Photoperiodic Control of the Concentration of Luteinizing Hormone, Prolactin and Testosterone in the Male Emu (Dromaius novaehollandiae), a Bird that Breeds on Short Days D. Blache,* R. T. Talbot,² M. A. Blackberry,* K. M. Williams,* G. B. Martin* and P. J. Sharp² *Faculty of Agriculture (Animal Science), The University of Western Australia, Nedlands, Western Australia, Australia. ²Division of Integrative Biology, Roslin Institute, Roslin, Midlothian, UK. Key words: emu, LH, photoperiodism, photorefractoriness, prolactin, ratite, seasonal breeding, testosterone. Abstract The objective of this study was to establish, for a short-day breeding bird, the male emu, whether the breeding season is principally controlled by changes in photoperiod, and to investigate the endocrine mechanisms involved. Two groups of adult males were subjected to three alternating periods of 150±185 days of 14 h light/day (LD) and 10 h light/day (SD) terminating in a 360-day period of LD or SD. Transfer from LD to SD led to increases in plasma concentrations of luteinizing hormone (LH) and testosterone, after 82t8 and 73t3 (SEM) days, and an increase in prolactin concentrations after 115t12 days. Concentrations of LH and testosterone began to decrease before transfer back to LD, at a time when prolactin concentrations were approaching peak values. Transfer from LD to 360 days of SD resulted in increases in LH and testosterone concentrations, and these terminated after an increase in prolactin concentrations. After transfer from SD to 360 days of LD, plasma concentrations of LH and testosterone began to increase, after delays of 222t24 and 225t13 days, and were high at the end of the study, while prolactin values remained depressed throughout. These observations clearly show that seasonal breeding in the emu is directly controlled by changes in photoperiod. The dynamics of the hormonal responses to change of photoperiod suggest that, despite being short-day breeders, the photoregulation of breeding in emus involves mechanisms that are currently accepted for birds, rather than mechanisms that have been proposed for short-day breeding mammals. The initiation of breeding in emus is due to dissipation of photorefractoriness by short days which leads to an increase in the secretion of gonadotrophins to levels that are suf®cient to support full reproductive condition. The termination of breeding, while days are still short, is due to the antigonadotrophic action of prolactin which, unusually for birds, increases while the days are still short. In conclusion, breeding activity in male emus is strongly controlled by photoperiod. Emus are short-day breeders, but the central mechanisms that regulate the secretion of reproductive hormones seem to be similar to those previously proposed for long-day breeding birds. The pattern of prolactin secretion in emus suggests an important role for this hormone in the termination of the breeding cycle. Most birds living at nonequatorial latitudes are long-day breeders (1, 2) but some, such as the emu in South-Western Australia, breed during autumn and winter, both in the wild and in captivity (3±5). As in other avian species, the timing of breeding in the emu may be in¯uenced by a range of environ- mental factors, including photoperiod (1, 2, 6, 7), food availability, rainfall and social and behavioural signals (1). Rainfall, in particular, appears to stimulate early breeding in the emu (8, 9). In male birds that breed on long days, the onset of breeding is associated with photoperiod-induced increases in the plasma concentrations of luteinizing hormone (LH) and testosterone, followed by an increase in prolactin concentra- tions. Many birds terminate seasonal breeding by the develop- ment of reproductive photorefractoriness, a condition that is characterized by low plasma concentrations of LH, testo- sterone and prolactin (10±13). A similar relationship between the onset and termination of breeding and changes in the concentrations of these three hormones is observed in male Correspondence to: Dr Dominique Blache, Faculty of Agriculture (Animal Science), The University of Western Australia, Nedlands, WA 6907, Australia (e-mail: dblache@agric.uwa.edu.au). Journal of Neuroendocrinology, 2001, Vol. 13, 998±1006 # 2001 Blackwell Science Ltd