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Variability of litter size of french sheep breeds following natural or induced ovulation

Published online by Cambridge University Press:  02 September 2010

L. Bodin  and
J. M. Elsen
L. Bodin
Affiliation:
Institut National de la Recherche Agronomique, Station dAmelioration Genetiques des Animaux, Centre de Recherches de Toulouse, BP 27, 31326 Castanet Tolosan, France
J. M. Elsen
Affiliation:
Institut National de la Recherche Agronomique, Station dAmelioration Genetiques des Animaux, Centre de Recherches de Toulouse, BP 27, 31326 Castanet Tolosan, France
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Abstract

The assumption that observed values for litter size result from a set of thresholds which impose a discontinuity to the visible expression of a continuous underlying variate has been tested using data from the French sheep recording scheme: 629 724 natural lambings for 32 different pure breeds and 66 379 litters obtained after synchronization treatment in 15 breeds. Frequencies of single, twin, triplet and higher-order births varied regularly with litter size within each fecundation type. The coefficient of variation of litter size was remarkably constant from breed to breed under both natural (0·35 to 0·40) and induced lambings for which it was higher (0·40 to 0·45). The regression of the difference between the first two thresholds of an underlying normally distributed variate on prolificacy was slowly negative for natural fecundation, but not significant for induced fecundation. A significant effect of fecundation type was found, resulting in a lower incidence of induced than of natural twin litters for the same level of prolificacy. Multivariate polynomial regression of frequencies on natural and induced prolificacy was used to predict expected frequencies of litter size and the proportion of lambs of each birth type.

Type
Papers
Information
Animal Production , Volume 48 , Issue 3 , June 1989 , pp. 535 - 541
Copyright
Copyright © British Society of Animal Science 1989

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