Lepczyk C A, Caviedes-Vidal E, Karasov W H
Department of Wildlife Ecology, University of Wisconsin-Madison, 53706, USA.
Physiol Zool. 1998 Sep-Oct;71(5):561-73. doi: 10.1086/515965.
We used nestling house sparrows (Passer domesticus) under laboratory conditions to test for modulation of digestive efficiencies during periods of low and high food intake and tested the hypothesis that nestlings would exhibit compensatory changes in digestive efficiency following a period of food restriction. During the low intake period, nestlings were held at constant body mass for 48 h beginning on either day 3 or day 6 of life by feeding them at 50% of control rations. After 48 h of food restriction, nestlings were fed as much as they could consume, allowing the nestlings restricted at day 6 (early restriction not assessed) to consume 14% more food than control nestlings. For nestlings restricted at day 6 apparent dry mass assimilation of the entire diet was found to be 5% and 8% lower during food restriction and realimentation, respectively, compared with control nestlings that were not under- or overfed. There were no significant differences in radiolabeled starch assimilation efficiencies between control and restricted nestlings. Starch assimilation efficiencies remained constant from 3 d of age onward in control nestlings. Total starch extracted was lower during food restriction but reached a rate similar to that of control nestlings during the realimentation period. Passage times (time of first defecation, mean retention time, and mode passage time) measured with an indigestible marker were longer during food restriction and shorter during realimentation, relative to control nestlings. During realimentation there was no difference in intestinal rates of hydrolysis or mediated uptake of L-leucine compared with control nestlings. The main effect of changing food intake was apparently to alter flow rate, and hence retention time, causing slight changes in digestive efficiency. Thus, nestlings did not exhibit compensatory changes in digestion rates as implied by the hypothesis. Our finding of a lower dry mass assimilation efficiency and similar total starch assimilation during realimentation (relative to controls) helps explain why nestling house sparrows do not display compensatory growth, despite higher food intake. Our results indicate that the gut has little spare capacity to deal with increased food intake during growth following food restriction.
我们在实验室条件下使用家麻雀雏鸟（Passer domesticus）来测试低食物摄入量和高食物摄入量期间消化效率的调节情况，并检验了这样一个假设：雏鸟在经历一段食物限制期后，消化效率会出现补偿性变化。在低摄入量时期，雏鸟从出生第3天或第6天开始，通过以对照食量的50%喂食，使其体重在48小时内保持恒定。在48小时的食物限制期过后，给雏鸟尽可能多的食物，结果发现第6天开始受限的雏鸟（未评估早期限制情况）比对照雏鸟多消耗14%的食物。与未经历食物不足或过量的对照雏鸟相比，对于第6天开始受限的雏鸟，在食物限制期和再喂食期，整个饮食的表观干物质同化率分别低5%和8%。对照雏鸟和受限雏鸟之间放射性标记淀粉的同化效率没有显著差异。对照雏鸟从3日龄起淀粉同化效率保持恒定。在食物限制期提取的总淀粉量较低，但在再喂食期达到了与对照雏鸟相似的速率。与对照雏鸟相比，用不可消化标记物测量的通过时间（首次排便时间、平均保留时间和通过时间模式）在食物限制期更长，在再喂食期更短。在再喂食期，与对照雏鸟相比，肠道水解速率或L-亮氨酸的介导摄取没有差异。改变食物摄入量的主要影响显然是改变流速，进而改变保留时间，导致消化效率略有变化。因此，雏鸟并未如假设所暗示的那样表现出消化率的补偿性变化。我们发现在再喂食期（相对于对照组）较低的干物质同化效率和相似的总淀粉同化率，这有助于解释为什么家麻雀雏鸟尽管食物摄入量增加，但并未表现出补偿性生长。我们的结果表明，在经历食物限制后的生长过程中，肠道几乎没有多余的能力来应对增加的食物摄入量。
