PREPARTUM PROTEIN RESTRICTION DOES NOT ALTER NOREPINEPHRINE-INDUCED THERMOGENESIS OR BROWN ADIPOSE-TISSUE FUNCTION IN NEWBORN CALVES

We examined the effect of prepartum protein restriction on thermogenes is and several aspects of perirenal (brown) adipose tissue (BAT) in ne wborn calves, Lipid synthesis and morphology also were compared betwee n BAT and sternum (white) adipose tissue, During the last 140 d of ges tation, heifers were fed isocaloric diets containing adequate (10.4%) or restricted (average of 6.8%, dry matter basis) levels of protein, B ody condition scores and weight gain during gestation were significant ly lower in heifers fed the restricted-protein diet, However, newborn calf birth weight, calf BAT weight and composition, and calf thermoneu tral metabolic rates were not affected by prepartum protein restrictio n, Similarly, visceral organ weights, except for lung plus trachea, we re not affected (P > 0.10) by prepartum protein treatment, Peak metabo lic rates were not affected (P > 0.10) by prepartum protein treatment and on average were twice the thermoneutral metabolic rates, Consisten t with this, BAT of calves from heifers fed adequate-or restricted-pro tein diets did not differ in lipid synthesis, cellularity, or uncoupli ng protein mRNA:28S rRNA ratios, Although both perirenal and sternum a dipocytes were mostly unilocular, perirenal adipocytes contained numer ous large mitochondria with well-differentiated cristae; sternum adipo cytes contained a small number of mitochondria with poorly developed c ristae, Fatty acid biosynthesis from acetate was high in BAT (55-57 nm ol acetate incorporated.100 mg(-1).h(-1)) but barely detectable in ste rnum adipose tissue, Conversely, fatty acid biosynthesis from glucose was 80-110% higher in sternum adipose tissue than in BAT (4.5 vs 2.1-2 .5 nmol glucose incorporated.100 mg(-1).h(-1)). Thus maternal protein restriction severely affected heifers but had no effect on neonatal ca lf thermogenesis or BAT function.