PARASITISM AND PRODUCTION IN FLEECE-WEIGHT-SELECTED AND CONTROL SHEEP

In two successive years young sheep (less than 6 months old; n = 80, Y ear 1; n = 117, Year 2) from a line selected for increased fleece weig ht for 37 years and an unselected line at Massey University were eithe r treated with an albendazole controlled release capsule (CRC), or wer e allowed to become subclinically infected while facing natural parasi te challenge. Subclinically infected fleece-weight-selected (FW) sheep developed higher faecal egg counts(FEC) than control (C) sheep, but t here was little evidence that FW sheep suffered greater production dep ression than C sheep. Blood gastrin levels tended to be less elevated in infected FW sheep than in C sheep suggesting that FW sheep may have suffered less gastric dysfunction than C sheep. There was no effect o f line or infection on antiparasite antibody levels. This study demons trates that long-term selection for high wool production has resulted in increased FEC, suggesting that wool production and FEC may be unfav ourably genetically correlated. Although CRC treatment was effective i n preventing establishment of an adult worm burden, the production res ponse was variable. During some periods production in CRC-treated shee p (particularly rams) was lower than in subclinically infected sheep.