Data from: Lower haematocrit, haemoglobin and red blood cell number in zebra finches acclimated to cold compared to thermoneutral temperature

Thermoregulation constitutes an important share of the energy budget of endotherms. Elevated thermoregulatory requirements must be met by oxygen supply through the blood, as heat is produced mainly via aerobic processes. In contrast to mammal studies, it remains unclear whether elevated thermoregulatory needs are followed by changes in haematological variables in birds. We investigated haematocrit (HCT), haemoglobin content per volume of blood (HGB), number of red blood cells (RBC), and size of the erythrocytes (RBC) in zebra finches (Taeniopygia guttata) acclimated to either cold or thermoneutral ambient temperatures under laboratory conditions. Seventy-nine females were maintained for six weeks either in cold (T = + 12 °C) or thermoneutral (T = + 32 °C) ambient temperature prior to blood collection. On average, HGB, HCT and RBC were significantly lower by about 10% in cold acclimated compared to thermoneutral acclimated birds. Only RBC was not different between the two acclimation temperatures. Mean HCT, one of the most commonly measured haematological variable for example was 53 ± 0.9 % (LSM ± s.e.m) in thermoneutral and 49 ± 0.8 % (LSM ± s.e.m) in cold acclimated zebra finches. On first sight, the observed lower values for three out of the four determined haematological variables in response to acclimation to cold question oxygen supply to be indeed a limiting factor for heat production. However, higher demands of oxygen supply due to increased thermoregulation in birds may instead require specific optimisation of blood viscosity and modulation by other cardiovascular properties. Nucleated red blood cells in birds may pose different strain on blood viscosity compared to non-nucleated mammalian erythrocytes and explain the contrasting response in haematological variables to temperature acclimation between birds and mammals.

体温调节在恒温动物（endotherms）的能量收支中占据重要比重。由于机体产热主要依赖有氧代谢过程，当体温调节需求升高时，必须通过血液运输的氧气来满足该需求。与哺乳动物相关研究不同，目前仍不清楚鸟类在体温调节需求升高时，其血液学指标是否会发生相应变化。本研究在实验室条件下，对分别驯化于低温或热中性环境温度的斑胸草雀（Taeniopygia guttata）开展了四项血液学指标检测，包括红细胞比容（haematocrit, HCT）、每单位体积血液血红蛋白含量（haemoglobin content per volume of blood, HGB）、红细胞计数（red blood cells, RBC）以及红细胞体积。

本研究共纳入79只雌性斑胸草雀，在采血前分别于低温（12℃）或热中性（32℃）环境温度下驯化饲养6周。结果显示，与热中性驯化组相比，低温驯化组的HGB、HCT及红细胞计数平均降低约10%，仅红细胞体积在两组驯化温度下无显著差异。以最常用的血液学指标之一HCT为例，热中性驯化组斑胸草雀的平均HCT为53±0.9%（最小二乘均值±标准误，LSM ± s.e.m），低温驯化组则为49±0.8%（LSM ± s.e.m）。

乍看之下，低温驯化下四项血液学指标中有三项出现降低，这似乎对“氧气供应是产热的限制因素”这一观点提出了质疑。但鸟类因体温调节增强而产生的更高氧气供应需求，反而可能需要通过优化血液黏度以及调控其他心血管特性来满足。与哺乳动物的无核红细胞相比，鸟类的有核红细胞对血液黏度的影响存在差异，这或许可以解释鸟类与哺乳动物在温度驯化下血液学指标响应的差异。