Meta-analysis of the effects of dietary inclusion of sericea lespedeza (Lespedeza cuneata) forage on performance, digestibility, and rumen fermentation of small ruminants

Abstract

For more than 20 years, the nutraceutical forage sericea lespedeza ‘AU-grazer’ (SL; Lespedeza cuneata) has been used as an alternative to anthelmintic drugs for controlling gastrointestinal parasites in small ruminants, but with little attention to animal performance. Thus, the objective of this study was to evaluate the effects of dietary inclusion of SL on performance, digestibility, and rumen fermentation of small ruminants using a meta-analytic approach. A total of 24 peer-reviewed manuscripts (sheep = 6 and goats = 18) from 2000 to 2020 met the inclusion criteria for the analysis. Raw mean differences between dietary SL and control treatments weighted by inversed variance were compared with a robust variance estimation. Diet characteristics like crude protein content, NDF content, condensed tannin (CT) content, and inclusion level of SL in the diet (0% to 100%) were used as covariates in a metaregression and subgrouping analysis. Compared to the control, dietary inclusion of SL decreased (P < 0.05) total-tract digestibility by 12% (DMD) and average daily gain (ADG) by 17.7%, but no effects were observed in dry matter intake. Likewise, dietary SL reduced (P < 0.05) molar proportion of acetate (68.88 vs 71.8%), but increased butyrate (10.3 vs 9.2%) and propionate (17.9 vs 16.8%) molar proportions in the rumen. Consequently, dietary SL reduced CH4 emissions by 38% compared to the control. Despite the high heterogeneity in the response variables (I2 > 50), no significant bias was detected (funnel test; P > 0.05). The dose-response analysis revealed that SL-based diets should not include more than 60% in the diet to prevent negative effects in DMD and ADG. Likewise, low inclusion level of SL in the diet (from 30 to 40%) linearly increased propionate concentrations in the rumen but reduced CH4 emissions. In addition to the nutraceutical benefits of this forage, SL inclusion improved rumen fermentation (increased propionate, reduced CH4) at low rates of inclusion, but reduced ADG in small ruminants at higher rates, with these effects minimized if dietary inclusion rate for SL is 60% or less. Further research is needed to determine the optimum inclusion rate to balance nutritional and pharmaceutical effects of SL in the diet of small ruminants.