Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada.
PLoS One. 2011 May 11;6(5):e19487. doi: 10.1371/journal.pone.0019487.
Although evidence from domestic and laboratory species suggests that reproductive experience plays a critical role in the development of aspects of lactation performance, whether reproductive experience may have a significant influence on milk energy transfer to neonates in wild populations has not been directly investigated. We compared maternal energy expenditures and pup growth and energy deposition over the course of lactation between primiparous and fully-grown, multiparous grey seal (Halichoerus grypus) females to test whether reproductive experience has a significant influence on lactation performance. Although there was no difference between primiparous females in milk composition and, thus, milk energy content at either early or peak lactation primiparous females had a significantly lower daily milk energy output than multiparous females indicating a reduced physiological capacity for milk secretion. Primiparous females appeared to effectively compensate for lower rates of milk production through an increased nursing effort and, thus, achieved the same relative rate of milk energy transfer to pups as multiparous females. There was no difference between primiparous and multiparous females in the proportion of initial body energy stores mobilised to support the costs of lactation. Although primiparous females allocated a greater proportion of energy stores to maternal maintenance versus milk production than multiparous females, the difference was not sufficient to result in significant differences in the efficiency of energy transfer to pups. Thus, despite a lower physiological capacity for milk production, primiparous females weaned pups of the same relative size and condition as multiparous females without expending proportionally more energy. Although reproductive experience does not significantly affect the overall lactation performance of grey seals, our results suggest that increases in mammary gland capacity with reproductive experience may play a significant role in the age-related increases in neonatal growth rates and weaning masses observed in other free-ranging mammals.
尽管来自国内和实验室物种的证据表明，生殖经验在泌乳表现的某些方面的发展中起着关键作用，但生殖经验是否对野生种群中新生仔的乳汁能量传递有重大影响尚未直接研究。我们比较了初产和完全成熟、多产的灰海豹（Halichoerus grypus）母兽在哺乳期的能量消耗和幼仔生长及能量沉积，以检验生殖经验是否对泌乳表现有重大影响。尽管初产母兽的乳汁成分没有差异，因此，在泌乳早期或高峰期的乳汁能量含量也没有差异，但初产母兽的每日乳汁能量输出明显低于多产母兽，表明乳汁分泌的生理能力降低。初产母兽似乎通过增加哺乳努力有效地弥补了产奶率较低的问题，从而实现了与多产母兽相同的相对乳汁能量传递给幼仔的速率。初产母兽和多产母兽在为支持泌乳成本而动员初始体能量储备的比例上没有差异。尽管初产母兽相对于乳汁生产将更多的能量储备分配给母体维持，而不是多产母兽，但差异不足以导致能量向幼仔传递的效率有显著差异。因此，尽管初产母兽的乳汁生产生理能力较低，但它们仍能以与多产母兽相同的相对大小和条件断奶幼仔，而不会不成比例地消耗更多的能量。尽管生殖经验不会显著影响灰海豹的整体泌乳表现，但我们的研究结果表明，随着生殖经验的增加，乳腺容量的增加可能在其他自由放养哺乳动物中观察到的与年龄相关的新生仔生长率和断奶质量的增加中起着重要作用。
