Armadillo pups rapidly grow a bony carapace, suggesting a large transfer of calcium and phosphorus from mother to pups via milk. Because Ca and P in milk are bound in casein protein micelles, we predicted armadillo milk to be high in protein content. Milk samples (n = 25) from 10 lactating nine-banded armadillos (Dasypus novemcinctus) collected at days 1–6, 14–15, 33–38, and 49–51 after birth were assayed for macronutrient composition (water, fat, protein, sugar, ash, Ca, and P). Gross energy (GE) was calculated from protein, sugar, and fat. Protein concentration (8–11%) was the highest of the milk solids at all time points, and ash (total mineral) values increased from 1.6% to 3.6% and were higher than sugar values (2.4%) after 1 month. Calcium concentration increased from 0.4% to over 1.0% by 1 month of lactation. Calcium and phosphorus were strongly correlated with milk protein (r = 0.796 and 0.815, respectively; P < 0.001). Protein contributed the majority of milk GE over the first 2 weeks of lactation (51%) and was equal to fat after 1 month (both about 47% of GE). The proportion of GE from sugar declined from 14.5% to 6.6%. We suggest that a milk high in protein was an ancestral trait for armadillos that allowed the evolution of a bony carapace by enabling large amounts of Ca and P to be transferred via casein micelles. Based on data from giant anteater (Myrmecophaga tridactyla) milk, a highprotein milk may be ancestral to all Xenarthrans, but this suggestion awaits confirmation from data on the milk of sloths. We suggest that armadillo pups likely catabolize a significant amount of milk protein for metabolic energy.
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Vol. 99 • No. 2