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Effects of age and its relationship with body size on reproductive performance in Scottish Blackface ewes

Published online by Cambridge University Press:  02 September 2010

R. G. Gunn ,
J. M. Doney ,
W. F. Smith  and
D. A. Sim
R. G. Gunn
Affiliation:
Hill Farming Research Organisation, Bush Estate, Penicuik, Midlothian EH26 0PY
J. M. Doney
Affiliation:
Hill Farming Research Organisation, Bush Estate, Penicuik, Midlothian EH26 0PY
W. F. Smith
Affiliation:
Hill Farming Research Organisation, Bush Estate, Penicuik, Midlothian EH26 0PY
D. A. Sim
Affiliation:
Hill Farming Research Organisation, Bush Estate, Penicuik, Midlothian EH26 0PY
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Abstract

On a hill farm, the reproductive performance of Scottish Blackface ewes increases annually with increasing age up to 6 years and is positively related to pre-mating live weight. A group of Scottish Blackface ewe lambs was, from 5 months of age, preferentially managed over a 2-year period to accelerate the achievement of mature size, in order to study the relative importance of age and size to reproductive performance. Ovulation rate and early embryo mortality of these ewes at 31 months of age were compared with those of adult ewes of similar body size and condition at 79 months of age which had been reared conventionally in the same hill flock. Two comparisons were made, one between different age groups in the same year and the other retrospectively between different ages of the same age group. In the first comparison, the adult ewes had a slightly greater reproductive response which suggested a small effect of age per se but there was also the possibility of a genetic difference. In the second comparison, there was no difference in ovulation rate or potential lambing rate per pregnant ewe, but a trend towards greater wastage of twin-shed ova in the heavier and fatter younger ewes again suggested a small effect of age. At both ages, however, these ewes performed close to their adult genetic potential which suggested that the treatment of the young ewes was sufficient to overcome most of the limitations associated with age or size. Reproductive performance normally associated with young animals is therefore mainly an expression of their size relative to their maturity and the removal of the size limitation by higher levels of nutrition and more rapid growth can largely eliminate their poorer performance.

Type
Research Article
Information
Animal Production , Volume 43 , Issue 2 , October 1986 , pp. 279 - 283
Copyright
Copyright © British Society of Animal Science 1986

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References

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