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.

Responses to defoliation and fertiliser, corm development and chemical control of onion grass (Romulea rosea) in the Mediterranean environment of southern Australia

“…Since onion grass was introduced to Australia, it has become a weed that widely invades pastures, particularly native or low‐input improved pastures that is less frequently grazed in southern Australia (Nie et al, 2012). There have been reports (e.g., Bourke et al, 2008; McDonald & Eckel, 1968) that onion grass can cause serious health problems for sheep grazing infested pastures.…”

“…It has also spread to countries or regions such as New Zealand (Ghanizadeh & Harrington, 2019), Europe and California in the United States, with similar environmental conditions. Pastures with onion grass ingression have a rapid decline in feed production and nutritive value and can lead to health problems for grazing animals (McDonald & Eckel, 1968). There has been little research on the survival mechanism and growth of onion grass, how the plant responds to repeated defoliation and fertiliser application and the appropriate herbicides and time to control onion grass.…”

Cerebellar ataxia in sheep grazing pastures infested with Romulea rosea (onion grass or Guildford grass)

“…Romulea infertility is expressed as a failure to conceive, abortion and a low lambing percentage 2 . It is probably caused by the protracted ingestion of dry seed‐bearing plants in summer 2 .…”

“…2 It is probably caused by the protracted ingestion of dry seed-bearing plants in summer. 2 Romulea locomotor dysfunction, however, appears to occur independently of infertility and may be associated with grazing the plant at an earlier growth stage. For example, in 2001 in the Adelaide Hills district of South Australia, consumption of Romulea pastures throughout summer and autumn by a flock of November-December-joined Polwarth ewes, resulted in only 19 lambs being born to 84 ewes, but none of these ewes developed a locomotor dysfunction (Bourke, Ramsay and Muller, unpublished data).…”

“…Romulea infertility is expressed as a failure to conceive, abortion and a low lambing percentage 2 . It is probably caused by the protracted ingestion of dry seed‐bearing plants in summer 2 . Romulea locomotor dysfunction, however, appears to occur independently of infertility and may be associated with grazing the plant at an earlier growth stage.…”