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Ashley F George, Kathleen M Rahman, Dori J Miller, Anne A Wiley, Meredith E Camp, Frank F Bartol, and Carol A Bagnell

Nursing ensures lactocrine delivery of maternally derived, milk-borne bioactive factors to offspring, which affects postnatal development of female reproductive tract tissues. Disruption of lactocrine communication for two days from birth (postnatal day (PND) 0) by feeding milk replacer in lieu of nursing or consumption of colostrum alters porcine uterine gene expression globally by PND 2 and inhibits uterine gland genesis by PND 14. Here, objectives were to determine effects of: (1) nursing or milk replacer feeding from birth; (2) a single dose of colostrum or milk replacer and method of feeding and (3) a single feeding of colostrum or milk replacer, with or without oral supplementation of IGF1, administered at birth on aspects of porcine uterine development at 12-h postnatally. Results indicate nursing for 12 h from birth supports rapid establishment of a uterine developmental program, illustrated by patterns of endometrial cell proliferation, expression of genes associated with uterine wall development and entry into mitosis and establishment of a uterine MMP9/TIMP1 system. A single feeding of colostrum at birth increased endometrial cell proliferation at 12 h, regardless of method of feeding. Oral supplementation of IGF1 was sufficient to support endometrial cell proliferation at 12 h in replacer-fed gilts, and supplementation of colostrum with IGF1 further increased endometrial cell proliferation. Results indicate that lactocrine regulation of postnatal uterine development is initiated with the first ingestion of colostrum. Further, results suggest IGF1 may be lactocrine-active and support a 12-h bioassay, which can be used to identify uterotrophic lactocrine activity.

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Joseph C Chen, Amy-Lynn Frankshun, Anne A Wiley, Dori J Miller, Kristene A Welch, Teh-Yuan Ho, Frank F Bartol, and Carol A Bagnell

Lactocrine communication of milk-borne bioactive factors (MbFs) from mother to offspring through nursing can affect neonatal development with lasting consequences. Relaxin (RLX), a lactocrine-active peptide found in porcine colostrum, stimulates estrogen receptor-α (ESR1) expression required for uterine development shortly after birth (postnatal day=PND 0). Whether other MbFs or cooperative lactocrine mechanisms affect the neonatal uterine developmental program is unknown. To determine the effects of age, nursing, and exogenous RLX on gene expression associated with uterine development, gilts (n=4–5/group) were assigned to nurse ad libitum or to receive milk replacer, with or without exogenous RLX (20 μg/kg BW i.m./6 h for 48 h), from birth to PND 2 when uteri were collected. Body weight and uterine weight increased (P<0.05) similarly from birth to PND 2 in all gilts. However, colostrum consumption was required for normal uterine ESR1, vascular endothelial growth factor (VEGFA), matrix metalloproteinase 9 (MMP9), and RLX receptor (RXFP1) protein and/or transcript expression on PND 2. Uterine ESR1, VEGFA, and MMP9 protein levels were below (P<0.01) the assay sensitivity in replacer-fed gilts. Supplemental RLX increased (P<0.05) uterine ESR1 protein and mRNA in nursed gilts, as well as VEGFA protein in nursed and VEGFA mRNA in both nursed and replacer-fed gilts. RLX treatment did not affect uterine MMP9 mRNA levels. When compared with replacer-fed gilts on PND 2, uterine RXFP1 mRNA was reduced (P<0.05) in nursed gilts and in RLX-supplemented replacer-fed gilts. These results constitute the first evidence that establishment of the neonatal porcine uterine developmental program requires maternal lactocrine support.