A lower incidence of return to estrus has been reported in herds where sows were inseminated only once per estrus (elbers et al .1995 ) lower parities,farrowing during the spring and summer, lower lactational feed intake and shorter lactation lengths are factors associated with an increase in the occurrence of a return to estrus (Koketsu and Dial,1997 ;koketsu al ;1997 )The presence of cysts was associated with a compromised reproductive performance expressed by lower farrowing rate ( 52 vs 90 ) higher return to estrus (34 vs 7.7)and higher failure to farrow (10.6 vs 0.6) in 47 females with cysts compared to 1943 females without cysts (Castagna et al.2004)