We have investigated the effect of immunization against gonadotropin releasing hormone (GnRH) using a commercial canine GnRH vaccine on testosterone concentration, testicular volume, testicular histology, and intermale behavior in intact male llamas and alpacas. Llamas ( ) and alpacas ( ) were either immunized (received 3？mL of vaccine given intramuscularly) or treated as controls (received 3？mL of sterile diluent given intramuscularly) at 0, 3, and 6 weeks. Blood samples and testicular volume measurements were taken at 0, 3, 6, 9, and 12 weeks. Owner surveys grading behavior at 0 and 12 weeks were received for 14 llamas. Two llamas at each time point undergoing the vaccination procedure were also castrated for testicular histological examination. Vaccinated animals elicited a GnRH antibody titer, and there was a significant decrease in testosterone concentration and testicular volume when compared with control animals. Intermale aggressive behavior was also significantly decreased in the surveyed llamas. However, histological examination revealed no significant changes. GnRH immunization using the canine GnRH vaccine may be an effective method for reducing intermale aggression in llamas and alpacas by decreasing circulating testosterone concentrations but cannot be recommended as an immunosterilant because of its lack of efficacy in interrupting spermatogenesis. 1. Introduction The cohousing of intact male llamas and alpacas is a common farm arrangement for camelid owners in the United States, but keeping intact male camelids together frequently results in episodes of intermale aggression to assert territorial and social dominance. Aggressive behaviors include charging other males and forcing body contact, screeching, spitting, mounting, and biting [1]. If these behaviors are frequent, methods implemented by the owner to reduce aggression are necessary. Separating males from a herd can result in further behavioral problems because camelids are a highly social species [2]. Moving males around amongst intermale herds is not ideal either because hierarchal status must be reestablished with each change to the herd or reestablishing hierarchy results in male combat [1]. Castration is a recommended procedure utilized to reduce aggression [3, 4] and is frequently implemented to decrease intermale behavior in many species [2]. Surgical castration is expensive (several hundred dollars per animal) and irreversible. This may not be an ideal solution for owners that do not want the financial burden, want to preserve breeding stock, or want to avoid the risks of
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