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Evaluation of Bacterial Endophytes of Grass and Legume Forages as Emerging Causes of Reproductive Loss
Department of Veterinary Sciences
Pregnancy losses in livestock caused by infectious microoorganisms pose a serious and ever-present threat to the animal production agriculture of Kentucky and the nation. The single most frequent cause of late term abortions in livestock is infection of the placenta (placentitis). The proposed studies will extend preliminary investigations by experimental activities whose primary aim is to establish an etiologic relationship between bacterial endophytes of forages and placentitis-induced pregnancy losses in horses, cattle and goats.
2009 Project Description
Epidemiological studies in herbivores have shown that spikes in abortions occur after stresses to pasture forages, which include droughts, and frosts and freezes to lush high nitrogen pasture forages during the spring and fall. A spike in nitrate in the form of potassium nitrate in forages occurs during and after stress to pasture forages. In animals grazing these stressed forages, there is not only an increase in nitrate in the blood, but also elevated levels of ammonia.
Previous field studies during a spike in reproductive losses in mares and recently completed experimental studies have shown that during and after a spike in ammonia in the blood of animals, pregnant animals become susceptible to variety of reproductive disorders, including early fetal loss, mid and late term abortions and neonatal losses.
Elevated ammonia levels in the blood appear to be an important biomarker for subsequent immune suppression in animals. Ammonia is a potent immune suppressive agent in animals. It is suspected that the ammonia is causing immune suppression, thus allowing animals to become susceptible to a variety of opportunistic microorganisms, including the suspect causative agent for the fetal loss syndrome.
These findings are important as on-going field trials on affected farms with severe fetal and neonatal losses have shown that reducing the nitrogen levels in the diet of pregnant mares dramatically reduces fetal and neonatal losses.
A reproductive loss syndrome in herbivores, including horses appears to be associated with a microorganism that induces pathognomonic lesions in the amnion and amnionic umbilical cord of fetuses. In addition, a few adults with affected fetuses are likely susceptible to the same microorganism that has an affinity for the pericardial sac, epicardium, and the eye with lesions of unilateral endophthalmitis.
Numerous bacterial species have been isolated and evaluated from aborted fetuses, but none are consistently found in fetuses affected with the fetal loss syndrome. These bacteria are likely secondary opportunistic bacteria. Previous epidemiological studies and climatic conditions that are present when spikes in abortions occur suggest that the primary etiologic agent is likely a fungus, but in the past fungi were not consistently isolated from affected fetuses when conventional culture methods were used.
However, during the spring of 2009 while fetuses were affected with the fetal loss syndrome, alternative culture methods were utilized and a suspect etiologic agent was isolated from early, mid and late term fetuses that had clinical and pathologic lesions consistent with the fetal loss syndrome. Electron microscopic studies suggest that the agent seen in fetal tissues and the agent cultured in pure culture are the same agent. The suspect agent appears to be an obligate intracellular microorganism. It grows well in tissue culture cells and in chick embryos, but not in cell free media. It is suspected that the agent in nature may require a symbiotic relationship with microorganisms in soils and forages. The suspect causative agent is very minute and its morphologic characteristics, which appear to be fungal-like, can only be distinguished by electron microscopic examination. Genetic testing utilizing 16s ribosomal RNA also suggests that it is a fungus. The genetic sequence does not resemble any in the current database. It is suspected that the isolated suspect agent is a newly recognized fungus.
Our goal is to test this suspect causative agent in pregnant herbivores to determine if it is abortigenic with the same pathognomonic lesions seen in affected herbivores. The factors that predispose animals to the reproductive loss syndrome appear to be associated with the diet of herbivores. Also, affected animals appear to be affected with an immune suppression that allow opportunistic infections to occur. Ongoing studies on affected farms show that reducing the nitrogen in the diet of pregnant mares dramatically reduces fetal and neonatal losses.