A batch of 272 first cross lambs had fed in a farm feedlot near Fifield in central western NSW for 7 weeks when deaths from urolithiasis were first observed. Four weeks later 24 lambs had died (although some may have been from other causes). The owner noticed that the lambs were swollen along the prepuce and inguinal area before death. The lambs had been grazing in a small paddock with trees and were watered from a farm dam. The lambs had access to pellets from a self-feeder and wheat straw.
On the 22nd June 2005, I was called to investigate the mortality and suggest preventive options. I examined two crossbred wether lambs that both had marked swelling of the inguinal area and prepuce. On post-mortem both lambs had ruptured urethras with pools of urine contained in necrotic tissue cavities. One lamb had more than 50 small pale smooth un-layered stones of 1 to 8x6x5 mm diameter in its bladder. These were mainly Magnesium Ammonium Phosphate stones.
The pellets fed to the lambs were based on wheat (45%) and also contained 24% millrun (bran and pollard) and 20% dried distiller’s grain. In addition the pellets contained 3% fine ground limestone, 0.13% dicalcium phosphate, 0.8% salt, 1% sodium bicarbonate 1.3% bentonite plus Molaphos gold, a ruminant pre-mix and 2.2% oil (as fed). The ration had a protein content of 16.9%, ash of 9.0%, calcium of 1.4% and phosphorus of 0.67% (on a dry matter basis). The water in the farm dam looked and smelled acceptable and so was not tested.
I recommended that the owner sell the remaining wether lambs especially those that were close to finishing weight. I also recommended that the owner feed a ration with a lower total mineral content that would acidify the urine, ensure a Ca:P ratio of about 2:1 and increase water intake. As the owner also owned the plant that manufactured the pellets I recommended to his nutritionist that for feedlot lambs he increase the salt content of the pellets to 2%, add 0.05% ammonium chloride, remove the sodium bicarbonate (despite its beneficial effect in preventing acidosis), lower the amount of lime from 3.0 to 1.5% and remove the dicalcium phosphate. I also recommended that the lambs have access to dietary roughage and good quality water at all times.
Fortunately, rain fell in mid June with follow up rain in July. Good pasture growth rendered the feedlot redundant.