Nursing during the first 48 H of life is important for expression of proteins involved in neonatal porcine cervical development at postnatal day 14

The first two weeks of neonatal life in pigs is a critical periodfor reproductive tract programming. Data for the uterus indicatethat disruption of gene expression between birth (postnatalday = PND 0) and PND 14 changes the developmental trajectoryof these tissues. Colostrum, or first milk, may play a rolein maternal programming of neonatal development. The lactocrinehypothesis was proposed as a mechanism whereby bioactive milk-bornefactors delivered to nursing offspring affect tissue development.Compared to nursing animals, expression of markers of cervicaldevelopment in neonatal gilts fed a hormone-free milk replacerfrom birth is altered by PND 2. The extent to which this 48h window of sensitivity to milk-borne factors influences subsequentcervical development is unknown. In addition, whether effectsof the absence of nursing on the cervical phenotype at PND 2can be reversed by returning gilts to nursing has not been investigated.Objectives were to determine effects of age at first nursing(birth or PND 2) and both duration and period of nursing onexpression of molecular markers of cervical growth, remodelingand apoptosis at PND 14. Targeted proteins included estrogenreceptor-alpha (ESR1) and vascular endothelial growth factor(VEGFA), both mediators of porcine cervical growth, matrix metalloproteinase2 (MMP2), involved in tissue remodeling, and the anti-apoptoticmarker BCL2. Gilts (n = 5-11/group) were assigned randomly toone of four treatment groups at birth, in which they were: 1)allowed to nurse ad libitum; 2) pan-fed a hormone-free milkreplacer ad libitum; 3) nursed for 48 h from birth and switchedto replacer; or 4) fed replacer for the first 48 h of life andswitched to nursing. Cervices were collected on PND 14. Proteinexpression was evaluated by immunoblotting, using actin as aloading control, and quantified by densitometry. Expressionof cervical ESR1 and BCL2 proteins, undetectable at PND 0, wasinduced in PND 14 gilts nursed from birth, but remained undetectablein gilts fed replacer during the first 48 h of life. VEGFA protein,undetectable at PND 0, was detectable on PND 14 in all groups,but was markedly reduced (p > 0.01) in PND 14 gilts fed replacerfrom birth. Latent MMP2 was detectable at similar levels atbirth and on PND 14 in nursed and replacer-fed gilts. ActiveMMP2, undetectable at PND 0, was induced in both nursing andreplacer-fed gilts by PND 14. There were no differences in cervicalESR1, VEGFA or BCL2 protein levels in gilts allowed to nursecontinuously for two weeks or for only 48 h from birth. Datasupport the lactocrine hypothesis for maternal programming ofneonatal development, indicating that milk-borne factors arerequired to support protein expression patterns important forcervical development in the neonatal gilt. Results indicatethat the first 48 h of neonatal life constitutes a potentiallycritical period for lactocrine signaling in porcine cervicaltissues. This idea is supported by the fact that effects ofdisruption of lactocrine signaling on cervical development betweenbirth and PND 2 persisted to PND 14 even when replacer-fed giltsreturned to nursing after PND 2. Thus, in the absence of lactocrinesignaling from birth, altered expression patterns for morphoregulatoryproteins, as observed here, could affect the cervical developmentaltrajectory with long-term consequences for reproductive performanceand health.