Prepartum protein restriction does not alter norepinephrine-induced thermogenesis or brown adipose tissue function in newborn calves.
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We examined the effect of prepartum protein restriction on thermogenesis and several aspects of perirenal (brown) adipose tissue (BAT) in newborn calves. Lipid synthesis and morphology also were compared between BAT and sternum (white) adipose tissue. During the last 140 d of gestation, heifers were fed isocaloric diets containing adequate (10.4%) or restricted (average of 6.8%, dry matter basis) levels of protein. Body condition scores and weight gain during gestation were significantly lower in heifers fed the restricted-protein diet. However, newborn calf birth weight, calf BAT weight and composition, and calf thermoneutral metabolic rates were not affected by prepartum protein restriction. Similarly, visceral organ weights, except for lung plus trachea, were not affected (P > 0.10) by prepartum protein treatment. Peak metabolic rates were not affected (P > 0.10) by prepartum protein treatment and on average were twice the thermoneutral metabolic rates. Consistent with this, BAT of calves from heifers fed adequate- or restricted-protein diets did not differ in lipid synthesis, cellularity, or uncoupling protein mRNA:28S rRNA ratios. Although both perirenal and sternum adipocytes were mostly unilocular, perirenal adipocytes contained numerous large mitochondria with well-differentiated cristae; sternum adipocytes contained a small number of mitochondria with poorly developed cristae. Fatty acid biosynthesis from acetate was high in BAT (55-57 nmol acetate incorporated.100 mg-1.h-1) but barely detectable in sternum 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 calf thermogenesis or BAT function.
