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Identification of Sperm Morphometric Subpopulations in Two Different Portions of the Boar Ejaculate and Its Relation to Postthaw Quality

FERNANDO SARAVIA

ANDERS JOHANNISSON

MARGARETHA WALLGREN

HERIBERTO RODRÍGUEZ-MARTÍNEZ

From the ^* Section of Animal Reproduction and Obstetrics, Department of Herd Health and Medicine, Faculty of Veterinary Medicine, University of Extremadura, Cáceres, Spain; the Division of Comparative Reproduction, Obstetrics and Udder Health, Department of Clinical Sciences and the Department of Anatomy and Physiology, Faculty of Veterinary Medicine and Animal Sciences, Swedish University of Agricultural Sciences, Uppsala, Sweden.

Correspondence to: Dr Fernando J. Peña, Section of Animal Reproduction and Obstetrics, Department of Herd Health and Medicine, Faculty of Veterinary Medicine, University of Extremadura, Avd de la Universidad s/n, 10071 Cáceres, Spain (e-mail: fjuanpvega{at}unex.es).

A statistical approach using sequentially principal component analysis (PCA), clustering, and discriminant analyses was developed to identify sperm morphometric subpopulations in well-defined portions of the fresh boar ejaculate. Semen was obtained as 2 portions (the first 10 mL of the sperm-rich fraction and the rest of the ejaculate, respectively) and frozen using a conventional protocol. Before freezing, an aliquot was used for computer-assisted sperm morphometry analysis (ASMA). Postthaw quality was evaluated using computer-assisted sperm analysis (CASA), and an annexin-V/PI assay evaluated sperm membranes. The PCA revealed that 3 variables represented more than 78% of the cumulative variance in sperm subpopulations. The clustering and discriminant analyses, based on 5780 individual spermatozoa, revealed the existence of 4 sperm subpopulations. The relative percentage of these subpopulations varied between boar and ejaculate portions. Linear regression models based on measured morphometric characteristics could account for up to 36% of the percentage of intact sperm membranes postthaw. The ASMA protocol used in our study was useful to detect subtle morphometric differences between spermatozoa, and the combination of this analysis with a multivariate statistical procedure gave new information on the biological characteristics of boar ejaculates that is not given by conventional sperm analysis.

     Key words: ASMA, sperm subpopulations, cryopreservation, cluster analysis

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