In many instances, embryos were affected by multiple deformities. Some of these cases attracted special attention because of their unusual presentation, complex nature and novelty – particularly spina bifida and incarceration of the intestinal loops. These embryonic defects were previously not observed in broilers.

Previous literature suggests that spina bifida in chickens is extremely rare. However, the detection of this deformity in relatively large numbers of broiler embryos may signify a more serious and widespread problem, which therefore requires further investigation. The researchers are unsure of the causative factors of spina bifida, but nutrition, toxicology and genetics could all play a role, as does hen status. Undoubtedly, metabolic status of the hen has a very significant impact on the health and performance of the offspring. The high incidence of embryo deformities in general is likely a sign of a more profound problem, and in this context the importance of these findings should be evaluated very seriously.

Overall, the findings of this project not only advanced our knowledge considerably, but also provided several important facts of practical significance. As such, the findings should set new trends in the research strategy. In order to develop management strategies for more effective control of the most common causes of significant economic losses in the Canadian broiler industry, such as sudden death syndrome, ascites, cyanosis, and cellulitis, identification of parental risk factors that may predispose broilers to health problems is essential. To read more about this project, please visit www.poultryindustrycouncil.ca.

written by Kimberly Sheppard, Research Co-ordinator