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Nitrate Poisoning

Ian Masters, District Veterinarian, Narrendera RLPB

Posted Flock & Herd February 2011

Two cases worth commenting on

1. Loss of 30 yearling beef animals at a local abattoir after feeding out millet hay in holding paddocks.

2. Sudden death of 260 merino wethers on the TSR near Hillston after grazing on wild sage (Salvia verbenaca).

In the fist case an irrigated millet crop had been used for grazing over the summer months. It was top dressed with a nitrogenous fertiliser in March and cut for hay in early April. Yearlings being held in bare holding yards over the weekend were fed on this hay on Friday afternoon. When they were checked on Saturday morning 30 had died.

PM was typical of nitrate poisoning. Dark chocolate coloured blood, inflammation of the abomasum and small intestines. Samples of the hay and rumen contents were positive for nitrate.

The second case involved a mob of sheep travelling on the TSR between Willanthry and Hillston. The drover in charge of the mob was a bit slack and had a habit of clearing out on weekends when he thought he could get away with it. The district was drought affected at the time and he locked them up on a bare Reserve and went home to Condobolin. By Monday morning the sheep would have been very hungry when they were let out on the road. Wild sage was about the only green plant growing on the recently graded table drains. It is a reasonably common plant on the side of the roads in this area and is usually avoided by stock. Sheep started to die late on Monday afternoon after the drover locked them up in a laneway. By the next morning 260 had died.

PM was not typical with most of the sheep opened up having bright red blood. All had very strong, aromatic rumen contents. The lining of the abomasum was inflamed as were the small intestines and there were haemorrhages on the heart and excess pericardial fluid (not unlike an enterotoxaemia PM.). I suspected plant poisoning and walked back down the road looking for weeds that the sheep may have eaten. Wild sage plants gave off the same strong smell that you could detect in the rumen contents. Samples of rumen contents and plant material tested positive for nitrate.


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