Maternal nutrient restriction during critical stages of gestation (e.g. mid-gestation, coincident with maximal placental growth) compromises fetal growth and development⁽ Footnote ^{1 )}. However, late gestational protein supplementation in twin-bearing pregnancies improves lamb vigour, immune competence and colostrum production⁽ Footnote ^{2 )}. The extent to which nutritional supplementation of the mother with protein in the form of fishmeal can promote expression of the thermogenic brown adipose tissue-specific uncoupling protein (UCP) 1 is unknown. Thus, the present study aimed to determine whether protein supplementation of the maternal diet at defined stages of gestation promotes the fetal growth or the regulation of mitochondrial protein abundance in brown adipose tissue.

Twenty-eight twin-bearing sheep of similar body weight and parity were randomly allocated into four feeding groups from 10 d of gestation. Each animal was fed a standard control diet, which was supplemented with fishmeal (66% (w/w) crude protein plus an equal amount of molasses to aid palatability) and fed to each of the three treatment groups during early (10–40 d; n 7), mid- (40–70 d; n 7) or late (110 d; n 7) gestation. Each mother was then humanely killed with an overdose of barbiturate (100 mg pentobarbital sodium/kg; Euthanal) at 140 d of gestation to enable fetal tissue sampling. mRNA and protein abundances were determined using fully-validated real-time RT–PCR techniques and antibodies respectively. Results, in arbitrary units (au), are expressed as a percentage of a reference sample present on all quantitative PCR plates and SDS–PAGE gels. Significant differences in relation to nutritional supplementation were determined by GLM analysis.

Protein supplementation had no effect on fetal body, placental or organ weights. UCP1 expression of the protein (but not mRNA) was increased in offspring supplemented during mid-gestation (control 79 (se 10) au v. 126 (se 140 au; P<0.05) despite a reduction in total mitochondrial protein. UCP2, PPARγ, PPARγ co-activator-1a (PGC-1a), glucocorticoid receptor (GR), 11β-hydroxysteroid dehydrogenase (11β HSD)-1 and -2, β-adrenergic receptor 3 (β-AR 3) and AMP-activated protein kinase α2 (AMPK α2) mRNA levels were all unaffected by fishmeal supplementation.

Increased UCP1 expression with protein supplementation specifically during mid-gestation is likely to improve thermogenesis in the newborn. However, this adaptation appears unrelated to sympathetic activation or glucocorticoid stimulation and is, therefore, likely to be mediated by translational modification and/or stabilisation of UCP1.