Survival of seeds of tropical grassland species subjected to bovine digestion.
The survival and digestion of seeds of 47 tropical and subtropical legume and grass species were studied by placing the seeds in nylon bags in the rumen of fistulated cattle, followed by acid-pepsin digestion, to identify any differences likely to affect dissemination by grazing cattle. Seeds of only 4 of the 23 grass species survived in appreciable numbers; all were creeping, sward-forming species adapted to heavy grazing. Digestion for short periods increased germination of Digitaria ciliaris, Axonopus affinis and Paspalum notatum while seeds of Pennisetum clandestinum survived up to 10 d in the rumen. Few seeds of tall tussock grasses survived the digestive processes. Survival of legume seeds was closely related to the hard seed content of the sample. Soft seeds were killed within 6 h. The rate of breakdown of hard seeds during digestion varied with species. Most tropical legumes had sufficient hard seed to ensure some dissemination if ingested. Hard legume seed was little affected by up to 241 h immersion in a rumen. Digestibility of legume seed was inversely related to hard-seededness. The nylon bag technique with the 2-stage digestion gave a good prediction of which seeds could survive passage through the digestive tract of cattle. For legumes, the hard seed content gave an easy and usually reliable indication of the resistance of seed to digestion.