Local disease watch - October 2015
Disease surveillance undertaken by district veterinarians helps to support Australia's claims of freedom from a number of exotic animal diseases. These on-farm investigations of flock and herd problems also help to improve the welfare and productivity of livestock. Among the issues investigated this month are worms and scouring in sheep and cattle, deaths of newborn calves, abortions in cattle, flystrike in lambs after marking, scabby mouth, and congenital defects in calves.
Worms in sheep
There has been an explosion of worms in many sheep flocks across the region over the past six weeks causing weight loss, scouring and deaths. All ages and classes of sheep have been affected, including lambing ewes, hoggets, rams and wethers. In many cases, sheep were grazing short, heavily frosted or waterlogged native pastures. Black scour and brown stomach worms have been the main offenders. These worms reduce appetite and alter digestion, with some managers observing that sheep should look better on the feed in front of them. Heavy worm burdens were picked up quickly, often reaching fatal levels before worm egg counts had time to rise, and only four to six weeks after drenching. Interestingly, some affected sheep had "bottle jaw", a soft fluid swelling under the lower jaw. This feature is more commonly associated with the anaemia caused by barber's pole worms or liver fluke, however with heavy burdens of scour worms it is due to protein loss.
Other flocks still show high counts of barber's pole worms. While these sheep may look ok, it is now warm enough for worm eggs in their faeces to hatch. Left unchecked, warm moist conditions during spring allow the population of barber's pole worm larvae on pasture to increase rapidly. Sheep may quickly become anaemic and die. Submit faeces for a worm egg count, and ask the laboratory to determine the type of worm present.
Deaths of newborn calves
It is always a concern when a cow or heifer carries her pregnancy for nine months only to lose the calf at birth. Every year, district veterinarians investigate a number of mortalities in newborn calves. Often, the cause of death cannot be determined, even after expensive laboratory tests. Many of the cases this year appear to relate to slow delivery of the calf, with autopsies showing the calves died during or shortly after birth. Over-fat cows and heifers grazing pastures with low nutritional value in late pregnancy may have weaker contractions. At the same time, the birth passage through the pelvis becomes obstructed by excessive body fat. A number of publications available from both DPI and MLA websites deal with maintaining cows and heifers in optimal condition for calving.
Calves in three herds have been observed with unusual genetic defects this year. Occasional newborn animals with congenital defects at birth are seen in all species, including humans. However, the cases reported this year fit the description of "curly calf" of Angus cattle. This condition goes by the scientific name of Arthrogryposis Multiplex, or "AM". It has only affected a few calves in each herd, in keeping with the fact that mating a carrier cow to a carrier bull will result in only a 25% chance of the calf being affected. The Angus Society is aware of a number of genetic conditions in cattle imported into Australia that were used widely in developing the breed here. In addition to AM, another genetic condition causes calves to develop extra organs and limbs (developmental duplication or "DD"), while another causes the brain to be replaced by water (NH). A fourth condition causes curvature and weakness of the hindlimbs. The Angus Society and its member studs have been active in identifying carrier animals within studs. By eliminating the use of carrier bulls, no further cases of these "recessive" conditions will occur in commercial herds. Look for details of these tests in Angus bull sale catalogues.
Scabby mouth in sheep and goats
Scabby mouth is a viral disease that causes thick scabs to form on the lips and occasionally feet of sheep and goats. People handling affected animals may also develop infection, most commonly at the site of a recent abrasion on exposed skin. The virus is very widespread, and survives for many years in the environment when scabs fall off infected animals. It can be introduced to uninfected herds through the movement of sheep carrying infectious material, or via the use of equipment that has been contaminated with the virus. Many flocks see outbreaks in young animals every year as successive batches of lambs or kids become exposed to the virus for the first time. Despite the seemingly disfiguring appearance of the lesions and the eating or walking difficulty it causes, few animals die as a result of scabby mouth. The infection runs its course over about a month, with recovered animals having good immunity. This year, a couple of reports of scabby mouth in hand-reared poddy lambs remind us of the importance of simple hygiene practices, such as hand washing and covering any skin cuts and abrasions, when handling livestock.
Abortions in cattle
Vibriosis is a sexually transmitted disease of cattle, and a common cause of infertility. Bulls are the carriers of this bacterial disease, but show no symptoms. When "vibrio" is first introduced into a herd, many cows and heifers are slow to go into calf, often seen as an increase in the number of late pregnancies and "empties" at pregnancy testing. At subsequent joinings, older females have some immunity to infection, but not the heifers. A variation to this usual pattern of infection has been seen recently. Vibriosis has been diagnosed as the cause of several abortions in herds where cows were pregnancy tested in calf, but failed to calve. Vibriosis is prevented easily by vaccination, with vaccination of bulls alone effective in most herds. There is a great risk of introducing the infection into herds that share a bull, with vibrio vaccination providing relatively cheap insurance.