Background and Aims: Brown adipose tissue (BAT) has been identified as a potential target to combat obesity. This is due to its propensity to expend large amounts of energy via non-shivering thermogenesis, a process that is mediated by Uncoupling Protein (UCP) 1 (1). In sheep, during postnatal development, BAT is rapidly replaced by white adipose tissue, an adaptation determined in part by the maternal metabolic and endocrine environment (2). One dietary factor that may influence this process is the milk content of conjugated linoleic acid (CLA), specifically the cis-9, trans-11 isomer, which has been shown to promote the abundance of UCP1 in vitro (3). The aim of this study was to determine whether maternal dietary supplementation of canola oil, to increase the amount of the cis-9, trans-11 isomer in the milk, would promote the retention of BAT during postnatal development. Methods: With UK Home Office approval, from the first day of lactation, sheep were fed daily either a standard diet (control, n=8) of concentrate (1.5 kg/day) with hay (1.5 kg/day) or the same diet plus 3% canola oil (canola; n=8). Each mother raised 2 lambs. Milk samples were collected from each mother at 7 and 28 days of lactation, immediately before one lamb was euthanased with an intravenous injection (Pentobarbital Sodium, 200mg/kg body weight) and tissue sampled. Samples of perirenal adipose tissue were weighed and fixed in 10% formalin for immunohistochemical (IHC) analysis. Samples were sectioned and stained with UCP1 antibodies. The total area of tissue and the area stained were measured, and the percentage of UCP1 staining calculated. Values are means ± S.E.M. compared by Mann-Whitney test (IHC) or unpaired t test (milk analysis). Results: Supplementation of the maternal diet with canola oil resulted in an increase of cis-9, trans-11 CLA in the milk at 28 days (control, n=8, 6.3±0.5 mg/g fat; canola, n=8, 10.9±0.5 mg/g fat; p<0.0001) but not 7 days of lactation (control, n=8, 10.7±0.9 mg/g fat; canola, n=8, 12.5±0.7 mg/g fat). The Canola group has increased amounts of UCP1, visualised by IHC (expressed as a percentage of tissue stained with UCP1 antibodies) compared with controls at 28 (control, n=9, 13.9%±1.2; canola, n=8, 29.4%±3.8; p=0.0002) but not 7 days of age (control, n=6, 37.8%±3.2; canola, n=6, 37.0%±3.5). Conclusions: Maternal supplementation of canola oil during lactation delays the rate of loss UCP1 from perirenal adipose. The mechanisms mediating this response are currently being examined.