Effects of feeding willow (Salix spp.) upon death of established parasites and parasite fecundity

Two indoor feeding experiments with young sheep were conducted to compare effects of feeding condensed tannin (CT) containing willow (Salix spp.) or chaffed lucerne hay (Medicago sativa) upon death of established parasites and parasite fecundity. In Experiment 1, 24 parasite-free weaned male lambs were individually penned, fed chaffed lucerne hay ad libitum for 5 weeks and then fed either lucerne (n = 12) or willow (n = 12) diets for a further 5 weeks. Twelve days prior to willow feeding, all lambs were infected with a mixed population of 22,300 gastrointestinal nematodes comprising predominantly Teladorsagia spp. (0.93), with the remainder being Trichostrongylus, Cooperia and Haemonchus species. Voluntary feed intake, apparent digestibility, blood composition, faecal nematode egg counts, production of eggs and hatched larvae, female worm fecundity and worm burden at slaughter were measured. In Experiment 2, Teladorsagia eggs were added to the faeces of parasite-free sheep fed either lucerne or willow (n = 9) to measure proportional recovery. Recovery of added Teladorsagia eggs was 0.85 in lucerne-fed lambs and 0.53 willow-fed lambs (P<0.001) which were then used as correction factors for Experiment 1 data. Hatched larvae per g of wet faeces tended (P=0.081) to be lower for sheep fed willow than lucerne chaff (0.71 versus 0.83 of eggs added). In Experiment 1, total CT concentration in willow was 27 g/kg DM, with only traces in lucerne, while organic matter digestibility was 0.648 versus 0.599 (P<0.001) for willow and chaffed lucerne. Introduction of willow at week 6 reduced VFI (P<0.001) but this progressively increased until it was similar to lucerne-fed sheep during weeks 9 and 10. Feeding willow reduced Haemonchus contortus (P<0.01) and female Teladorsagia circumcinta (P<0.05) worm burdens in the abomasum and reduced Cooperia curticei in the small intestine (P<0.01). Adjusted total daily egg production was lower in willow-fed sheep than lucerne-fed sheep due to reductions for Haemonchus and Teladorsagia spp. (P<0.05). Per capita fecundity (i.e., eggs produced/worm/day) for H. contortus (P<0.05) and the number of eggs in utero as a measure of fecundity in both T. circumcincta and Trichostrongylus spp. (P<0.001) were lower for willow-fed sheep. Faeces incubation revealed reduced production of L3 larvae for both H. contortus and T. circumcincta (P<0.05) in willow-fed sheep. Total white blood cells, total lymphocytes and subsets of lymphocytes were similar for both diets.Feeding willow to parasitised young sheep reduced nematode worm burdens and female worm fecundity, with abomasal dwelling species being most affected and conventional methods of measuring FEC underestimated nematode eggs in the faeces of willow-fed sheep.