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Direct effects of condensed tannins on gastrointestinal nematodes in grazing Angora goats

B. R. Min, D. Miller, S. P. Hart, G. Tomita, E. Loetz, and T. Sahlu

E (Kika) de la Garza American Institute for Goat Research, Langston University, Langston, OK

The objective of this study was to evaluate effects of condensed tannin-containing, Serica lespedeza (SL; 5.2% condensed tannins (CT)), on fecal egg count (FEC; eggs/g), rate of larva development (RLD), adult worm burden (AWB), and immune response (IMR) compared with a control forage (CF; crabgrass/tall fescue; 0.2% CT) in grazing Angora does and kids. Fifty worm-free does were randomly allocated to three treatments. One treatment (10 does; 45 ± 1.5 kg) was grazed on SL forage from April 25 to July 15, 2002 (81 d), and a second treatment (20 does; 43 ± 1.4 kg) grazed CF. A third treatment (20 does; 44 ± 1.4 kg) was introduced to a sward of SL for 2 wk and then was switched to CF for 2 wk (MIX), fellowed by repeated change every 2 wk. The FEC was determined every 2 wk. RLD was evaluated on d 60. To gauge levels of infective larvae on pasture, three worm-free kids (12 ± 0.98 kg) were randomly selected and introduced into each treatment as tracers. Tracers grazed for 60 d and were euthanized for determination of AWB. The IMR of does was measured by skin thickness reaction after injection of 250 g phytohemagglutinin (PHA). Mean FEC for SL and MIX were substantially lower (P < 0.01) than for CF in does (186, 428, and 1148, respectively) and kids (550, 2,757, and 3,600, respectively). Total fecal egg output (3.3, 6.0, and 26.9 × 105/d, respectively; based on FEC and fecal output) and RLD (242, 263, and 792, respectively) were markedly lower (P < 0.05) for SL and MIX than for CF. Tracers on SL and MIX had lower (P < 0.01) AWB than CF in the abomasum (100, 333, and 783, respectively) and AWB was lowest among treatments (P = 0.06) in the small intestine for SL (117, 433, and 350, respectively). Abomasal worms were dominated by Haemonchus (52%), but Trichostrogylus were predominant (71%) in the small intestine. The IMR of does was similar among treatments at 0 h. However, IMR was greater (P < 0.01) for SL (4.9 mm) and MIX (6.0 mm) than for CF (3.0 mm) at 12 and 24 h after injection of PHA. In conclusion, these results indicate that CT in forages can reduce contamination of pastures with infective larvae. Grazing CT forages reduced FEC, RLD, and AWB, and also appeared to enhance IMR.


 

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