The effects of parasitism on ewes for prime lamb production in western Victoria

Context Internal parasites are estimated to cost the Australian sheep industry AUD436 million per annum (p.a.). Aims To assess effects of parasitism in flocks producing prime lambs 500–700 mm p.a rainfall. area Victoria. Methods Ewes on two farms that followed ‘best practice’ gastrointestinal parasite control programs (BP) and did not (regionally typical, TYP) were compared. Separate cohorts ewes monitored from pregnancy scanning their subsequent joining each year for three consecutive seasons. Observations included worm egg count (WEC), bodyweight, condition score presence breech soiling (dag). These compared between groups treated suppress (SUP) those according usual program used farm (NSUP). Data individual analysed using a multivariable, mixed-effects regression model. Key results After adjusting known confounders, SUP 1.2 (95% CI 0.80–1.6) kg heavier than NSUP ewes. Mature significantly at next 6 18 occasions, mostly following winters when experienced nutritional stress. Ewe hoggets Merino generally more susceptible mature non-Merino ewes; single-bearing less bearing twins. The reduced peri-parturient had an optimal grazed adequate pastures. Conclusions vulnerable immature, twin-bearing, or under Some greatest differences occurred periods low feed availability and/or ewe score. difference mean bodyweight Merinos was always greater non-Merinos. WECs sole reliable indicator this class sheep. Implications Immature twin-bearing ewes, suboptimal body condition, should be managed considering increased vulnerability parasitism, WEC interpreted alongside other factors. Controlled release capsules effective reducing production loss nematodes most years but may clinical some cases.