VARIATION BETWEEN MERINO EWES IN PASTURE INTAKE .1. BETWEEN FLOCK DIFFERENCES AND SOME ENVIRONMENTAL SOURCES OF VARIATION

Pasture intake of Merino breeding ewes was measured by marker dilution using chromium sesquioxide. Measurements were made on approx. 300 ewe s in four seasons associated with stages of the annual reproductive cy cle in each of 2 years, The ewes represented 15 separate randomly-bred bloodlines (flocks) in an experiment to determine the extent of envir onmental and genetic sources of variation. Mean digestible organic mat ter intakes (DOMI) were 623, 734, 1123 and 779 g/day in autumn (early pregnancy), winter (late pregnancy), spring (mid-lactation) and summer (post-weaning), respectively, The repeatability of daily estimates of DOMI within measurement periods varied from 0.32 to 0.47 across seaso ns, while the repeatability across periods was lower (0.09 to 0.27), F lock differences in DOMI were significant in all seasons except spring . In all seasons DOMI was positively related to liveweight and was neg atively associated with ultrasonic fat depth. After adjusting for live weight and fat differences, between-flock variation in DOMI was small relative to that of wool growth and liveweight.