Reproductive performance of Merino ewes grazing red clover (Trifolium pratense L.), improved pasture, or native pasture

Abstract

Each year, commencing in 1957, fine-wool Merino ewes that were born in 1954 grazed native and improved pasture from the time of weaning of their lambs (usually late January) until the end of the period when they were joined with rams (early June). For the remainder of each year, one group each grazed (A) improved pasture, (B) native pasture, and (C) a red clover (Trifolium pratense) pasture. Records of services, lambings, and birth and weaning weights of lambs were obtained each year until the final weaning in January 1963. Lambing, as a percentage of ewes joined, declined between 1957 and 1962 from 85–88% to 66% in groups A and B and to 25% in group C. An average of 89% of ewes that lambed each year conceived to the first service. This was not influenced by years or treatments. The total number of services recorded per group was greatest for group C. Birth weights were lighter and weaning weights were heavier for the lambs of group C when compared with those of groups A and B. Ewes that failed to lamb in any year tended to fail in successive years; hence the increases in flock infertility were due to ewes becoming sterile. A number of sterile ewes had cystic glandular hyperplasia of the endometrium.