Endocrine Abstracts

It is well established that the reduced neonatal mortality in Meishan, compared to commercial piglets, is due to resistance to hypothermia and hypoglycaemia. Underlying factors responsible for the differences in survival may include the disparity in plasma tri-iodothyronine (T₃) concentrations and UCP expression (Mostyn et al (2004) Journal of Endocrinology, in press). ZD7114 (ZD), a synthetic beta3-adrenoceptor agonist, has been shown to improve thermogenesis in lambs but it is unknown whether a similar effect would occur in pigs. This study investigated the influence of hormonal manipulation and temperature on AT UCP3 expression in newborn piglets.

On the first day of postnatal age, piglets from 12 Meishan and 12 Commercial litters were ranked according to weight and the 3 median piglets were randomly assigned to control (C) (1ml/kg water), ZD (10mg/kg) or T₃ (370ng/kg) treatment given as a bolus oral dose in 3ml synthetic sow milk. Piglets were then maintained at a warm (24degC) or cool (14degC) environmental temperature for 180 minutes then humanely euthanased to obtain AT. UCP3 RNA was then quantified by RT-PCR as described previously (Mostyn et al; 2004, Journal of Endocrinology, in press). GLM analysis was performed and results are presented as means ± standard errors.

AT UCP3 expression was unaffected by temperature, irrespective of treatment. T₃ or ZD treatment significantly increased UCP3 expression in both breeds, although this was most apparent in Meishan piglets treated with ZD (warm ZD, 416.6±142; warm C, 76±20.8; cool ZD 331.9±142; cool C 70.1±17.7 (p<0.05)).

In conclusion, ZD and T₃ treatment up-regulated AT UCP3 expression in piglets. It was also demonstrated that Meishan piglets are more sensitive to ZD treatment than leaner commercial breeds. The lower mortality rates in Meishan piglets may be attributed to a greater abundance of beta3-adrenoreceptors in adipose tissue. This would be revealed with further research.