A lower incidence of return to estrus has been reported in
herds where sows were inseminated twice or more per
estrus than in herds in which sows were inseminated only
once per estrus (Elbers et al., 1995). Lower parities,
farrowings 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 et 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 (34.0%vs.7.7%) and
higher failure to farrow (10.6% vs. 0.6%) in 47 females with
cysts compared to 1943 females without cysts (Castagnaet al., 2004).