Two experiments were carried out to evaluate the effect of previous incubation and cooling rate on the viability of swine cooled semen. Semen doses of 100ml, containing three billion spermatozoa, were stored at 17ºC or 5ºC. Percentages of motility (MOT), normal acrosomes (ACN), and intact membranes (MI) were evaluated. A number of 5 and 6 ejaculates were collected from 6 and 4 boars in experiments I and II, respectively. In experiment I, three treatments were compared: storage at 17ºC (T1); storage at 5ºC with 24h incubation at 17ºC (T2), and at 5ºC, after a slow (about 15h to reach 5ºC) temperature decrease (T3). T1 presented better results (P<0.05) for MOT and MI as compared to T2 and T3. No difference (P>0.05) was found in MOT and MI between T2 and T3 and in ACN (P>0.05) among the three treatments. In experiment II, 4 treatments were evaluated: storage at 17ºC (T1); at 5°C with 24h incubation at 17ºC (T2); at 17ºC with previous 8h incubation at 22ºC (T3), and storage at 5ºC (T4) with two incubation temperatures and periods (at 22ºC for 8h and at 17ºC for 16h). No difference (P>0.05) was verified in MOT, ACN and MI between T1 and T3 and also between T2 and T4. Storage at 17ºC (T1 and T3) presented better MOT and MI (P<0.05) as compared to storage at 5ºC (T2 and T4), from 72h onwards. Previous incubation or slow temperature decrease as well as incubation for 24h at 17ºC or for 8h at 22ºC plus 16h at 17ºC do not affect the viability of semen stored at 5ºC. Cooling to 5ºC still needs to be optimized so that viability be similar to that observed at 17ºC.
incubation; cooling; semen; swine
