Animal Reproduction Science 101 (2007) 18–27 Relationship between bovine fertility and the number of spermatozoa penetrating the cervical mucus within straws Muzaffer Tas ¸ a,∗ , Suleyman Bacinoglu b , ¨ Um¨ ut Cirit b , ¨ Ozen Banu ¨ Ozdas ¸ b , Kemal Ak b a Department of Obstetrics and Reproduction, Faculty of Veterinary Medicine, Dicle University, 21280 Diyarbakir, Turkey b Department of Reproduction and Artificial Insemination, Faculty of Veterinary Medicine, Istanbul University, 34320 Istanbul, Turkey Received 23 May 2006; received in revised form 8 August 2006; accepted 17 August 2006 Available online 12 September 2006 Abstract In this study, by using a recently developed test technique, the relationship between the total spermatozoa number penetrating determined sites of bovine cervical mucus in straws and potential fertility of bulls, and other spermatological characteristics were investigated. Furthermore, we aimed to determine the effect on the test results, of two different incubation temperatures (37 and 41 ◦ C) and two sperm penetration distance ranges (PDRs). Frozen semen samples of six Holstein bulls were used in the study. The bulls were divided into two fertility groups (high and low fertility) according to the “non-return rates” (NRR). For the penetration test, cervical mucus was drawn into transparent plastic straws and incubated with semen at 37 and 41 ◦ C for 15 min. After the incubation, straws were frozen in liquid nitrogen vapour and stored at −20 ◦ C. On the evaluation day, concentrations of spermatozoa penetrated to the PDRs, each of which was 2.5 mm, between 32.5 and 35 mm (first penetration distance range, PDR1), and 50 and 52.5 mm (second penetration distance range, PDR2) distance in the straws from the open end, were measured. When compared with the low fertility group, bulls from the high fertility group showed a higher number of spermatozoa at the determined PDRs, and a significant positive correlation was found between the total number of spermatozoa at the penetration distances and the NRR scores of the bulls. © 2006 Elsevier B.V. All rights reserved. Keywords: Bull semen; Cervical mucus; Penetration test ∗ Corresponding author. Tel.: +90 412 248 80 20x8622; fax: +90 412 248 80 21. E-mail address: mtas@dicle.edu.tr (M. Tas ¸). 0378-4320/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.anireprosci.2006.08.020