CIRCANNUAL INTERRELATIONSHIPS AMONG REPRODUCTIVE HORMONES, GROSS MORPHOMETRY, BEHAVIOR, EJACULATE CHARACTERISTICS AND TESTICULAR HISTOLOGY IN ELDS DEER STAGS (CERVUS-ELDI-THAMIN)

Blood samples, morphometric measurements and behavioural data were col lected weekly for 52 weeks from six adult Eld's deer stags exposed to natural fluctuations in photoperiod (38-degrees-N latitude). Mean (+/- SEM) serum LH concentrations reached peak values in the autumn (Octob er), three months before FSH and testosterone concentrations reached p eak values in early winter (January). Prolactin concentrations were in versely related (r = -0.733, P < 0.001) to LH and directly related to daylength, and maximal concentrations were observed during mid-summer (July) and minimal concentrations during early winter (January). The t emporal pattern of circulating inhibin was positively correlated with FSH (r = 0.88, P < 0.001), but lagged behind the seasonal FSH increase by 1-3 weeks. Antler length, body weight and chest girth were maximal during pre-rut (December-January). Maximal scrotal circumference and combined testes volume were observed in mid-winter (February), whereas peak neck girth and behavioural aggression occurred 1-3 months later (March-May). On the basis of quarterly electroejaculation results, mot ile spermatozoa were produced in all seasons. However, the greatest nu mber of motile spermatozoa per ejaculate was observed during the winte r and spring, whereas the highest incidence of sperm pleiomorphisms (> 80%) was detected in the autumn. Histological assessments of the regr essed testis (July) revealed fewer germ cells undergoing spermatogenes is and an increased incidence of degenerating and abnormal cell types. In summary, Eld's deer exhibit a circannual hypothalamic-pituitary-go nadal cycle with onset of pituitary activation occurring during the au tumn and winter, whereas gonadal activity peaks during the winter and spring as daylengths are increasing. Marked circannual variations in c irculating prolactin suggest that Eld's deer may use photoperiodic cue s to modulate seasonal fertility; however, the existence of an endogen ous seasonal rhythm operating independently of photoperiod cannot be e xcluded.