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South Australia worms, flies and lice update - June 2020

SA WormBoss Worm Control Programs

SA WormBoss Drench Decision Guides





Adelaide: Colin Trengove, Sheep Health Lecturer (UA Roseworthy campus) (trengovet@icloud.com)

Winter has arrived…. wind and rain in abundance and single-digit minimum temperatures. The implications for worms are good for survival despite inundation in some soils. While frosts, in theory, can kill exposed larvae of Haemonchus contortus (barber’s pole worm) on pasture, our New England NSW friends know that they survive unscathed through many frosts, and sometimes even snow, to contaminate the spring-lambing paddocks. Flies also cannot cope with these cold conditions, but lice delight in the warm moist microclimate on the skin away from sunlight.

Recent monitoring indicates generally low to modest worm burdens in ewes and autumn drop lambs. Feed on offer at this time is better than in recent years following the good break in late April, but pasture growth has now slowed to a dawdle with the onset of winter. Ewes mostly appear to be in good condition, but there have still been recent reports of pregnancy toxaemia (‘twin lamb disease’) following confinement feeding on hay-only which is an energy deficient diet for a late pregnant ewe. These situations of death by starvation always leave me bereft for the welfare of the ewes and unborn lambs given these losses are so unnecessary as well as extremely costly.

I expect the recent low to moderate worm egg counts at least partially reflect the conservative approach of routinely drenching ewes pre-lambing. In addition, drench capsules given to ewes pre-lambing seems to be common practice in some areas with the intent of promoting a few months of “worm free” grazing. While this approach is generally contrary to best practice because it potentially encourages drench resistance, the risks are relatively low when green feed is abundant because there is a large population of larvae on the pasture that are not exposed to the chemical released from the capsule. However, it is a topic that needs more research as there is little work published on the consequences and efficacy of capsule use pre-lambing.

Husbandry procedures such as yarding, drenching, vaccinating, crutching, shearing and droving should be avoided in the last 2–3 weeks before lambing as these stresses can predispose to hypocalcaemia (‘milk fever’), dystocia (difficult birth) and lamb loss. These risks are made worse by nutritional deficiencies or scouring due to worm burdens and other infections as they further reduce the absorption of critical nutrients in the lead up to lambing. Other risk factors include prolonged grain feeding or grazing green feed on acidic soils without providing a calcium supplement. The diet during this period should include an ad lib supplement of 50:50 stock lime and salt or the inclusion of Causmag or dolomite as well where grass tetany is also a risk. If you have experienced ewes appearing weak or becoming recumbent and subsequently dying under the conditions described, a lack of calcium or straight energy deficiency could be the reason. It is well worth seeking an urgent diagnosis from your animal health advisor to ensure early treatment and prevention.

A drench is rarely indicated at lamb marking, but is always recommended at weaning. It is also a good time to do a drench trial to determine the most effective drenches in your flock. If you are not able to do a drench trial, you can at least monitor the effectiveness of the drench you use by egg counting the lambs before drenching and again 10 days after drenching to compare the results. Weaning paddocks should have been chosen several months ago to minimise the worm contamination and ensure that weaners can grow at an optimal rate. Feed quality should not be a concern at this time of year, but the amount should be—ensure ewes with lambs at foot ideally have at least a 4 cm high dense green pasture (= 1200 kg DM/Ha).