Impact of different patterns of feed intake during lactation in the primiparous sow on follicular development and oocyte maturation.

The potential contribution of nutritionally induced differences in follicular and oocyte maturity to embryo survival was addressed in pigs. When primiparous, lactating sows are fed to appetite from farrowing to day 21 of lactation and then with feed intake restricted to 50% from day 22 to 28 (restricted), embryo survival is 64% at day 28 of gestation, compared with 85% in sows fed to 50% from farrowing to day 21 and then fed to appetite from day 22 to 28 (refed). In the present study, 32 sows were equally assigned to these two treatments (restricted or refed) but they were slaughtered 38 h before the estimated time of oestrus. The largest 15 follicles per sow were aspirated and follicular fluid recovered for analysis in vitro. Although plasma oestradiol concentration before slaughter and follicular fluid oestradiol concentration at slaughter were not different (P > 0.05), refed sows had more (P < 0.02) large follicles than did restricted sows. Cumulus expansion scores in vitro were not different between treatments, although more (P < 0.03) oocytes from refed sows had matured to metaphase II than those from restricted sows. Similarly, although cumulus expansion of oocyte-cumulus complexes from prepubertal gilts oocytes incubated with follicular fluid obtained from restricted (n = 1227) or refed (n = 1147) sows was not different (P > 0.05), the rate of oocyte nuclear maturation was greater (P < 0.012) after incubation with follicular fluid from refed than with that from restricted sows. Differences in the maturation of the follicle and oocyte in the period before the LH surge may therefore contribute to the treatment effects on embryo survival.