Effect of the condensed tannin containing hay, sericea lespedeza, on natural and experimental challenge Haemonchus contortus infection in lambs
Parasitic infection is one of the leading economic scourges for sheep and goat production. This problem is exacerbated as the resistance of nematode populations to chemical treatment (anthelmintics) becomes increasingly common. Condensed tannin (CT) containing plants used as forage and CT extracts mixed in processed feeds have become a growing focus of research aimed at finding novel solutions to the problem of nematode infection and chemotherapy resistance. This study was conducted to evaluate the effect of the CT containing forage, sericea lespedeza (SL), fed as hay, on Haemonchus contortus infection in Gulf Coast Native sheep. Twenty-eight naturally infected lambs were removed from pasture and maintained in cement floored pens. Lambs were divided into four groups (seven animals each): Group 1) control, natural infection and fed bermudagrass hay; Group 2) dewormed and fed bermudagrass hay; Group 3) natural infection and fed SL hay; Group 4) dewormed and fed SL hay. All animals received trickle infections of 1000 L3 (infective stage) H. contortus larvae three times a week for three weeks. SL hay feeding was stopped after seven weeks and three animals from each group were necropsied at nine weeks to determine effects on worm numbers. SL effects on ovine health (resilience to infection) and egg output (worm fecundity) were determined by weekly measurements of packed cell volume (PCV) and fecal egg count (FEC) for each sheep. Reduction in FEC for both groups 3 and 4 remained >75% through week seven. After SL hay feeding stopped, FEC reduction dropped substantially to 35-50%. Necropsy results indicate that SL had a lethal effect on established worm populations but little or no effect on the survival of incoming larvae.