Asynchronous breeding in red brocket deer (Mazama americana): seasonal changes in male reproductive characteristics, seminal parameters, androgen levels, and antler cycle

The red brocket deer is the largest species in the genus Mazama and one of the most abundant and widely distributed cervid in the Neotropics. Yet it has been classified as data deficient by the IUCN, and the limited knowledge on its reproductive biology indicates that red brocket bucks do not possess an annual antler cycle and are capable of breeding during antler casting and growth. Here, in parallel to antler cycle, we investigated seasonal changes in morphometric (body weight, neck and chest girth, and testicular volume), endocrine [plasma testosterone and fecal androgen metabolites (FAM) levels] and seminal (total sperm count and sperm motility index) parameters from captive adult red brocket bucks collected on a quarterly basis over a 1-year period. Two out of six males kept hard antlers year-round, three cast antlers from winter to spring, and one carried velvet antlers for longer than 6 months. No clear seasonal patterns of variation in gross morphometry, seminal traits, and hormonal levels were found, and mean values of all collected parameters did not show differences among seasons. Body weight was positively correlated with most morphometric measurements and seminal parameters, while chest girth was positively correlated with neck girth, testicular volume, and total sperm count. Neither androgen levels (both plasma testosterone and FAM) nor hard antler phase correlated with seminal characteristics. Our findings support that red brocket bucks not only exhibit aseasonal and asynchronous antler cycles, but also maintain their secondary sexual characteristics and semen quality unchanged over the year. This apparent lack of photoperiodic stimuli for controlling reproduction along with an absence of relationship between seminal parameters and antler status might make red brockets unique in terms of reproductive biology among deer species.