Changes in the median lambing dates and lambing pattern with variation in time of joining and breed of teasers

Abstract Median lambing dates and lambing patterns of ewes joined on 3 March after 14 days' teasing with Romney teasers were compared with those of ewes teased with Dorset teasers and ewes joined on 17 March after teasing for 14 days or 28 days with Romney teasers. Data were also obtained on the percentage of ewes mated in the first 14 days of entire joining (Period 1), conception rates in the first and second 14 days ofentirejoining (Periods 1 and 2), and percentage of ewes lambing. Two flocks of ewes grazed on hill country were used; one consisted of various breeds (Flock A) and the other of ewes selected for various production characters (Flock B). Delaying joining until 17 March caused median lambing dates to be only 4–8 days later, but gave a more concentrated lambing. The 14 days delay injoining increased percentage of ewes mated in Period 1 by 27–58% and conception rate in this period by 12–22%. In Flock B percentage of ewes lambing was increased by 6–8%. Increasing the teasing period from 14 days to 28 days did not further improve reproductive performance. Median lambing dates were 1–5 days earlier after teasing with Dorset teasers. Percentage of ewes mated in Period 1 increased by 8–33%, and in Flock B conception rate increased 13% in this period. Conception rates increased from Period 1to Period 2 for the ewes joined on 3 March but not for thosejoined on 17 March. Period 1 of ewes joined on 17 March and Period 2 of those joined on 3 March coincided and the conception rates were similar. These results confirm that the increase in conception rate over the joining period reflects the seasonal change in ewe fertility.