The effect of strategic anthelmintic treatment on the breeding performance of hill ewes

A series of field trials involving 3500 Scottish hill ewes was carried out to determine the effect of different worming routines on subsequent flock performance. Combinations of the following seasonal dosings were examined in April lambing flocks: “early winter” (November/early December); “winter” (mid-January to early February) and “spring” (mid-March to early April). The effects upon numbers of barren ewes and on rearing percentages in comparison with untreated control sheep were evaluated.Barrenness was significantly reduced by the following treatments: “early winter” by 70% (P<0.10); “winter” by 7.8% (P<0.05); “early winter and winter” by 4.3% (P<0.05). Rearing percentages were significantly increased by the following treatments: “early winter and winter” by 10.7% (P<0.01); “early winter and spring” by 9.2% (P<0.01); “spring” by 7.9% (P<0.05).The increased rearing percentages indicated that a strategic dosing programme for breeding ewes between mating and parturition is worthwhile, with the routines involving two doses — either ”early winter and winter” and “early winter and spring” giving the greatest benefit.Attention is drawn to the high incidence of barrenness and low rearing percentages which was a constant feature in all the flocks used in the trial.