TY - JOUR

T1 - Merino ewes bred for parasite resistance reduce larval contamination onto pasture during the peri-parturient period

AU - Williams, Andrew Richard

AU - Greeff, J C

AU - Vercoe, P E

AU - Dobson, R J

AU - Karlsson, L J E

PY - 2010

Y1 - 2010

N2 - The peri-parturient period is crucial for controlling worms as the acquired immunity of ewes is disrupted, resulting in an increase in faecal worm egg counts. Two hypotheses were tested in this experiment - that ewes bred for worm resistance would have lower faecal worm egg counts than unselected control ewes, during late pregnancy and lactation, under similar but separate grazing areas; and also that numbers of infective nematode larvae would be lower on pastures grazed by resistant ewes than pastures grazed by unselected control ewes. Faecal samples were collected from resistant and unselected ewes in late pregnancy and early lactation, during the winter rainfall season, and analysed for numbers of Trichostrongylus colubriformis and Teladorsagia circumcincta. Pasture samples were taken 1 week before and 7 weeks after lambing started and analysed for infective larvae. In all sheep, worm egg counts rose 2 weeks prior to lambing and continued into lactation. Worm egg counts were significantly lower in the resistant ewes from 1 week before lambing to 2 weeks after lambing. There were no differences in egg counts between single- and twin-bearing ewes in the resistant line. However, twin-bearing control ewes had significantly higher egg counts than single-bearing control ewes. Following lactation, plots grazed by resistant ewes had substantially less contamination with T. colubriformis larvae, but there were no differences in numbers of T. circumcincta larvae. Our results demonstrate that sheep bred for worm resistance has lower worm burdens during the peri-parturient phase and that lambs born to resistant ewes face a lower larval challenge during their introduction to grazing. In our environment, selection for low worm egg counts has produced sheep highly resistant to T. colubriformis, but has had less impact on resistance towards T. circumcincta.

AB - The peri-parturient period is crucial for controlling worms as the acquired immunity of ewes is disrupted, resulting in an increase in faecal worm egg counts. Two hypotheses were tested in this experiment - that ewes bred for worm resistance would have lower faecal worm egg counts than unselected control ewes, during late pregnancy and lactation, under similar but separate grazing areas; and also that numbers of infective nematode larvae would be lower on pastures grazed by resistant ewes than pastures grazed by unselected control ewes. Faecal samples were collected from resistant and unselected ewes in late pregnancy and early lactation, during the winter rainfall season, and analysed for numbers of Trichostrongylus colubriformis and Teladorsagia circumcincta. Pasture samples were taken 1 week before and 7 weeks after lambing started and analysed for infective larvae. In all sheep, worm egg counts rose 2 weeks prior to lambing and continued into lactation. Worm egg counts were significantly lower in the resistant ewes from 1 week before lambing to 2 weeks after lambing. There were no differences in egg counts between single- and twin-bearing ewes in the resistant line. However, twin-bearing control ewes had significantly higher egg counts than single-bearing control ewes. Following lactation, plots grazed by resistant ewes had substantially less contamination with T. colubriformis larvae, but there were no differences in numbers of T. circumcincta larvae. Our results demonstrate that sheep bred for worm resistance has lower worm burdens during the peri-parturient phase and that lambs born to resistant ewes face a lower larval challenge during their introduction to grazing. In our environment, selection for low worm egg counts has produced sheep highly resistant to T. colubriformis, but has had less impact on resistance towards T. circumcincta.

U2 - 10.1017/S1751731109990802

DO - 10.1017/S1751731109990802

M3 - Journal article

C2 - 22443626

VL - 4

SP - 122

EP - 127

JO - Animal

JF - Animal

SN - 1751-7311

IS - 1

ER -