R.L. Fields1, D.J. Moot1, G.K. Barrell1
1 Lincoln University, Faculty of Agriculture and Life Sciences, PO Box 85084, Lincoln 7647, New Zealand, www.lincoln.ac.nz,
The response of coumestrol to water stress was assessed in two lucerne cultivars ‘Wairau’ and ‘Kaituna’. Coumestrol content of lucerne is of importance because its ingestion by ewes prior to and during the mating period can decrease ovulation rate. Some farmers take the conservative approach of removing animals from wilted lucerne during this period in case of elevated coumestrol, but the evidence for or against this practice is lacking. This experiment found that coumestrol content was 2.2 mg/kg DM in well-watered lucerne and was not elevated in wilted lucerne (1.3 mg/kg DM). After two weeks coumestrol in well-watered lucerne decreased to 0.95 mg/kg DM, while a slight increase to 3.0 mg/kg DM occurred in senesced plants but remained below the levels expected to affect ewe reproduction. This result indicates that farmers can safely graze ewes on wilted lucerne for mating.