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Submitted on: 13 April 1999.
Revised on: 07 August 1999.
Accepted on: 02 October 1999.
___________________ANIMAL REPRODUCTION SCIENCE---ELSEVIER
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Submitted on: 19 March 1999.
Revised on: 28 June 1999.
Accepted on: 25 August 1999.
___________________ANIMAL REPRODUCTION SCIENCE---ELSEVIER