Effects of legume forages on ovine gastrointestinal parasite development, migration and survival

Lambs grazing certain legumes have reduced parasite intensities compared to lambs grazing ryegrass swards. Eighteen replicates of white clover (cv. AberHerald), lucerne (cv. Luzelle), red clover (cv. Merviot) and perennial ryegrass (cv. Abersilo) were sown at equivalent field rates in 25 cm diameter PVC pots and maintained outside for 6 months. On day 0, forage in each pot was cut to 50 mm from soil level and the pots were placed in a glasshouse (at 19–25 °C and 70% humidity) in a randomised block design. Ten grams sheep faeces containing 2133 Haemonchus contortus eggs per gram were placed on the soil in each pot. Six replicates of each forage were destructively sampled on days 14, 21 and 29. Forage samples were cut at 50 mm from the soil surface and at the soil surface to give two samples per pot. The number of nematodes was determined by a modification of the Whitehead tray method. The ratio of free-living to infective-stage larvae was determined from at least 10% of the larvae. The number of H. contortus larvae kg dry matter−1 (DM) forage was calculated and the data rank transformed prior to analysis by ANOVA. There were fewer larvae on legumes compared with ryegrass on samples from forage above 50 mm (P < 0.001) but there was no forage effect on larvae below this height. The sum of larvae present on all forage per kilogram DM showed fewer larvae on red clover compared with ryegrass on day 21 (P < 0.05). There was an effect of day on the total number of larvae on forage (P < 0.001) but there were no forage × day interactions. Analysis of the data according to the leaf area above 50 mm from the soil surface confirmed these results, that there were fewer larvae on legume forages than ryegrass above this height (P < 0.01). Overall, red clover affected the development of H. contortus and all legumes affected larval migration above 50 mm compared with ryegrass but survival of larvae was similar on all forages. Further work is needed to determine if these effects of legume forages would reduce the number of parasitic larvae ingested by livestock under field conditions.