Similar results for primiparous and multiparous sows held in high temperatures
were given by Prunier et al. (1997), where at temperatures of 27–30°C litter sizes
were similar. Another study conducted by Gourdine et al. (2006) revealed the negative
effect of climate only on primiparous sows and also a greater significance of
season on insemination. The low number of piglets born alive after May insemination
for sows in parity group 5–11 (9.90) could be explained by the highest level of
prolactin blocking ovulation recorded in this month, as noted by Bassett et al. (2001).
It can be deduced that older females are especially susceptible to the activity of this
hormone.
to crossbred sows.