Abstract: Many researchers can not distinguish between the two terms, instantaneous growth rate and geometric growth rate. They use the following equation of calculating geometric growth rate to calculate animal’ s postnatal instantaneous growth rate: IGR = lnW₂-lnW₁/t₂-t₁
This misuse began in 1945 when Brody wrote the paper,“Time relation of growth of individuals and populations”, and was repeated by Lackey (1967). Since then, more and more researchers have repeated the same mistake. In this paper, the authors redefine the instantaneous growth rate as the first derivative of given measurements to time, that is IGR =dW / dt Here, W may be any measurement such as body weight, tail length, and so on.. The authors recommend procedures of calculating the instantaneous growth rate. First, the growth model should be established by fitting a sigmoidal equation to the observed growth data because animal’ s growth in most cases is sigmoidal. Second, find the first derivative, the equation representing the relationship between instantaneous gmMh rate and time. Third, use the equation to calculate instantaneous growth rate. Table 1 gives out the equation of calculating instantaneous growth rate for some growth models in common use. To show how to calculate instantaneous growth rate by the above procedures, growth data of body weight of male striped hamster ( Cricelulus barabensis) are used as examples, and the results are given out in table 2.

Key words: Instantaneous growth rate, Geometric growth rate, Growth model, First derivative

摘要： 针对文献中有关瞬时生长率概念和计算方法的错误，将瞬时生长率重新定义为给定生长指标对生长时间的一阶导数。并建议，首先采用曲线回归方法建立生长模型—生长指标关于生长时间的函数，然后通过求一阶导数得到瞬时生长率随生长时间变化的表达式，利用该表达式计算任意时刻的瞬时生长率。采用黑线仓鼠的例子说明该计算过程。

关键词: 瞬时生长率, 几何增长率, 生长模型, 一阶导数