Background and aims: It has been established that the early life nutritional environment affects current and later adiposity, and therefore adult health outcomes and phenotypes (1). Using sheep as a model, we examined the effects of excess energy intake during early postnatal life on the subsequent growth and development of sternal adipose tissue. Specifically we looked at the expression of adipose tissue-related genes including leptin, adiponectin, FABP4, HOXC9, PPARγ, RIP140 and CIDEA. We hypothesised that excess energy intake would increase the amount of sternal fat, and that genes involved in excess adiposity would respond accordingly. Materials and methods: Weight-matched offspring of 13 twin-bearing ewes were separated from their mothers and randomly allocated to one of two different dietary groups from day 3 postpartum until 6 months of age. Each group was balanced by sex. The control group (C, n=13) was fed milk replacer diet for 8 weeks, with green hay added from 14 days of age. The high-carbohydrate high-fat group (HCHF, n=13) was fed a 1:1 mixture of milk replacer and cream together with maize from 14 days of age. At 6 months animals were humanely euthanased and sternal adipose tissue depots dissected. The relative expression of genes of interest was assessed by qPCR. Expression of genes of interest was normalised to the geometric mean expression of two reference genes that had been tested for stability. Gene expression was determined by the comparative CT method after corrections for qPCR efficiency. Values shown are the mean ± SEM in arbitrary units. A two-tailed t-test or Mann-Whitney U-test, as appropriate, was used to compare gene expression between the two groups. Results: At 6 months of age, animals on the HCHF diet were heavier than those on the control diet (C: 36.05 ± 0.79 kg; HCHF: 42.28 ± 2.63 kg; p<0.05) and possessed more sternal fat than controls, both in total (C: 36.5 ± 2.5 g; HCHF: 168.3 ± 14.8 g; p<0.001) and per kg body weight (C: 1.02 ± 0.07 g; HCHF: 3.96 ± 0.21 g; p<0.001). However, expression of mRNA in adiponectin (C: 1.00 ± 0.05; HCHF: 0.60 ± 0.09; p<0.001), PPARγ (C: 1.00 ± 0.03; HCHF: 0.52 ± 0.04; p<0.001) and CIDEA (C: 1.00 ± 0.14; HCHF: 0.55 ± 0.15; p<0.01) was reduced in animals on the HCHF diet compared to controls. There was no difference in the expression of leptin, FABP4, HOXC9 and RIP140 between the two groups. Conclusions: Increased energy intake from a high-fat high-carbohydrate diet in early postnatal and juvenile life promotes adiposity, which in the sternal depot results in endocrine adaptations that would be predicted to prevent metabolic and related dysfunction. Future analysis will examine the other major fat depots to assess whether similar responses are found.