The rapid increase in the magnitude of anthelmintic resistance towards commercial chemical anthelmintics, calls for alternative methods to complement treatment or replace anthelmintics. During the last two decades more and more calls have been made for a holistic management solution. Recent studies on breeding for resistant animals and bioactive forages highlight the potential of these to contribute towards parasite control.
For this study, gastrointestinal infection in a merino flock was investigated by means of faecal egg counts (FEC). The level of parasite infection in weaned merino lambs in their first summer could be linked to weather conditions. Anthelmintic resistance in the flock was quantified and compared to the resistance level some years earlier. Within the flock, 18% of the ewes appeared to be resistant with consistently (P<0.05) lower FEC than the rest of the flock.
Lespedeza cuneata, a tannin-containing legume, is, according to scientific literature, one of the promising bioactive forages. Depending on the level of condensed tannin (CT), ruminant digestion can be complemented or compromised by the tannins. Small plot trials were conducted to establish production criteria for L. cuneata, currently lacking in South Africa. The grand mean dry mass (DM) yield for the first growing season, (characterized by above normal rainfall), was 8.3 t ha-1, compared to the 2.56 t ha-1 for the second growing season, (characterized by below normal rainfall). Highly significant differences (P<0.001) were measured between the yields produced under different cutting frequencies (6, 8 and 12 weeks) and cutting heights (5 cm and 15 cm). Except for crude protein levels, ADF (acid detergent fibre) and NDF (neutral detergent fibre) analysis of the complete plant indicated a less acceptable nutritional quality. Since sheep selected leaves during grazing, separated leaf samples were analysed. Chemical feed analyses of leaves were more favourable, compared to feed analysis of the whole plant. The condensed tannin (CT) content of leaves increased significantly (P<0.05) with increased moisture stress and varied between 24.5 and 122 g kg-1 DM over the growing seasons. Different dried herbage diets were offered to Merino ewes in a follow-up trial to evaluate the anthelmintic properties of the forage. The leaf portion of Lespedeza cuneata hay and Medicago sativa hay was offered ad libitum to confined sheep. Lespedeza cuneata is a tannin rich legume, while Medicago sativa, known for its very low tannin content, was used as control. FEC were significantly (P<0.05) lower in the Lespedeza group after 35 days.
To determine the influence of condensed tannin (CT) level on the hatch efficacy of Haemonchus contortus eggs, acetone leaf extracts of L. cuneata plants with different condensed tannin contents (73.5, 88, 102 and 122 g kg-1 DM) were tested in an in vitro assay on H. contortus eggs. Concentrations of between 0.63 and 20 mg ml-1 were used in the assay. Concentrations higher than 10 mg ml-1 led to complete inhibition of egg hatching with all the plant extracts regardless of CT content. A typical dose related response of the extracts of plants with very high tannin content was found, but not with plant extracts containing lower tannin concentrations.
The results of the study indicate that L. cuneata can be incorporated in a fodder flow programme as an alternative or complementary strategy to other methods, to manage the detrimental effect of gastrointestinal parasites in sheep.