Effect of experimental infection with ovine ureaplasma upon the development of uroliths in feedlot lambs.

Urinary calculi development in grain-fed lambs is a cause of serious economic loss to sheep producers in the USA. Rations containing sorghum grain and cottonseed meal, particularly, are calculogenic especially in those cases in which the calcium and phosphorus ratio is not balanced. The chemical composition of calculi taken from lambs is most often magnesium ammonium phosphate. Ureaplasmas have been isolated from the urinary tract of sheep with urinary calculi. These isolates, as well as certain other isolates of ovine ureaplasma, produce a sediment in aged cultures that is composed primarily of magnesium ammonium phosphate. In order to determine the relationship of ureaplasmal infections to the formation of calculi in the urinary tract, four treatment groups were established, comprising uninoculated-balanced ration, uninoculated-calculogenic ration, inoculated-balanced ration, and inoculated-calculogenic ration. As signs of calculosis developed, the wethers were necropsied and calculi collected and weighed. Also, culture material was obtained from four sites in the urinary tract and urine was collected for examination. A significant difference appeared in the number of lambs developing calculi between the calculogenic and noncalculogenic rations. No significant difference was evident in the total number of cases of urinary calculi in the inoculated compared with the uninoculated group. However, a very large difference in the total weight of calculi (15.4 g) was observed between the inoculated and uninoculated groups. Although the correct formulation of the ration is of prime importance in preventing urinary calculi formation in sheep, it is possible that ureaplasmal infections may influence the total amount of calculi produced and perhaps the physical characteristics of the calculi crystals.