Disclaimer: There is no “right way” when it comes to breeding; this is just an account of how we go about our breeding program.
Our ewes are fall breeders, cycling every 16-18 days during the breeding season. As the day length decreases, melatonin is secreted. This triggers the brain to produce gonadotropin releasing hormones, causing the first ewes start to cycle. We like to lamb in the month of April and since the gestation period is approximately 5 months, we breed in November!
Since we prefer to concentrate our lambing into a shorter, more predictable time frame, we synchronize our ewes’ reproductive cycles. If we didn’t have enough unrelated rams this would not be feasible. In other words, if you had 40 ewes synchronized to come into heat at the same time, one ram would obviously not cover them. We don’t go over 6-8 ewes per ram, but you could push it to 10.
We synchronize our ewes using CIDR’s (controlled internal drug release). They are small progesterone secreting devices that are placed intravaginally with a little plastic “tail” that remains outside the vulva so you can pull it out after about 14 days. Say you want to begin lambing on April 15th; count back 147-150 days, give or take, and that’s when you want mating to occur. The CIDR’s are inserted in all of the ewes. They then move into a progesterone phase. At 14 days, the CIDR’s are removed.
The rapid progesterone drop triggers an estrogen response, resulting in the ewes coming into heat around 24-48 hours later. Therefore, you not only count back about 150 days, but also about 14-16 more days for the CIDR, and give or take 2 days for the heat cycle to start. Because the ewe cycles every 16-18 days you can predict the next cycle if the first breeding doesn’t take.
We’ll keep the ram in with his group for 2 cycles. Approximately 40 days after the first breeding, we pull blood from all the ewes and serum test for pregnancy. If there’s a “negative” ewe, we’ll retest at 40 days after the second cycle.
It’s really great to ‘know’ when lambing is going to occur. In the third trimester, we’ll give the ewes a CDT vaccine in hopes of better passive transfer of tetanus protective antibodies since we don’t vaccinate the lambs with CDT until 3-4 weeks of age.
Also, an important note regarding “flushing”; This increases the amount of food/energy available to the ewes before and during breeding season. Three weeks before introducing the rams, the ewes are getting one pound per head per day of a balanced grain rotation, along with their high quality hay. This continues through the breeding period. This can increase lambing rates by 10-20%!
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