Use of Plasma Orosomucoid in Newborn Piglets to Predict Preweaning Growth Performance and its Potential Mechanism of Action

Abstract Text: Orosomucoid (ORM) is the most prevalent serum protein in the newborn pig.  The present study was designed to determine if plasma ORM at birth can be used to predict the relative performance of piglets within a litter between birth and weaning using a highly sensitive ELISA specific for pig ORM.  Secondly, this study looked at the potential mechanism of action of ORM on growth by examining the effects of ORM on protein synthesis in vitro.  Plasma was obtained from 19 litters (202 piglets) at the US Meat Animal Research Center.  Parity ranged from 1 to 4 (2.4 ± 0.6) with an average litter size of 10.6 ± 0.4 pigs.  Samples were analyzed using a pig ORM ELISA developed by USDA-ARS Beltsville.  Plasma ORM in newborn piglets was negatively correlated with growth rate between birth and weaning at 21 days of age (linear regression correlation coefficient [CC] = - 0.225, p < 0.003).  This correlation was improved by expressing plasma ORM relative to total plasma protein (CC = - 0.370, P < 0.0001).  When ORM was calculated on a per kg birth weight basis, the CC further improved (-0.462, P < 0.0001).  How elevated concentrations of plasma ORM at birth are related to poor postnatal growth has not been identified.  Therefore, in vitro experiments were performed to determine if ORM can interfere with protein synthesis using the skeletal muscle C₂C₁₂ cell line.  C₂C₁₂ myotubes were treated with serum free Dulbecco’s modified Eagle’s medium, 0.5% BSA, and 0, 0.1, 1.0 or 10.0 µg/mL mouse ORM in the initial experiment.  Treatments were added to cultures for 1 hour, then supplemented with 0.5 µCi ³H-tyrosine/mL medium for an additional 2 hours for a total exposure time to ORM for 3 hours, followed by washes and protein extraction.  ORM had no effect on protein synthesis as measured by ³H-tyrosine incorporation (p > 0.05; n = 4 trials).  Treatment with 20 ng IGF1/mL medium increased ³H-tyrosine incorporation by 53% (P < 0.01, n = 3 trials); whereas the addition of ORM reduced IGF1 induced ³H-tyrosine incorporation by 40% (P < 0.01, n = 3 trials).  These data indicate that ORM can indirectly reduce ³H-tyrosine incorporation into C₂C₁₂ myotube proteins by altering IGF1 efficacy, suggesting ORM interferes with the growth promoting effects of IGF1 and may contribute to the observed negative correlation between plasma ORM at birth and preweaning growth rates in swine.

 Keywords: orosomucoid, biomarker, growth, neonate, alpha 1-acid glycoprotein