Effects of prepartum dietary copper on thermogenic capacity of neonatal lambs

Abstract

To examine the effects of prepartum dietary Cu on thermometabolism in neonatal lambs, twin-bearing ewes were assigned on d5O of gestation to diets containing 3.25, 10, and 20 mg Cu/kg DM (n = 8). Within each twin pair, lambs were assigned at birth to a cold (6'C) or warrn (28C) environmental chamber for 48 h. Blood samples collected from ewes at birth and 21, 14, 7 d prior to birth, and from lambs at birth and 48 h of age were analyzed for plasma Cu, ceruloplasmin, triiodothyronine (T3), thyroxine (T4), cortisol, glucose, and nonesterified fatty acids. At 48 h of age, lambs were euthanized and tissues collected. Plasma ceruloplasmin activity was not affected by Cu treatment, although plasma Cu concentration tended (P = . 11) to be higher in ewes fed the high-Cu diet than the low-Cu diet. Moreover, prenatal Cu treatment did not affect liver Cu concentrations in lambs at 48 h of age. Plasma T3 and T4 concentrations were 21 and 24% lower (P < .01) in low-Cu compared to high-Cu ewes. Birth weights were not affected by prepartum dietary Cu treatment, however, at 48 h of age lambs born to high-Cu ewes were 20% lighter (P <.05)than lambs born to low-Cu ewes. Cytochrome c oxidase (COX) activities, and lipid and protein contents of BAT were not affected by Cu treatment. However, DNA content and UCP MRNA levels were higher in lambs born to high-Cu than low-Cu ewes. Cold exposure, as expected, increased COX activity and UCP MRNA, and reduced lipid content of BAT. Despite having higher UCP MRNA levels in BAT, .high-Cu treatment resulted in lower rectal temperatures at birth and at 48 h of age in cold-exposed lambs. Lamb plasma T3 and T4 increased due to cold exposure, however, TA concentrations were lower in high-Cu lambs compared to low-Cu lambs. These data suggest that low-Cu impaired thermogenic capacity of BAT (i.e. reduced UCP MRNA); however lambs born to high-Cu ewes were more prone to hypothermia during cold exposure than lambs born to low-Cu ewes due to lower body weights and lower plasma T3 concentrations.