DIETARY-PROTEIN FOR YOUNG GRAZING SHEEP - INTERACTIONS WITH GASTROINTESTINAL PARASITISM

Effects of protein supplementation and of nematode control on producti on responses in young grazing sheep and on nematode population dynamic s were assessed. Young Merino wether sheep (n = 270) were allocated to one of three supplementation (Su) treatments and one of three regimes of nematode control (drench, Dr) in a factorial design. Each of the n ine treatments was replicated three times in a randomised complete blo ck. Animals received no supplement (SuO) or were given supplements at a level equivalent to 200 g day(-1), fed three times a week. The suppl ements contained 25% lucerne meal with either 75% sunflower meal (Su1) or 75% formaldehyde-treated sunflower meal (Su2). Nematode control re gimes were: not drenched unless survival of individual animals was thr eatened (Dr0); drenched according to a strategic drenching programme ( Dr1); treatment with a controlled-release albendazole capsule (Dr2). I nfections with Haemonchus contortus were suppressed by use of closante l. Due to drought conditions and lack of pasture growth, lucerne hay w as fed to all sheep from Week 14 onwards (350 g per head per day, fed twice a week). Supplementation reduced the need for 'survival drenchin g' in Dr0 sheep considerably. Live-weight gain was increased significa ntly by supplementation with Su1 or Su2 during the 36-week experiment. Undrenched animals given Su1 or Su2 tended to grow faster than unsupp lemented animals in the Dr1 and Dr2 groups. Greasy wool production and fibre diameter were increased by supplementation and anthelmintic tre atment. Faecal worm egg counts (FEC) in undrenched sheep were signific antly lower for Su1 and Su2 sheep than for SuO sheep. There were no ef fects of supplementation on FEC in Dr1 or Dr2 sheep. Worm burden was g enerally unaffected by supplementation, while the drenching treatments Dr1 and Dr2 reduced worm burden at Week 16 and to a lesser extent at Week 27. Trichostrongylus colubriformis was the predominant nematode s pecies, with smaller numbers of Nematodirus spp., Trichostrongylus vit rinus, Trichostrongylus axei and Ostertagia circumcincta also present. It was concluded that supplementary feeding with protein meal substan tially reduced production losses attributable to nematode infections i n young grazing sheep. This appears to be due to an enhanced resilienc e of the host, rather than any major changes in development of protect ive immunity.