Sheep Diseases in Feedlots

There are numerous health and disease issues commonly found within feedlot systems. Many are easily preventable, through vaccination (clostridial diseases, arthritis, scabby mouth) or grazing management (mineral and vitamin deficiencies) prior to entering the feedlot. Management within the feedlot is also an important means of preventing the outbreak and spread of ailments such as pinkeye, pneumonia/pleurisy, prolapse, salmonellosis and coccidiosis. Urea poisoning and the negative effects of toxins (mould and fungal) are specific feed-related issues that can be prevented through careful ration preparation and testing.

Following are three of the more common health and/or disease issues found within feedlot systems. Veterinary staff and/or extension officers can assist with the diagnosis and management of all health- and/or disease-related issues.

Acidosis (Grain Poisoning)

Lambs that are not accustomed to grain are prone to acidosis. Lambs eating relatively small amounts of grain, or pelleted ration with a high starch content can develop acidosis due to the production of high concentrations of lactic acid within the rumen. Lactic acid accumulation can cause distress, diarrhoea and/or death.

Grain poisoning is most likely to occur when:

• Lambs are being introduced to grain
• There is a sudden increase in grain intake (e.g. following wet weather)
• There is a change of grain source in the ration.

The gradual introduction of the grain content in the ration is essential if grain poisoning is to be avoided. Loose droppings are an early indication of digestive disorders. If this occurs, maintain the ration at the existing grain level until droppings firm. Sometimes it will be necessary to drop back to the previous level of grain feeding. If the droppings develop a watery consistency, return to hay-only feeding and recommence grain introduction when droppings have returned to normal.

Symptoms of acidosis in lambs may include scouring, abdominal pain, a sluggish and dehydrated or bloated appearance, and a characteristic arching of the back.

Treating lambs suffering from acidosis is difficult and rarely successful unless lambs are identified and treated within the early stages of developing the disorder. Lambs should be removed from feedlot pens and drenched with 60 g of Causmag (magnesium oxide) or 15 g of sodium bicarbonate in 1 L of water, in an effort to neutralise acids produced within the rumen. Alternatively, drenching with 10–20 mL of paraffin or light vegetable oil and/or dishwashing liquid will enable lambs to belch the gas and foam that has formed within the rumen during the early stages of acidosis. Gas and foam can cause distension of the rumen, which restricts lung movement and frequently leads to death by asphyxiation. Affected sheep should be given hay until they recover.

Numerous additives may be used in rations to reduce the likelihood of acidosis. Most do not prevent lactic acid production but may help to reduce its effects on the lamb. The following are the most commonly used additives.

Sodium bentonite is a clay that swells when in contact with rumen fluids, slowing down the passage of food in the gut. It binds acid ions to its surface and reduces the risk of excessive starch fermentation. It may reduce ration intake and lower feed digestibility. Add at a rate of 1%–2% (w/w).

Sodium bicarbonate is an alkali and acts as a ‘buffer’ against moderate increases in acidity following the intake of starch-rich grains. It is safe to feed throughout the feedlot process. Once lambs are accustomed to a ration it may be removed; however, you should be wary of periods when lambs may ‘go off’ feed. Reintroduce sodium bicarbonate within the grain ration or in loose lick troughs within the feedlot if this occurs. Add at a rate of 1%–2% (w/w). May be removed within two weeks of lambs starting the finishing ration.

Ground limestone will help correct calcium deficiencies and buffer against acid production within the rumen and small intestine. Add at a rate of 1%–1.5% (w/w).

Acid Buf is a seaweed extract high in calcium and magnesium carbonate. It is a buffer with a high surface area structure capable of binding acid ions. It is slow-acting and provides prolonged buffering within the rumen. Add at a rate of 1%–2% (w/w).

Bovatec is an ionophore that modifies rumen fermentation and changes volatile fatty acid patterns within the rumen. Registered to prevent coccidiosis, Bovatec may also reduce acidosis risk and improve feed conversion efficiencies but may also reduce intake. Add 30–75 g per tonne of feed.

Virginiamycin is an S4 antibiotic that prevents the growth of lactic acid-producing bacteria within the rumen. It requires veterinary approval for use. Discuss the use of antibiotics, such as Virginiamycin, with your processor, as several export markets do not allow antibiotic use.

Laminitis

Laminitis is similar to ‘founder’, an ailment commonly found in horses. Affected animals appear lame and are hesitant to stand or move unless provoked. A form of acidosis, laminitis is caused by the release of toxins within the bloodstream following consumption of excess dietary energy or protein. Affected animals may recover within several days. Provision of reasonable-quality roughage and/or removal of affected animals from the feedlot will facilitate recovery.

Bladder Stones

Also known as water belly and urinary calculi, bladder stones commonly develop when rations are low in calcium relative to phosphorus. High magnesium intakes, low roughage, poor water quality and low water intake may also lead to the formation of ‘stones’ within the bladder and/or kidney tracts. If blockage of urine flow occurs, the lamb’s bladder will eventually burst, leading to the swollen ‘water belly’ appearance, and the death of the affected animal.

Prevent the formation of stones by adding limestone to increase calcium intake on high-grain diets. You need to ensure that the calcium to phosphorus ratio within the ration is greater than 1.5:1. Ensure that rations contain adequate fibre and that good-quality water is available, to stimulate intake. Adding salt to rations will help increase water intake. Alternatively, the addition of anionic (acid) salts at 0.5% (w/w) may improve calcium mobilisation within the small intestine and acidify urine to help dissolve forming stones.

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