Seasonality of plasma testosterone in males of four Mediterranean goat breeds and in three different climatic conditions

Abstract The aims of the present work were to evaluate if a seasonality of plasma testosterone concentrations exists in Mediterranean male goats and it may be affected by climatic conditions. Testosterone concentrations were determined throughout 1 year in blood samples collected weekly from 24 males of 4 Mediterranean goat breeds (Ionica, Garganica, Maltese and Red Syrian), fed a constant diet, maintained without interactions with does and reared in 3 farms with different climates, in Italy. Plasma testosterone concentrations were affected by season (P < 0.0001), being higher during summer (8.33 _ 0.35 ng/mL) than during autumn (6.81 _ 0.26 ng/mL), which were in turn higher than in winter (1.55 _ 0.08 ng/mL) and spring (2.04 _ 0.15 ng/mL). An effect of breed was recorded (P < 0.001), Ionica bucks having the highest plasma testosterone means, Red Syrian and Maltese the lowest. The onset of the reproductive season was similar among the breeds. Ionica bucks had a later offset than Red Syrian and Maltese and a longer reproductive season than Maltese bucks (P < 0.05). No effect of farm nor interaction breed _ farm was recorded. Single sporadic peaks of plasma testosterone were recorded in many bucks, outside the main reproductive season, especially during spring. In conclusion the bucks of all the four breeds displayed a clear seasonality of plasma testosterone, with very low levels from January to May and high levels from July to November; hormone levels and pattern of seasonality were affected by breed and not by climate. # 2006 Elsevier Inc. All rights reserved. Keywords: Bucks; Testosterone; Reproduction; Season; Climate