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Beyond the Bale : March 2018
WHAT IS THE PROBLEM? Ewes start to lose immunity to worms during late pregnancy with the effect starting earlier and being more severe with poorer feed quantity and quality. The establishment rate of worms, that is, the percentage of infective worm larvae consumed with pasture that establish to become adult worms in the sheep, increases at these times. To put this into perspective, only 5–10% of worm larvae will establish in a dry ewe in good condition and on good feed. During early lactation, that may rise to a level where 40–60% of the infective larvae are able to establish to adult worms. Before worm egg counts (WEC) start to rise, 56 For most properties, a breeding ewe flock rather than wethers drives profit, but they also drive worm contamination of pastures. This results in an ongoing source of infection, not just for the ewes, but also for their lambs and other sheep on the property. However, a number of strategies can be used to combat this issue. changes occur in the immune response of the pregnant ewe that signal the ewe is losing immunity. These changes can occur as early as three weeks prior to lambing and lead to an increase in worm egg count and worm burden. The rise in WEC is worse in ewes with multiple lambs and on low nutrition, and they will also take longer to recover after weaning. Figure 1 right shows a comparison of worm burdens of ewes on either a low or a high- quality diet and in different reproductive stages. It shows that the dry ewes had a very low burden of worms – no bars are evident as the result was close to zero for both the low- and high-quality diet. However, during pregnancy and lactation the average counts rose considerably more in ewes on a low- quality diet. However, the counts of ewes that EWES: HOW THEY CAN SABOTAGE YOUR WORM CONTROL had lambs weaned early dropped noticeably, and more so in the ewes on a high-quality diet. Ewes with a higher body condition score and receiving good quality pasture through lambing maintain better immunity against worms. 56 ON FARM WORMCOUNT 12000 14000 10000 8000 6000 4000 2000 0 day 13 day 41 low high dry low high pregnant/lactating low high early weaned Figure 1. The worm burden (black scour worms) of dry, pregnant/lactating and early-weaned Merino single bearing and rearing ewes on either a low or high-quality diet. Source: Lewis Kahn.
In the Shops - March 2018