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Local disease watch - August 2015

The range of problems seen by district veterinarians this month is typical for this time of year. Most of the issues affecting livestock are related to the winter decline in pasture quality and quantity and the district cycle of calving and lambing.

Foot abscess

Foot abscess is a painful, debilitating infection of the deeper tissues of the foot, causing severe lameness in sheep, goats and cattle. Two types of foot abscess are described in sheep: toe abscess following injury to a weak or overgrown claw; and the more common heel abscess when infection gains entry to the foot through damaged skin between the claws. The organisms involved are those found in soil and sheep yards. The added weight of a heavy pregnancy which splays the claws of older ewes, constantly wet pasture in winter which softens the skin, foot scald infection and muddy yards all increase the likelihood of foot abscess. A pregnant ewe with sore feet lies around at a time when she needs to be grazing, with fatal pregnancy toxaemia a frequent complication.

Avoid handling sheep in muddy yards, especially ewes in late pregnancy. Foot bathing with zinc sulphate to control scald helps prevent foot abscess, but is of no benefit once abscess develops. There is little point to mustering ewes just to footbath them; instead, have a footbath set up to walk sheep through as they leave the yards following other routine procedures. Early treatment of sheep affected with foot abscess is recommended, using a long-acting antibiotic injection.

Pregnancy toxaemia

Pregnancy toxaemia in sheep and the related condition of ketosis in beef cows are more frequent this year. Many producers struggled to control the weight of cows and ewes earlier this year, amidst abundant autumn feed. Those same fat cows and ewes are now losing weight late in pregnancy, with heavy frosts curtailing pasture growth and reducing pasture quality. We have seen several cases where ewes in late pregnancy carrying large twin lambs have little room left for food. They can't eat enough of the bulky, low quality frosted pasture to sustain themselves. Ewes affected with pregnancy toxaemia stand alone, apparently blind. They are weak, and soon go down and die. Treatment with oral energy supplements and an anti-inflammatory injection may save those still on their feet. It is important to recognise the symptoms of pregnancy toxaemia, and to immediately correct the energy imbalance causing the problem in the mob. A change to a better pasture or feeding an energy supplement is required urgently.

Grass Tetany

Grass Tetany has been causing deaths in cows in the district throughout this late autumn and winter. Winter grass dominant pastures or crops are notoriously low in Magnesium, Calcium and Sodium and high in Potassium and Nitrogen which limit the availability of the Magnesium to the cows. Cattle most at risk are those that calved between April and August. Cattle only have a very small store of Magnesium and must replenish their output into their milk supply daily, so they are most at risk when feeding a calf. Higher milk producers are more at risk, as are older fatter cows, and Angus and Angus crosses. Any additional stress on cattle such as weather, mustering or time off feed may trigger grass tetany. The most effective and commonly used preventative is to feed hay treated with Magnesium oxide (Causmag®). Causmag daily requirements for cattle are 60g/head/day. If daily feeding of hay is not possible some find that offering a loose lick in the paddock of equal parts causmag, lime and salt, or putting out grass tetany blocks can offer some protection.

Lice

Lice are showing up in cattle. Lice cause cattle to rub. The first sign of lice infestation is patchy hair loss between the hind legs and on the neck. There are two types of lice which affect cattle in our area, sucking lice and biting lice. Cattle lice only live on cattle, with their numbers increasing in autumn and winter. On the tablelands, cattle producers routinely wait until after the first frost before treating their cattle for lice. Few lice control products kill lice eggs, and they usually don't persist long enough to kill lice hatching from those eggs. Two treatments two to three weeks apart may be required. In addition, some products are much more effective at controlling sucking lice. So we often see a build-up of lice, mainly biting lice, in late winter causing young cattle in particular to develop a moth-eaten appearance.

The economics of treating cattle for lice has been debated for a long time. Well fed cattle appear able to control lice numbers, perhaps with the exception of bulls. Poor cattle have heavier lice burdens. Routinely treating cattle for lice is unlikely to be economical, in terms of weight gain or productivity. However, producers recognise that lousy cattle may damage hides from rubbing, and certainly damage fences and facilities when rubbing which can be costly to maintain. They also take pride in having animals that look healthy.

Alexandra Stephens
District Veterinarian
Yass
02 6118 7700
alexandra.stephens@lls.nsw.gov.au