Please cite this article in press as: Garde, E., et al., Effects of surgical and chemical sterilization on the behavior of free-roaming male dogs in Puerto Natales, Chile. PREVET (2015), http://dx.doi.org/10.1016/j.prevetmed.2015.11.011 ARTICLE IN PRESS G Model PREVET-3917; No. of Pages 15 Preventive Veterinary Medicine xxx (2015) xxx–xxx Contents lists available at ScienceDirect Preventive Veterinary Medicine j o ur na l ho me page: www.elsevier.com/locate/prevetmed Effects of surgical and chemical sterilization on the behavior of free-roaming male dogs in Puerto Natales, Chile E. Garde a,b,∗ , G.E. Pérez a,b , R Vanderstichel c , P.F. Dalla Villa d , J.A. Serpell e a The Global Alliance for Animals and People, Pasaje Los Arrayanes 333, Valdivia 5110624, Chile b Veterinarians without Borders/Vétérinaires sans Frontiéres Canada c Department of Health Management, Atlantic Veterinary College, University of Prince Edward Island, 550 University Avenue, Charlottetown, PEI C1A 4P3, Canada d Human–Animal Relationship and Animal Welfare Laboratory—Istituto Zooprofilattico Sperimentale dell’Abruzzo e del Molise “G. Caporale”, Campo Boario, 46100 Teramo, Italy e Department of Clinical Studies—Philadelphia, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA a r t i c l e i n f o Article history: Received 18 May 2015 Received in revised form 4 November 2015 Accepted 18 November 2015 Keywords: Free-roaming dogs Behavior Testosterone Zinc-gluconate Sterilization Factor analysis a b s t r a c t Population management of free-roaming domestic dogs (Canis lupus familiaris) is of interest due to the threat these animals pose to people, other animals and the environment. Current sterilization procedures for male dogs include surgical and chemical methods. However, little is known about how these proce- dures affect their behavior. The primary objective of this study was to investigate changes in selected behaviors following chemical and surgical sterilization in a male free-roaming dog (FRD) population in southern Chile. We also examined the association between serum testosterone levels and behaviors thought to be influenced by circulating androgens. A total of 174 dogs were randomly assigned to either a surgical or chemical sterilization group, or a control group. At the onset of the intervention period, 119 dogs remained and 102 dogs successfully completed the study. Each dog was monitored pre- and post-intervention using video recordings, GPS collars, and blood samples for the measurement of testos- terone. Analysis of behavior revealed that surgically castrated dogs showed no reduction of sexual activity or aggression when compared to their pre-intervention behavior. Chemically sterilized dogs showed a statistically significant increase in dog-directed aggression, but no change in sexual activity. There was no change in home range size in any groups between the pre- and post-intervention measurement. We found no consistent association between levels of serum testosterone concentration and behavioral changes in any of the groups. This study presents the first detailed behavioral observations following surgical and chemical sterilization in male FRDs. The information generated is highly relevant to communities struggling with the control of FRDs. Complementary studies to further our understanding of the effects of male sterilization on the behavioral and reproductive dynamics of FRD populations are needed. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Population control and management of free-roaming domes- tic dogs (Canis lupus familiaris) is gaining in interest because of the threat they pose to public, animal and environmental health and welfare (Butler et al., 2004; Morgan and Palmer, 2007; Otranto et al., 2009; Dalla Villa et al., 2010; McKenzie, 2010; Garde et al., 2013a). In developing countries, where the issue is more promi- nent (Dalla Villa et al., 2010), sterilization is the principal strategy promoted to halt reproduction and/or to modify undesirable behav- ∗ Corresponding author. E-mail address: elena.garde@thegaap.org (E. Garde). iors. However, sterilization efforts are usually focused on female dogs because it is considered a more effective population control approach when resources are limited, and/or where there is cul- tural opposition to the removal of the testes in male dogs (Levy et al., 2008; McKenzie, 2010). There is increasing public pressure in some countries to include male dogs in sterilization campaigns in the hope that it will reduce reproduction and undesirable traits such as aggression and roaming. This is creating an imminent need to evaluate how different methods of sterilization of male dogs may impact their behavior. A series of studies published primarily between the 1970s and 1990s suggested that surgical castration of male dogs improved their behavior with regards to inter-male aggression, urine- marking, roaming and mounting (Hart, 1968, 1974, 1979; Le Boeuf, http://dx.doi.org/10.1016/j.prevetmed.2015.11.011 0167-5877/© 2015 Elsevier B.V. All rights reserved.