Passage of legume and grass seeds through the digestive tract of cattle and their survival in faeces.
Abstract
The potential of dissemination by livestock as a method of spreading pasture species into inaccessible areas was studied. Seeds of 10 legumes and 8 grasses found in tropical and subtropical pastures were placed directly into the rumens of cattle. Their survival and rate of passage through the digestive tract was studied over a 160-h period. After excretion, the survival of seed was followed in dung pats. Overall, more legume seeds than grass seeds survived passage through the digestive tract but there was marked variation between species in both grasses (0-64%) and legumes (0-78%). Survival of the legume seeds, both in the animal and in the dung, was largely dependent on the fraction of hard or impermeable seed in the sample. Soft seed swelled on imbibition, the seed-coat ruptured, and seeds became fragmented especially after 70 h in the digestive tract. No common mechanism appeared responsible for the survival of grass seeds in the tract. However, seeds of Pennisetum clandestinum, which are consumed heavily by cattle, survived better than seeds of tall tussock grasses which are rarely eaten. There was a 2-fold difference between legume species in the time of 50% of seed to be excreted. Over 83% of this variability was accounted for by specific gravity, proportion of hard seeds and seed size; large dense seeds with little hard seed had the fastest rate of passage. It was concluded that there was considerable potential for the dissemination of hard-seeded legumes such as Stylosanthes spp. by cattle, but not for dissemination of tall tussock grasses.