Sheep are potential vectors for the spread of canola (Brassica napus) seed

Abstract

Sheep and other livestock are capable of ingesting seeds from weeds and desirable pasture species and excreting a percentage of viable seeds. As livestock are used to graze stubble paddocks after harvest, any crop seed shed before harvest or spilt during the harvesting process could also be ingested and subsequently excreted as viable seed. Knowledge of the rate of passage and viability of crop seed ingested by livestock is critical for good farm hygiene so that seeds are not inadvertently spread from the source paddock. Merino wethers were placed on a diet containing whole canola seed (10% total dry matter), and faeces were collected while canola was in the diet and for a further 6 days after canola was removed from the diet. Seed was found to pass through the wethers in less than 1 day, and reached a constant level after 2 days. When canola seed was removed from the diet, the majority of seed was passed during the first 2 days, but seed was excreted for up to 5 days. Seed germinability was reduced after 1 day, and further still after 2 days, but did not significantly decrease after this. While sheep are capable of excreting germinable canola seeds for up to 5 days after they were last included in the diet, use of a 7–10-day holding period will ensure that canola is not inadvertently spread beyond the grazed stubble paddock.