To investigate the potential role of cysteine in the increased parasite susceptibility of sheep selected for increased wool production, ten sheep from both fleece-weight-selected (FW) and randomly-selected (C) Romney lines received either 2g of supplemental cysteine per day, or saline, via abomasal infusion. Following drenching to remove any pre-existing parasites, all sheep were dosed with Haemonchus contortus and Trichostrongylus colubriformis infective larvae. Cysteine infusion elevated plasma cysteine levels by an average of 65% (P<0.0001). Off-pasture faecal egg counts (FEC) were higher in FW than C sheep (645 versus 200 eggs/g, P<0.01). No significant effects of line or infusion treatment on FEC were observed following the trial infection, though on days 52, 57 and 58, FEC in sheep receiving saline were at least twice those of sheep receiving cysteine. Total H. contortus counts were greater in FW than C lines of sheep (1208 versus 1055, P<0.05), while total numbers of T. colubriformis did not differ between lines or infusions. This study confirms the greater susceptibility of FW sheep to internal parasites, and suggests cysteine may influence certain aspects of immunocompetency in sheep.

FM, Miller, HT Blair, GW Reynolds, and DK Revell

Proceedings of the New Zealand Society of Animal Production, Volume 58, , 150-153, 1998
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