Acta Veterinaria Scandinavica Research Morphology and head morphometric characters of sperm in Thai native crossbred stallions Kanittha Phetudomsinsuk†1,2, Kaitkanoke Sirinarumitr*†1, Aree Laikul†1 and Anuchai Pinyopummin†1 BioMed Central Open Access Address: 1Faculty of Veterinary Medicine, Kasetsart University, Kamphaeng Saen Campus, Nakhon Pathom 73140, Thailand and 2Center for Agricultural Biotechnology, Kasetsart University, Kamphaeng Saen Campus, Nakhon Pathom 73140, Thailand Email: Kanittha Phetudomsinsuk - fvetktp@ku.ac.th; Kaitkanoke Sirinarumitr* - fvetkns@ku.ac.th; Aree Laikul - fvetarl@ku.ac.th; Anuchai Pinyopummin - fvetacp@ku.ac.th * Corresponding author †Equal contributors Published: 22 October 2008 Acta Veterinaria Scandinavica 2008, 50:41 doi:10.1186/1751-0147-50-41 This article is available from: http://www.actavetscand.com/content/50/1/41 Received: 4 July 2008 Accepted: 22 October 2008 © 2008 Phetudomsinsuk et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract Background: One of the semen quality parameters use to determine fertility is the percentage of sperm that express normal morphology. Sperm head morphometry is also correlated with fertility. The objectives of this study were 1) to investigate the sperm morphology and normal sperm head morphometry of Thai native crossbred stallions, and 2) to compare our results with the characteristics of proven fertile sperm from purebred stallions. Methods: Semen samples were collected monthly from nine stallions, of which five were Thai native crossbred (T) and four were purebred of proven fertility (F: F1 was a Standard-bred; F2 was a Warm- blood; F3 and F4 were Thoroughbreds). All the animals were aged between 5 and 12 years. Sperm morphological examination was performed using formaldehyde-fixed samples under phase-contrast microscopy (1000×). Normal sperm head morphometry characteristics were measured by Computer- Assisted Semen Analysis (Hamilton Thorne, USA.) after applying the Harris' haematoxylin staining technique. Results: The percentages of morphologically normal and abnormal sperm varied among individual stallions in both the T and F groups. The mean percentage of morphologically normal sperm was not significantly different (P > 0.05) between T and F stallions (mean ± SE, 49.7 ± 1.3 and 48.1 ± 2.8, respectively). A comparison between the T and F sperm heads revealed that all the dimensional parameters were significantly different (P < 0.05). The coefficients of within-animal variation (CVs) ranged from 2.6 (shape factor 1) to 7.5 (elongation) and 2.9 (shape factor 1) to 8.1 (elongation) in T and F, respectively. In the case of the T group, those sperm head parameters that featured a low within-animal CV and a high between-animal CV were perimeter (2.9, 19.1), shape factor 1 (2.6, 25.8) and shape factor 3 (3.8, 32.0). In the case of the F group, only shape factor 1 (2.9, 26.1) featured such characteristics. Conclusion: We found variability in the percentage of morphologically normal and abnormal sperm, as well as in sperm head dimensions among Thai native crossbred stallions, and these results were similar to those of purebred stallions. Our findings demonstrate that the heads of the T sperm specimens were larger and rounder than that of the F sperm. Perimeter, shape factor 1 and shape factor 3 could be used as parameters for the identification of individual T stallions based on a sperm sample. Page 1 of 9 (page number not for citation purposes)