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Relationship between sex ratio and time of insemination according to both time of ovulation and maturational state of oocyte

Published online by Cambridge University Press:  05 April 2001

A. Gutiérrez-Adán
Affiliation:
Departmento de Reprodución Animal y Conservación de Recursos Zoogenéticos, INIA, Ctra de la Coruña Km 5.9, Madric 28040, Spain
Pérez-Garnelo
Affiliation:
CERSYRA de Valdepeñas, Consejería de Agricultura y Medio Ambiente de Castilla-La Mancha, Ciudad Real 13300, Spain
J. Granados
Affiliation:
Departmento de Reprodución Animal y Conservación de Recursos Zoogenéticos, INIA, Ctra de la Coruña Km 5.9, Madric 28040, Spain
J.J. Garde
Affiliation:
Departmento Ciencia y Tecnología Agroforestal, Universidad Castilla-La Mancha, Campus Universitario SN, Albacete 02071, Spain
M. Pérez-Guzmán
Affiliation:
CERSYRA de Valdepeñas, Consejería de Agricultura y Medio Ambiente de Castilla-La Mancha, Ciudad Real 13300, Spain
B. Pintado
Affiliation:
Departmento de Reprodución Animal y Conservación de Recursos Zoogenéticos, INIA, Ctra de la Coruña Km 5.9, Madric 28040, Spain
J. De La Fuente
Affiliation:
Departmento de Reprodución Animal y Conservación de Recursos Zoogenéticos, INIA, Ctra de la Coruña Km 5.9, Madric 28040, Spain

Abstract

The aim of this study was to explore how some reproductive methodologies may affect the sex ratio. We first confirmed the association between the maturation stage of bovine oocytes at the time of in vitro fertilisation (IVF) and the sex ratio of in vitro-derived embryos. Secondly, we studied whether the time of insemination, prior to or after ovulation, could alter the sex ratio in sheep. In the first experiment, bovine oocytes were matured in vitro for 16 h; then oocytes were either fertilised in vitro immediately after extrusion of the first polar body or IVF was delayed for 8 h. The proportion of cleaving embryos and their development to the 8-cell stage was enhanced with delayed insemination. Moreover, delaying IVF produced a male-to-female sex ratio of 1.67:1.00, which was significantly different from the expected 1:1 ratio (p < 0.05), whereas more female embryos were produced when oocytes were fertilised in vitro immediately after polar body extrusion (sex ratio of 1.00:0.67; p < 0.05). In the second experiment, 380 ewes were inseminated at different times before or after ovulation, producing 537 lambs. Significant differences in the sex ratio were obtained when we compared the sex of the offspring of ewes inseminated during the 5 h preceding ovulation (more females) with those inseminated during the 5 h after ovulation (more males). Our results suggest that the differential ability of X- or Y-bearing spermatozoa to fertilise oocytes depending either on time of insemination or oocyte maturation state, may be due, at least partially, to ‘intrinsic’ differences in the physiological activity of X- or Y-bearing spermatozoa before fertilisation.

Type
Research Article
Copyright
1999 Cambridge University Press

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