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Christmas Special: 

Rudolph and a lamb’s tale 


Wednesday, 9 December 2009. 5.30 p.m. – 6.45 p.m.

David Baird and Gerald Lincoln



Sheep usually have one lamb.

As in our own species a single offspring has the best chance of being born alive and being reared to become a healthy adult. This is achieved by restricting to one or two the number of eggs which are ovulated from the ovary each cycle.

Sheep are probably amongst the first animals to be domesticated by our early ancestors. Since then they have been selectively bred for certain chosen characteristics including the ovulation rate resulting in breeds which may have 3 or 4 lambs.

By studying the genetic factors which underly these breed differences it is possible to gain insight into the mechanisms which regulate the growth of follicles in women. In this way the tragedies associated with the birth of multiple babies could be avoided.

Timing of reproduction is equally important. Most species are seasonal breeders, fertile for only a limited period of the year – sheep and deer are examples. They use an internal clock mechanism (Nature’s Contraceptive) to restrict births to the best season. This usually applies to both sexes. Females fail to ovulate and males show regression of the testes and loss of sexual interest.

So let’s look at Rudolph at Christmas! He was at his peak in the rut in October, but now his testosterone levels have plummeted, he has cast his impressive antlers and he is rather sad. But maybe Rudolph is not a male after all, but a female, Rudolphine. She also has antlers unlike other species of deer, but she casts them in spring.

Female reindeer need their weapons in winter to compete with other females over holes they dig in the snow to reach the lichens – and to provide food for their offspring. So why is it that amongst mammals the two sexes often evolve different reproductive schedules, and why, you can ask, are humans not seasonal breeders? 

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