Duration of spermatogenesis and daily sperm production in the jaguar (Panthera onca) G.M.J. Costa a , H. Chiarini-Garcia b , R.G. Morato c , R.L.L.S. Alvarenga a , L.R. Franc ¸a a, * a Laboratory of Cellular Biology, Department of Morphology, Institute of Biological Sciences, Federal University of Minas Gerais, 31270-901 Belo Horizonte, MG, Brazil b Laboratory of Structural Biology and Reproduction, Department of Morphology, Institute of Biological Sciences, Federal University of Minas Gerais, 31270-901 Belo Horizonte, MG, Brazil c Departament of Animal Reproduction, Faculty of Veterinary Medicine and Zootechny, Sa ˜o Paulo University, Sa ˜o Paulo, SP, Brazil Received 15 January 2008; received in revised form 13 May 2008; accepted 11 June 2008 Abstract The jaguar, like most wild felids, is an endangered species. Since there are few data regarding reproductive biology for this species, our main goal was to investigate basic aspects of the testis and spermatogenesis. Four adult male jaguars were utilized; to determine the duration of spermatogenesis, two animals received an intratesticular injection of H 3 -thymidine. Mean (SEM) testis weight and the gonadosomatic index were 17.7  2.2 g and 0.05  0.01%, respectively, whereas the seminiferous tubules and the Leydig cells volume density were 74.7  3.8 and 16.7  1.6%. Eight stages of spermatogenesis were characterized, according to the tubular morphology system and acrosome development. Each spermatogenic cycle and the entire spermatogenic process (based on 4.5 cycles) lasted approximately 12.8  0.01 and 57.7  0.07 d. The number of Sertoli and Leydig cells per gram of testis was 29  4  10 6 and 107  12  10 6 . Based on the number of round spermatids per pachytene spermatocyte (2.8  0.3:1; meiotic index); significant cell loss (30%) occurred during the two meiotic divisions. There were approximately eight spermatids for each Sertoli cell (Sertoli cell efficiency), whereas the daily sperm production per gram of testis was 16.9  1.2  10 6 . We expect that in the near future, the knowledge obtained in the present investigation will facilitate, utilizing germ cell transplantation, preservation of the germinal epithelium and the ability to generate sperm from jaguars in testes of domestic cats. # 2008 Elsevier Inc. All rights reserved. Keywords: Testis; Morphometry; Spermatogenic efficiency; Spermatogenic cycle length; Jaguar 1. Introduction Modern felid species descended from relatively recent (<11  10 6 years ago) divergence and speciation events that produced successful predatory carnivores worldwide [1]. Similar to most wild felids, the jaguar (Panthera onca), the largest felid in the American Continent, is endangered (http://www.iucnredlist.org/), currently threatened by habitat loss, fragmentation, and human persecution [2]. To worsen this situation, the knowledge of male reproductive function in the jaguar is very limited [3,4]. Spermatogenesis is a cyclic, complex and highly organized process in which diploid spermatogonia differentiate into mature haploid spermatozoa. This process is composed of cellular associations called stages, which may be classified according to the www.theriojournal.com Available online at www.sciencedirect.com Theriogenology 70 (2008) 1136–1146 * Corresponding author. Tel.: +55 31 34092816; fax: +55 31 34092780. E-mail address: lrfranca@icb.ufmg.br (L.R. Franc ¸a). 0093-691X/$ – see front matter # 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.theriogenology.2008.06.035