Diet selection in relation to onion grass and a sheep breeding problem in Victoria

Abstract

These studies were made in the Inverleigh district of Victoria where a sheep breeding problem has occurred among summer-mated ewes in some years since 1947. The possibility of onion grass (Romulea rosea L.) poisoning being responsible for this problem was investigated. The botanical composition of the diet selected by four sheep, fitted with oesophageal fistulas and grazing an onion grass dominant pasture on a problem property, was determined approximately every two weeks during the late summer and autumn of two years. One year (1965) was a problem year and the other year (1966) was a non-problem year for sheep reproduction on this property and in this district. The experimental sheep ate appreciable amounts of both dry and green onion grass, especially in the late summer and immediately after the autumn rains. The mean percentage of dry onion grass in the diet before the autumn break was 20 in 1965 and 31 in 1966 ; and after the autumn break the mean per cent of green onion grass was 16 in 1965 and 28 in 1966. Overall, the sheep did not show a dietary preference for onion grass as twice these levels were present in the dry or green pasture species. The major difference in onion grass intake between the two years was that, because of the late autumn break in 1965, the fistulated animals ate dry onion grass (and onion grass seed) for six weeks longer than in 1966.