Effect of time of joining and rate of stocking on the production of Corriedale ewes in southern Victoria. 5. Ovulation rate and embryonic survival

Abstract

In the final five months of an experiment which had lasted from November 1967 to June 1971 a study was made of the ovulation rate and embryonic survival in a flock of 540 five-year-old Corriedale ewes grazing annual pasture in southern Victoria. Ewes were stocked at 5, 7 1/2 or 10 ewes ha-1, and were joined with rams for six weeks beginning at either February 8 or April 19, 1971. A comparison with actual lambing data in 1970 was made. Ewes stocked at 5 ewes ha-1 had a higher ovulation rate and estimated lambing rate (based on embryos surviving to day 28) than those stocked at 7 1/2 or 10 ewes ha-1. Ovulation rate was higher for ewes of high liveweight than for ewes of low liveweight among those stocked at 7 1/2 and 10 ewes ha-' but not among those stocked at 5 ewes ha-1. Ewes joined in April had a higher ovulation rate and estimated lambing rate than ewes joined in February. There was no significant interaction between joining time and stocking rate on estimated lambing rate which was in contrast to the previous year 1970, when increased stocking rate reduced the number of lambs born per ewe from the February joining. Embryonic survival was greater among ewes joined in February and stocked at 7 1/2 ewes ha-1. There was no difference between stocking rates in embryonic survival among ewes joined in April. There was a trend for fewer twin ova to be lost when shed in April than in February.