Temporal and seasonal relationships between LH, testosterone and antlers in fawn and adult male roe deer

Abstract

Abstract. Plasma LH and testosterone patterns, testis and antler growth and rutting period were determined in the roe deer from birth to 4 years of age. In adults, a typical annual cycle was observed for these endocrine growth and behaviour events. The greatest testosterone levels (9.65 ng/ml) and testis size (13.13 cm3) were recorded for an average period of one month, from July 15th to August 15th, and coincided with the rutting period. At this time antler size was maximal (from 12.70 to 21.35 cm according to age). Plasma testosterone levels and testis size decreased rapidly from September until December (0.23 ng/ml and 3.48 cm3, respectively) and casting occurred at the same time as the decrease of testosterone. It was concluded that testosterone release is an important factor which is correlated with testis growth, antler maintenance and rutting behaviour. Plasma LH levels showed large fluctuations throughout the year and an annual cycle was demonstrated. The lowest plasma LH concentrations were recorded in December (1.36 ng/ml) while higher values were recorded in February (3.25 ng/ml). This suggests that an increase of pituitary gonadotrophic activity appears in spring and is responsible for the testicular reactivation. In the roe deer as in other seasonally breeding species it may be inferred that gonadotrophic activity is controlled by daylength. The present findings show that sexual activity is initiated by increasing daylength and that the roe buck is the only cervidae whose breeding period is early summer. In fawns, a low plasma testosterone level (1.27 ng/ml), a small testis size (2.96 cm3) and antler growth ('buttons') were observed a few months after birth in autumn and high plasma LH levels (4.08 ng/ml) were recorded before this, as early as the first month of age. It is suggested that interrelationships between LH, testosterone, testis and antler growth begin to appear at this time and that the precocious LH release induces the first pubertal testicular activity. This first increase of gonadotrophic activity which appears in summer can not be related to the photoperiod as in adults and would be under central endogenous control for the onset of the pubertal maturation process. From this pubertal state (3 months of age) to the following testicular initiation where potential sexual maturity is probably reached (7-9 months of age), complex temporal interrelationships occur between daylength, gonadotrophic and testicular factors.