Original Research An Evaluation of Equine Sperm Chromatin After Exposure to Ambient Heat Stress Wendee C. Langdon a , Charles C. Love b , Sheila R. Teague b , Heidi A. Brady a , Samuel D. Prien a, c, * a Department of Animal and Food Sciences, Texas Tech University, Lubbock, TX b Department of Veterinary Large Animal Medicine and Surgery, Texas A&M University, College Station, TX c Department of Obstetrics and Gynecology, Texas Tech University Health Sciences Center, Lubbock, TX article info Article history: Received 10 June 2015 Received in revised form 2 September 2015 Accepted 4 September 2015 Available online 26 September 2015 Keywords: Assay Comparison DNA Fragmentation Heat Stallion abstract Several studies have evaluated the effects of excessive heat stress on chromatin damage; however, DNA damage due to ambient seasonal heat stress has yet to be evaluated. The objective of the present study was to evaluate the effects of natural heat stress on equine sperm chromatin structure by means of two tests: the sperm chromatin structure assay (SCSA) and Sperm-Halomax kit (Halo). Stallion semen samples were collected after a period of excessive heat load (31.05  C) and were compared with samples collected at lower ambient temperatures (14.26  C) to evaluate chromatin damage caused by ambient heat stress produced in the testes. The data indicate that there is no correlation between the SCSA and Halo assays (r ¼ 0.18 and F ¼ 0.48). Additionally, no correlation for ambient heat stress was observed for any of the applied techniquesdSCSA, Halo, and live:dead staining (P ¼ .2682, .4628, and .0377, respectively). These results suggest that ambient heat load has little effect on stallion chromatin damage. Other elements, such as relative hu- midity and heat index, were outside the realm of this study and should be assessed in future studies with a larger sample size. Ó 2015 Elsevier Inc. All rights reserved. 1. Introduction In the performance equine industry, stallions are generally selected for excellent pedigree, past perfor- mance, and performance of offspring. In contrast to other livestock, breeding stallions are not generally selected for reproductive soundness. However, reproductive efficiency increases the value of the stallion for commercial purposes, and extensive reproductive soundness exami- nations are used before the use of the stallion for breeding. Stallion Breeding Soundness Examinations (BSEs) involve elements of structural soundness, overall health, testicular measurements, cultures of preejaculation and post- ejaculation to test for infections, and a complete semen analysis [1]. A complete stallion BSE is important to pre- dict the potential fertility. A traditional semen analysis evaluates parameters such as volume, concentration, progressive motility, viability, and morphology [2]. The use of newer technology, such as the computer-assisted semen analysis (CASA), provides additional breakdown of progressive motility, which is useful when assessing the BSE [3]. Although these parameters serve as predictors for fertility, a stallion may still exhibit decreased fertility rates, or be classified as infertile, despite acceptable values in these parameters [4]. Furthermore, parameter may rapidly decrease with increased collection rates due to stallion popularity. Sperm chromatin, found within the head of the sper- matozoa cells, is comprised of densely packed DNA and heterogeneous nucleoproteins [5]. A number of factors have been shown to compromise sperm chromatin leading to decreased sperm viability, including an excessive heat load on the testes [6,7]. * Corresponding author at: Samuel D. Prien, Department of Animal and Food Sciences, Texas Tech University, M S 2141/Campus, Lubbock, TX 79409. E-mail address: samuel.prien@ttuhsc.edu (S.D. Prien). Contents lists available at ScienceDirect Journal of Equine Veterinary Science journal homepage: www.j-evs.com 0737-0806/$ – see front matter Ó 2015 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jevs.2015.09.005 Journal of Equine Veterinary Science 35 (2015) 960–965