Temporal effects of protein nutrition on the growth and immunity of lambs infected with Trichostrongylus colubriformis

The aim of this research was to determine whether metabolisable protein sup ply during the early period of infection with Trichostrongylus colubriformi s influenced resilience and the later stages in the development and magnitu de of host resistance in previously nematode-naive lambs. Eighty TexelxGrey face lambs were fed pelleted feeds calculated to provide grossly different amounts of metabolisable protein. Sixty of the lambs received a trickle inf ection of T, colubriformis and 20 lambs were kept as uninfected controls. T here were four initial groups. namely infected or uninfected and fed either a moderate or a high protein feed. After 5 weeks of infection, a further f our groups were established by changing the feed of half of the animals fed the moderate protein feed to the high protein feed and of half of the anim als fed high protein to the moderate protein feed. Live weight gain and fee d conversion ratio were greatest for lambs fed the high protein feed and we re reduced by infection. Faecal egg counts, worm burdens and per capita fec undity of adult female nematodes were unaffected by changes to metabolisabl e protein supply. Decreasing metabolisable protein supply following 5 weeks of infection reduced live weight gain without any effect on resistance to T. colubriformis. Haematological variables, indicative of improved resistan ce, were also largely unaffected by metabolisable protein supply. It is con cluded that the requirements of immune function probably had priority over those of growth and that the metabolisable protein supply provided by the m oderate protein feed was sufficient to account for the requirements for the expression of immunity. It Is probable that the potential for metabolisabl e protein supply to enhance resistance to infection from T. colubriformis i s dependent on the levels and magnitude (i.e. in relation to maintenance re quirements) of metabolisable protein supply being compared and the demand o f other competing physiological functions. (C) 2000 Australian Society for Parasitology Inc. Published by Elsevier Science. All rights reserved.