The goal of this experiment was to provide information about the pattern of progesterone secretion (P4) and on the oestrus cycle characteristics in hair and wool ewe lambs, from April to November, in São Paulo State. Blood samples from jugular vein were collected from 12 ewe lambs Santa Inês (SI), Romney Marsh (RM) and Suffolk (SU) breeds, and the concentrations were determined by radioimmunoassay method, using commercial kits. Oestrus was detected by using vasectomized rams (fitted with raddle crayons + comestible oil on pectoral area) in 31 ewe lambs (10 SI, 11 RM and 10 SU). The oestrus was determined by confronting the observation of marked females by vasectomized rams and values of plasma progesterone concentrations lower than 1 ng/mL. The results showed that the majority of oestrus cycles were of normal lenght (14 ¾ 19 days) for all breeds. The normal cycles lenght for the SU ewe lambs was shorter than SI and RM, which did not differ from each other. There was no difference for short (<14 days) and long (20 - 26 days) oestrus cycles duration between the breeds. The pattern of P4 secretion showed the presence of multiples oestrus cycles (27 ¾ 57 days) leading to the incidence of silent ovulations. SI ewe lambs were in cyclic activity, showing values from 0.08 to 7.36 ng/mL, while RM and SU breeds were in activity only from April to July with values from 0.13 to 7.05 ng/mL and from 0.15 to 7.30 ng/mL, respectively. From August to November, these two breeds were in anoestrus. It was concluded that, in São Paulo State, SI breed does not have a stationary on reproductive cycle, as RM and SU breeds.
breeds; oestrus cycle; ovine; progesterone
