Predicted increases in global average temperature are physiologically trivial for most endotherms. However, heat waves will also increase in both frequency and severity, and these will be physiologically more important. Lactating small mammals are hypothesized to be limited by heat dissipation capacity, suggesting high temperatures may adversely impact lactation performance. We measured reproductive performance of mice and striped hamsters (Cricetulus barabensis), including milk energy output (MEO), at temperatures between 21 and 36 °C. In both species, there was a decline in MEO between 21 and 33 °C. In mice, milk production at 33 °C was only 18% of that at 21 °C. This led to reductions in pup growth by 20% but limited pup mortality (0.8%), because of a threefold increase in growth efficiency. In contrast, in hamsters, MEO at 33 °C was reduced to 78.1% of that at 21 °C, yet this led to significant pup mortality (possibly infanticide) and reduced pup growth by 12.7%. Hamster females were more able to sustain milk production as ambient temperature increased, but they and their pups were less capable of adjusting to the lower supply. In both species, exposure to 36 °C resulted in rapid catastrophic lactation failure and maternal mortality. Upper lethal temperature was lowered by 3 to 6 °C in late lactation, making it a critically sensitive window to high ambient temperatures. Our data suggest future heat wave events will impact breeding success of small rodents, but this is based on animals with a long history in captivity. More work should be performed on wild rodents to confirm these impacts.

对于大多数吸热，全球平均温度的预测升高在生理上是微不足道的。但是，热波的频率和严重性也会增加，这在生理上将更为重要。假定哺乳期的小型哺乳动物受散热能力的限制，这表明高温可能会对泌乳性能产生不利影响。我们测量了小鼠和条纹仓鼠（Cricetulus barabensis），包括21至36°C之间的牛奶能量输出（MEO）。在这两个物种中，MEO均在21至33°C之间下降。在小鼠中，33°C时的产奶量仅为21°C时的产奶量的18％。由于生长效率提高了三倍，这使幼崽的生长减少了20％，但幼崽的死亡率却有限（0.8％）。相反，在仓鼠中，将33°C的MEO降低至21°C时的78.1％，但这导致了显着的幼仔死亡率（可能是杀婴剂），幼仔生长降低了12.7％。随着环境温度的升高，仓鼠雌性更有能力维持产奶量，但仓鼠和幼崽的适应能力却较低。在这两个物种中，暴露于36°C都会导致快速的灾难性泌乳衰竭和产妇死亡率。哺乳后期，最高致死温度降低了3至6°C，使其成为对高环境温度极为敏感的窗口。我们的数据表明，未来的热浪事件将影响小型啮齿动物的繁殖成功，但这是基于圈养历史悠久的动物。应该对野生啮齿动物进行更多的工作，以确认这些影响。