Explaining Seasonal Breeding in Sheep with Emeritus Professor David Notter

Dr David Notter spent 25 years looking into the seasonality of breeding sheep and how to reduce it via genetic selection. We are very lucky to have him as a guest on the podcast today to share his wisdom on all things sheep breeding.

In 1977, the American Sheep Industry Association identified a pressing challenge: reducing seasonality in ewe breeding. Virginia Tech became the base for this research, where they aimed to create a flock of sheep capable of breeding throughout the year.

They assembled a crossbred population consisting of half-Dorset, a quarter Rambouillet and a quarter Finn sheep. Initially, the ewes in the population had a pregnancy rate of about 50% during May and June (out of season for the northern hemisphere). While not an ideal figure, it was a starting point; within five years, the flock had reached 85%. By the end of the project, these ewes were breeding as successfully in summer as those being bred in the autumn.

One fascinating aspect of the study was the role of the 'ram effect'. Although initially expected to play a significant role in the success of the project, it turned out to have less influence than anticipated. Rather, the ewes themselves had an influence, explains David. “Just like you get a ram effect, you can also get a ewe effect by cohabiting. If you want to try and breed a bunch of blackface sheep, I would put them with a bunch of cycling Merinos or Dorsets, if you had them. We know it made a difference.”

Towards the end of the project, after years of selection pressure, some ewes had exceptional reproductive capacity. “These ewes successfully lambed around the shortest day and, approximately 60 days later, conceived during lactation,” explains David. He also explains that during the first few years, this wasn’t always the case with ewes absorbing the fetus far more regularly.

They also had issues with out-of-season lambs being slower to grow, which David believes is due to less-than-optimum uterine conditions during gestation.

David’s experience in this field is second to none and the wealth of knowledge in this podcast is phenomenal. Whether you’re contemplating out-of-season breeding, or you just want to know more about the oestrus cycle of your sheep, this podcast is not one to miss.

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