Male castrated ruminants on grain rations are susceptible to urolithiasis leading to an inability to urinate, then perforation of the urethra or a ruptured bladder. Mortality is high in cases of complete obstruction and surgery would the only treatment. Therefore prevention is critical to reduce losses.
In a 600 lamb feedlot a new intake of approximately 200 lambs from at least 3 separate sources, were found to be dying sporadically after approximately 5-6 weeks in the feedlot. These crossbred lambs were aged from 4-7 months and had been run in a pasture on the farm for a month prior to being introduced into the feedlot.
On examination approximately 6 animals showed signs of illthrift, were tucked up appearance and stood on their own in the lot. On closer inspection, swelling in the ventral abdominal area was noted and in a few cases, a necrotic draining wound was found ventral to the body of the sheath. There was extensive ventral subcutaneous oedema when opening the abdominal cavity.
The necropsy revealed a thickened, red bladder, obvious ureters in most cases and enlarged, soft kidneys. On opening the bladder, a large volume of granular sand-like material could be felt and seen. On incising the penis along its length, areas of necrosis and haemorrhage were found along with more of the sand-like material in the lumen.
Chemical evaluation of the calculi in this instance was 48% calcium oxalate and 52% ammonium phosphate.
Grain diets have a number of potential effects on the urine. High grain rations are phosphorus rich so that urinary phosphorus levels also increase thereby providing more phosphorus solutes in the urine.Rapid introduction to grain rations has the potential to reduce overall urine volume, thereby concentrating the urine (and its solutes) even further. This is particularly the case when grain is fed in a few large meals which has an effect on kidney function. This is a short term change but it may allow the initial development of the crystals to form. A heavy grain ration will also increase the mucopolysaccharide fraction of the urine which acts as a cement for the calculi. These mucoproteins favour the formation of calculi when precipitates are already present. This mucoprotein content appears to increase on heavy concentrate-low roughage rations and can also be influenced by pelleting the ration. Feedlot rations are known to provide high mineral feeding levels and rapid growth rates appear to be the association to the high levels of mucoprotein in the urine in animals fed these diets. Thus urolithiasis is a common problem in feedlotted steers and wethers.
These lambs, presumably stressed and in store condition on arrival had to adjust to the new groups in the introductory paddock before being introduced into the feedlot ration. This may have contributed to a reduced water intake. They were given access to ad lib grain in feeders and lucerne hay. Following the increased number of urolithiasis cases the ration was reformulated to contain a more precise 2:1 Ca: P ratio with 0.5% NH4Cl and 1% NaCl. Also for a few weeks after diagnosis, until the ration could be reformulated, free salt licks were provided to the pens.
At the time of writing, cases had reduced for a few months but began to appear again and continue to be a problem. Subsequent testing of the calculi showed that the calcium carbonate components had been corrected but 100% ammonium phosphate calculi continued to be a problem. The salt content was increased to 4% to try to increase fluid intake and provide a flushing action in the urine, despite the risk of reduced feed intake with such a high salt component. The producer eventually sold the property without satisfactorily controlling losses due to urolithiasis.