In the Mediterranean environment and subtropical microclimate of the south-east Iberian Peninsula (37° 59' N), testicle size and sexual behaviour of male goats were studied and the influence of season (day length, air temperature and relative humidity) on these factors examined.
Nine, 13-month-old Murciano-Granadina male goats weighing 47 to 53 kg were used. The experiment began during the month of January and extended for a complete year. Every 2 weeks, anterior-posterior maximum testis diameter was measured. They were tested twice a week for levels of sexual behaviour using ovariectomized goats and libido was evaluated as reaction time to mating.
The annual mean testis diameter was 5·06 (s.e. 0·02) cm, varying significantly with season of the year. The lowest values were measured during winter 4·89 (s.e. 0·03) cm. These increased (P <0·01) in spring (5·16 (s.e. 0·01) cm) and summer (5·19 (s.e. 0·02) cm), but decreased again (P <0·01) in the autumn (5·04 (s.e. 0·02) cm). The annual mean reaction time was 197 (s.e. 12) s, but was longest (P <0·01) in spring (318 (s.e. 30) s), and shortest during summer (144 (s.e. 16) s) and autumn (132 (s.e. 17) s). The testicle diameter measurement was correlated with day length (r = 0·41; P <0·01) and air temperature (r = 0·45; P<0·01), while the reaction time showed no relationship with climatic measurements.
It was concluded that day length is not the only factor responsible for seasonal variation in testis size of Murciano-Granadina male goats and that, in their natural habitat, libido is unlikely to be a limiting factor in the breeding programme.