Donohue M J, Costa D P, Goebel E, Antonelis G A, Baker J D
University of California, Santa Cruz, CA 95064, USA.
Physiol Biochem Zool. 2002 Jan-Feb;75(1):3-18. doi: 10.1086/338284.
Milk ingested by mammalian offspring, coupled with offspring's utilization of this energetic investment, influences survival and growth. A number of studies have examined milk intake in otariids, but few have examined milk intake over the entire lactation period, and none has independently measured energy expenditure concurrent with milk intake. We concurrently examined milk intake, field metabolic rate (FMR), and body composition of 41 pups over the entire lactation interval in 1995 and 1996 on St. Paul Island, Alaska. One hundred two metabolic measurements were obtained with isotope dilution methods. Mean milk intake did not differ annually but increased with age and mass, ranging from 3,400+/-239 to 6,780+/-449 (+/-SE) mL per suckling bout. Milk energy consumption did not vary with age on a mass-specific basis. No differences were detected in milk volume consumed by male and female pups, either absolutely or on a mass-specific basis. Mass-specific FMR peaked during molting, was lowest postmolt, and did not vary by sex. Pups in 1995 had lower FMR than pups in 1996 and were also fatter. Mean milk energy utilized for maintenance metabolism decreased over time from 77% to 43% in 1995 and remained at 71% in 1996. Pup body mass was negatively correlated with the percentage of total body water and positively correlated with the percentage of total body lipid (TBL). Pups increased the percentage of TBL from 16% to 37%. Northern fur seal pups increased energy intake over lactation, while concurrent changes in body composition and pelage condition resulted in mass-specific metabolic savings after the molt.
哺乳动物幼崽摄入的乳汁，以及幼崽对这种能量投入的利用，会影响其生存和生长。许多研究已经考察了海狗科动物的乳汁摄入量，但很少有研究考察整个哺乳期的乳汁摄入量，而且没有一项研究独立测量过与乳汁摄入同时发生的能量消耗。1995年和1996年，我们在阿拉斯加圣保罗岛对41只幼崽在整个哺乳期内的乳汁摄入量、野外代谢率（FMR）和身体组成进行了同步考察。采用同位素稀释法获得了102次代谢测量数据。平均乳汁摄入量每年没有差异，但随年龄和体重增加，每次哺乳的摄入量范围为3400±239至6780±449（±标准误）毫升。按体重比计算，乳汁能量消耗不随年龄变化。无论是绝对量还是按体重比计算，雄性和雌性幼崽消耗的乳汁量均未检测到差异。按体重比计算的FMR在换毛期间达到峰值，换毛后最低，且不随性别变化。1995年的幼崽FMR低于1996年的幼崽，且也更胖。1995年，用于维持代谢的平均乳汁能量随时间从77%降至43%，1996年则保持在71%。幼崽体重与全身水的百分比呈负相关，与全身脂质（TBL）的百分比呈正相关。幼崽的TBL百分比从16%增加到37%。北方海狗幼崽在哺乳期增加了能量摄入，而身体组成和皮毛状况的同时变化导致换毛后按体重计算的代谢节省。
