Animal Reproduction Science 99 (2007) 395–400 Short communication Effect of egg yolk and seminal plasma heparin binding protein interaction on the freezability of buffalo cauda epididymal spermatozoa L.P. Singh, Hiron M. Harshan ∗ , M.R. Ansari Division of Animal Reproduction, Indian Veterinary Research Institute, Izatnagar, Bareilly, UP 243122, India Received 20 May 2006; received in revised form 7 August 2006; accepted 10 August 2006 Available online 17 August 2006 Abstract Egg yolk is routinely used in most of the extenders for cryopreservation of semen, but mechanisms of protection of spermatozoa by egg yolk are not very clear. Investigations with buffalo cauda epididymal sperm have shown that seminal plasma heparin binding proteins have detrimental effects during semen cryopreservation. The present study was conducted to investigate the effect of egg yolk on the detrimental effects of heparin binding proteins during cryopreservation of buffalo cauda epididymal spermatozoa. The results indicated that egg yolk was able to reduce the heparin binding proteins mediated cryoinjury in spermatozoa. One of the mechanisms of protection of spermatozoa from cryoinjury by egg yolk may be due to the inhibition of deleterious actions of heparin binding proteins on the spermatozoa. © 2006 Elsevier B.V. All rights reserved. Keywords: Buffalo; Cauda epididymal spermatozoa; Egg yolk; Heparin binding proteins; Seminal plasma; Cryopreser- vation 1. Introduction Hen’s egg yolk (EY) is an integral part of the extenders used for bovine semen. The low-density lipoprotein fraction (LDF) of EY appears to be responsible for protection of sperm against freezing damages (Moussa et al., 2002). Many of the hypotheses put forward for mechanisms of sperm protection by LDF suggest an association of LDF with sperm membranes (Foulkes, 1977; Cookson et al., 1984) while others suggest that EY-LDF prevents the loss of membrane phospholipids (Parks ∗ Corresponding author. Tel.: +91 9412067563; fax: +91 581 2304058. E-mail address: hiron@rediffmail.com (H.M. Harshan). 0378-4320/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.anireprosci.2006.08.018