Effects of a concurrent infection of Trichostrongylus colubriformis on the productivity and physiological and metabolic responses of lambs infected with Ostertagia circumcincta

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Abstract
Weaner lambs were infected for 16 weeks with 900 or 3000 Trichostrongylus colubriformis larvaelweek alone, with 38 000 Ostertagia circumcincta larvaelweek alone, or with the two parasites concurrently at these dose levels. Concurrent infections with T. colubrifovmis, which when given alone had no significant effect, reduced liveweight gain by 15 kg over the 16-week infection period compared with a 6-kg reduction in liveweight of lambs infected with O. civcumcincta alone. T. colubvifovmis when given alone did not affect wool growth, but with concurrent infections wool growth was reduced by up to 66% compared with a 25 % reduction in lambs infected with O. circunzcincta alone. This greater loss of productivity in concurrent infections was principally due to reduced food consumption, and was exacerbated by a substantial decrease in the efficiency of retention of apparently digested nitrogen. These effects were accompanied by an elevated gastroenteric plasma loss, and a concomitant decrease in albumin synthesis which together were considered responsible for the more pronounced hypoalbuminaemia observed in lambs with concurrent infections. Reasons for impaired nitrogen utilization in concurrently infected lambs are discussed.