Follicle size at ovulation may affect fertility in sows

The follicle size at ovulation is known to be between 6 and 9 mm in the
pig. Little is known if this size affects the subsequent fertility. In the
present study, the connection between the size of the follicles at
ovulation and the size of the live born litter is investigated. Sows
(n = 93) from a sow pool system, that had farrowed at least once and
had a WOI of 4–6 days were included. Starting at day 3 after weaning,
sows were checked for standing oestrus in the presence of a boar twice
a day. When in heat, ovaries were ultrasounded one-sided transabdominally
twice a day until ovulation. The three largest follicles were
repeatedly measured to assess timing and size at ovulation. For the
analysis, a multiple linear regression model was used. Additionally to
the follicle size, the parity, breed, number of inseminations, the boar
and whether or not the inseminator got informed about the time of
ovulation, were considered as explanatory variables. Out of the
variables, only parity 2.9; p ± (4.8 < 1.8; p ± 0.05) and follicle size
at ovulation (7.3 < 4.3). Follicles±0.05) influenced the live born litter
size (11.1 ovulating at the size of 7–8 mm resulted in larger live born
litters than follicles ovulating at <7 or >8 mm. These results indicate
that there is an optimal size of follicles at ovulation. Ovulation at too
small or too large follicular size may be linked to inadequate hormonal
control of ovulation. This mechanism is likely to include LH and
oxytocin secretion. Work is underway to explore this mechanism.