Oftedal O T
Department of Zoological Research, National Zoological Park, Smithsonian Institution, Washington, DC 20008.
J Dairy Sci. 1993 Oct;76(10):3234-46. doi: 10.3168/jds.S0022-0302(93)77660-2.
Although lactation is accompanied by increased nutrient demands for milk synthesis, many species of bears, true seals, and baleen whales fast for much or all of lactation. Large body mass in these species confers the advantage of greater stores of fat and protein relative to rates of milk production. Given the constraints on substrate availability during fasting, the milks of fasting mammals are predicted to be low in carbohydrate, protein, and water and to be high in fat. The milks of bears, true seals, and baleen whales conform to this prediction. Mammals that lactate while fasting may lose up to 40% of initial BW. The production of milk entails the export of up to one-third of body fat and 15% of body protein in the dormant black bear and in several seal species, which greatly depletes maternal resources and may represent a physiological threshold, because higher protein and fat outputs have only been measured in species that start feeding. The low K:Na ratio of seal and whale milks and the low Ca:casein and inverse Ca:P ratios in seal milks are unusual and warrant further study.
尽管哺乳伴随着对乳汁合成的营养需求增加，但许多熊类、真海豹和须鲸在大部分或整个哺乳期都禁食。这些物种的大体型带来了相对于产奶速率而言更大的脂肪和蛋白质储存优势。考虑到禁食期间底物可用性的限制，预计禁食哺乳动物的乳汁碳水化合物、蛋白质和水分含量较低，而脂肪含量较高。熊、真海豹和须鲸的乳汁符合这一预测。禁食时哺乳的哺乳动物可能会损失高达初始体重40%的重量。在冬眠的黑熊和几种海豹物种中，产奶需要输出高达三分之一的体脂和15%的体蛋白，这极大地消耗了母体资源，可能代表了一个生理阈值，因为只有在开始进食的物种中才测量到更高的蛋白质和脂肪输出量。海豹和鲸类乳汁的低钾钠比以及海豹乳汁中低钙酪蛋白比和反钙磷比很不寻常，值得进一步研究。
