Abstract
Senesced annual legumes provide nutrients for small ruminants during summer, yet grazing pressure may significantly deplete seedbanks. We quantified seed passage and nutritional value of pods from 15 modern pasture legume cultivars fed to sheep in metabolism crates. Seed passage ranged from 8% (serradella, Ornithopus spp.) to 87% (biserrula, Biserrula pelecinus), with significant differences observed between species and among accessions within species. To extend the analysis, we incorporated 38 data points from historical studies, revealing that seed passage was best predicted by an exponential regression model incorporating individual seed mass and hardseededness. Seed passage declined sharply with increasing seed mass; a 0.3 mg increase corresponded to a 25% reduction in passage. In clovers (Trifolium spp.), hardseededness and seed mass were strong predictors of seed passage, explaining 64% and 58% of the variation. In contrast, seed mass accounted for 27% of variation in passage of medics (Medicago spp.). Dry matter digestibility of pods (51%–63%) and seeds (75%–90%) varied, as did crude protein content. If a sheep consumed 1 kg of pods, the ME apparently digested from 0.3 to 6.9 MJ, while energy lost via seed passage was 0.3 to 2.7 MJ. Bladder clover (Trifolium spumosum) appears well-adapted to endozoochory, producing large quantities of small, hard seeds (42% passage) that are embedded in senesced pod material that is nutritionally rich and easily prehended. Agronomists can improve persistence and summer feeding value of aerial seeded legumes by selecting for traits associated with feeding value and seed passage.
