duration of lactation endocrine and metabolic state and fertility of primiparous sows the objectives of this study were to determine factors affecting the reproductive performance of primiparous sows early weaned ew n 35 at d 14 or conventionally weaned cw n 35 at d 24 of lactation sow bw and backfat were recorded at farrowing weekly until weaning and at standing heat feed intake was controlled throughout lactation to standardize nutritional effects on subsequent reproductive performance litter size was standardized across treatments within 48 h after farrowing and litter weight was recorded until weaning in subsets of sows blood samples were collected from 10 h before to 10 h after weaning and then every 6 h until ovulation sows were heat checked twice daily and bred at 24h intervals during standing heat using pooled semen ultrasonography every 6 h determined time of ovulation sows were either slaughtered within 24 h after ovulation to assess ovulation rate fertilization rate and embryonic development in vitro or at d 28 of gestation to determine ovulation rate and embryonic survival compared with cw sows ew sows had more backfat at weaning 159 05 vs 147 05 mm p 0001 also cw sows tended to lose more bw and to have lower igfi concentrations indicating poorer body condition duration of lactation did not affect ovulation rate ew 176 07 cw 187 06 fertilization rate ew 960 22 cw 882 47 or embryo survival to d 28 ew 625 45 cw 631 50 there was a marginal effect of duration of lactation on weaningtoestrus interval ew 120 3 cw 112 3 h p 006 and duration of estrus ew 524 23 cw 463 22 h p 008 overall embryonic survival not ovulation rate seems to be the limiting factor for potential litter size in the second parity although fertility in both ew and cw sows studied was compromised endocrine and metabolic data indicate that the mechanisms affecting reproductive performance may differ between the two weaning systems the lh fsh and estradiol data from the ew sows are characteristic of animals with limited follicular development and incomplete recovery of the hypothalamicpituitaryovarian axis consequently the integrity of the uterine environment may be adversely affected and limit embryonic survival in cw sows variability in metabolic state seemed to be the key factor limiting the fertility again adversely affecting embryonic survival