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 fol licular 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 gestati on, 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 r efed) but they were slaughtered 38 h before the estimated time of oest rus. The largest 15 follicles per sow were aspirated and follicular fl uid recovered for analysis in vitro. Although plasma oestradiol concen tration 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 scor es in vitro were not different between treatments, although more (P < 0.03) oocytes from refed sows had matured to metaphase II than those f rom restricted sows. Similarly, although cumulus expansion of oocyte-c umulus complexes from prepubertal gilts oocytes incubated with follicu lar fluid obtained from restricted (n = 1227) or refed (n = 1147) sows was not different (P > 0.05), the rate of oocyte nuclear maturation w as greater (P < 0.012) after incubation with follicular fluid from ref ed than with that from restricted sows. Differences in the maturation of the follicle and oocyte in the period before the LH surge may there fore contribute to the treatment effects on embryo survival.