ESTROGEN ASSOCIATED CHANGES IN UTERINE BLOOD-FLOW AND MATERNAL RECOGNITION OF PREGNANCY IN CHINESE (MEISHAN) PIGS

Our laboratory has recently demonstrated a reduced embryonic growth ra te and estradiol-17beta (E2beta) content of preimplantation Meishan em bryos compared with embryos of European breeds. Estrogen secretion by the preimplantation conceptus has been linked to both the transient in crease in uterine blood flow (UBF), and maternal recognition of pregna ncy (MRP) on Days 11-13 of gestation in European swine breeds. The obj ective of these experiments was to evaluate the temporal association b etween estrogen secretion by the preimplantation conceptus, increases in UBF and the onset of MRP in Meishan pigs. In Experiment 1, multipar ous Meishan sows (N = 3) were observed for estrus once daily, and hand -mated at first observed estrus (Day 0) and 24 h later with a Meishan boar. On Day 2 postmating, sows were bilaterally instrumented with blo od flow transducers and uterine venous catheters. UBF (ml min-1) was m onitored and blood samples collected once daily from Days 6 to 30 post mating. UBF increased on Day 11 (P = 0.06) to peak on Day 13, then dec reased on Days 14-17, before increasing progressively thereafter, coin cident with increasing uterine E2beta secretion. In Experiment 2, seco nd cycle Meishan (N = 20) and Yorkshire (N = 18) gilts were hand-mated at first observed estrus (Day 0), and 24 h later, to boars of their o wn breed. Embryos were flushed from the gilts on Day 9, 11, 13 or 15 p ostmating. Gilts were again observed for estrus to determine treatment estrous cycle length (ECL). Treatment ECL was similar (P > 0.1) to pr esurgical ECL when embryos were collected from either Meishan or Yorks hire gilts on Days 9 and 11. ECL was extended in both breeds (P < 0.05 ) when embryos were recovered on Days 13 and 15.