Influence of genotype on the endocrine and metabolic control of uncoupling protein (UCP)-2 during the first week of life in neonatal piglets
A Mostyn1, JC Litten1, KS Perkins1, ME Symonds2 & L Clarke1
It is well established that neonatal mortality is greater in the leaner commercial (C) porcine genotypes compared to the ancient Meishan (M) breed, which has a higher percentage of body fat. Piglets do not express UCP1, responsible for heat production in neonatal mammals, although they do express UCP2. The aim of this study was to investigate the endocrine and metabolic control of UCP2 expression between the C and M genotypes.
Piglets from 15 C and 15 M litters were ranked according to birth weight and the 3 median piglets were randomly sampled on days 0, 4 and 7 of neonatal life. Piglets were weighed and colonic temperature measured on these days and a venous blood sample taken. Subcutaneous adipose tissue (scAT) was also sampled for laboratory analysis after humane euthanasia. Plasma non-esterified fatty acids (NEFA) and Triiodothyronine (T3) concentrations were analysed using enzymatic and radioimmunoassay respectively. Total RNA was extracted from scAT and UCP2 mRNA examined by RT-PCR, using porcine specific primers. Results, in arbitrary units, are a ratio of an 18S rRNA internal control.
M piglets weighed less the C group and were colder throughout the study. UCP2 expression in scAT was higher in the C group on days 0, 4 and 7. UCP2 was significantly correlated with T3 on day 0 (R2=0.6, P<0.05) and NEFA on day 4 (R2=0.4, P<0.01) in the C group and with NEFA on day 7 (R2=0.4, P<0.01) in the M group.
In conclusion, differential UCP2 expression was observed between the two pig genotypes with postnatal age. Although UCP2 was not directly related to temperature, there was a significant correlation with T3 and NEFA, suggesting a role in thermogenesis in neonatal piglets.