A plan for breeding ewe lambs: expose early or wait?

Ewes and ewe lambs on stockpiled pasture. Photo credit: C. B. Moore

In the midst of peak sheep breeding season, many farmers are faced with the tough call — do you put the rams in with the ewe lambs now, or wait until the ewe lambs are older? Like most production-related questions, the answer is: it depends.

A ewe lamb that gives birth around her first birthday will be a more productive ewe in her lifetime, producing more lambs total than a ewe lamb bred as a  yearling. Assuming we’re not about to wait an entire year, though, is there a benefit to waiting a few extra months and lambing out ewe lambs at 12 months versus say, 15 to 18 months?

For that discussion we go to Dr. Richard Ehrhardt, ruminant animal extension specialist with Michigan State University. Earlier this month, he spoke on the topic of ewe lamb breeding strategies at the Ontario Sheep Convention. Given the audience’s interest, it’s clear this is a hot topic for many sheep producers.

Ehrhardt says that there are several factors that go in to a successful ewe lamb conception — and that the ewe’s birth month has a huge impact on when she’ll first experience estrus. Because sheep are seasonal (some breeds more than others), ewe lambs will experience their first heat closer to the shortest day of the year. It means that a May-born ewe lamb may actually reach sexual maturity at about the same time of year as a February-born ewe lamb, allowing for a much smaller time frame from birth to first-lambing.

That said, ewe lambs must be a sufficient size before they’ll experience a heat cycle, and that all has to do with a certain level of fat, Ehrhardt explains. Most ewe lambs need to be about 70% of their mature size before they’re likely to conceive. For this reason, a September-born ewe lamb, for example, is still susceptible to day length and needs to reach a sufficient size before breeding. Because of this, fall-born ewe lambs are often the oldest of the group before they reach sexual maturity. (Text continues below)

Ehrhardt says that there are differences in conception rates, lambing percentages, and total weaned lambs between slightly younger and older ewe lambs. When comparing 12 month-old vs 16 month-old ewe lambs, the older ewe lambs had somewhat better conception and lambing rates, but the biggest difference was at weaning. The theory is that a ewe lamb that experiences one or more heats prior to actually being bred has a chance to develop more mammary tissue, thus setting her up to raise more or larger lambs.

If you’ve kept back ewe lambs and by March have ended up with crummy conception rates, do you expose them again or do you cull?

When it comes to culling decisions, Ehrhardt says that if breeding in-season, with ewe lambs at 70% of mature body weight, and over two heats, anything still open at scanning (done between day 30-45 after ram removal) gets shipped. The reasoning is two-fold: one, she’s been given the best conditions for conception and didn’t catch, which could indicate lower overall fertility; and, she’s also still young enough to be sold as a market lamb — an open ewe lamb still has good market value.

More from Dr. Richard Ehrhardt: Focus on ram management for out of season success

See this interview as filmed by Sandi Brock, Sheepishly Me

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