The use of physiological traits in genetic selection for litter size in sheep
J. R. W. Walkley,Charles Smith +1 more
TL;DR: The objective was to quantify and compare the genetic responses by direct selection on litter size, by indirect selection through a physiological trait and by combined selection, combining litter size and the physiological trait in a selection index.
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Abstract: Summary. The objective was to quantify and compare the genetic responses by direct selection on litter size, by indirect selection through a physiological trait and by combined selection, combining litter size and the physiological trait in a selection index. Three kinds of physiological trait were considered, male sex-limited (e.g. testes size), female sex-limited (ovulation rate) and traits measurable in both sexes (gonadotrophin levels). The results are presented graphically and cover a wide range of possible situations and show the size of the responses for different parameters of the physiological trait. There is usually scope for improvement in the rate of response with combined selection, and also in special cases (high heritability and genetic correlation) with indirect selection. The increases in predicted response may range from zero to two or three times the direct response, depending on the genetic parameters. However, the need for reliable estimates of the genetic parameters is stressed, because the predicted responses might otherwise be overestimated and the selection effort misplaced.
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Citations
A review of factors that impact on the capacity of beef cattle females to conceive, maintain a pregnancy and wean a calf—Implications for reproductive efficiency in northern Australia
TL;DR: A review of factors that may impact on the capacity of beef cattle females, grazing semi-extensive to extensive pastures in northern Australia, to conceive, maintain a pregnancy and wean a calf was conducted and conclusions and recommendations to minimise reproductive inefficiencies based on current knowledge are presented.
176
Reproductive characteristics of Ethiopian highland sheep. II. Genetic parameters of semen characteristics and their relationships with testicular measurements in ram lambs.
TL;DR: There was improvement in all semen and spermatozoa traits with age, the means at 12 months being consistently superior to values at 6 and 9 months of age, and differences were attributed primarily to nutrition.
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Genetic variation and covariation for ewe reproduction, lamb growth, and lamb scrotal circumference in a fall-lambing sheep flock
S A al-Shorepy,David R. Notter +1 more
TL;DR: Estimated genetic correlations revealed no major genetic antagonisms with ability to lamb in fall and genetic correlations among body weights ranged from .77 to unity.
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Reproductive Characteristics of Ethiopian Highland Sheep. I. Genetic Parameters of Testicular Measurements in Ram Lambs and Relationship With Age at Puberty in Ewe Lambs
TL;DR: SC was suggested as the most appropriate selection candidate for the genetic improvement of both male and female reproductive performance in two fat-tailed sheep breeds, indigenous to the Ethiopian highlands.
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Heritabilities and genetic correlations of body weight, testis growth and ewe lamb reproductive traits in crossbred sheep
S. L. Fossceco,David R. Notter +1 more
TL;DR: Heritabilities (h2) and genetic correlations (rc) involving body weights, measures of testes size and ewe lamb reproduction were calculated using 953 spring-born lambs produced during formation of a three-breed composite population containing 0·50 Dorset,0·25 Rambouillet and 0·25 Finnish Landrace breeding.
52
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TL;DR: The pattern of changes of the genetic covariance between two characters on selection was examined in an effort to explain the asymmetry of correlated responses in two traits, or of the same trait in two environments, frequently observed in experimental results.
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Design and efficiency of selection experiments for estimating genetic parameters.
TL;DR: Mass selection is likely to be best for comparing response from alternative selection programmes or populations, and several methods of estimating heritability are compared, of these the realised heritability has least variance.
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Assessment of new and traditional techniques of selection for reproduction rate
B.M. Bindon,L.R. Piper +1 more
- 01 Jan 1979
TL;DR: This chapter assesses the problems of direct selection for these components of sheep reproduction rate and reviews indirect approaches under investigation.
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