Review paperMechanisms of reduced and compensatory growth
Introduction
Compensatory (or catch-up) growth may be defined as a physiological process whereby an organism accelerates its growth after a period of restricted development, usually due to reduced feed intake, in order to reach the weight of animals whose growth was never reduced. The extent of catch-up growth may be quantified by the “compensatory index” (Fig. 1 ) which can be calculated as the ratio of the difference between weight variation at the end of restricted and compensatory growth periods, respectively, relative to the variation at the end of the restricted growth alone [1]. A value of 100% indicates full recovery, but this is scarcely observed. Generally, the index value is between 50 and 100%. The phenomenon has been extensively studied in several animal species including cattle [2]. The mechanisms involved are still not fully clear.
The magnitude of compensation was indicated to be proportional to the intensity of the previous growth restriction [3], [4]. However, the response varies largely. This is probably explained by the fact that restricted growth can result from several processes, such as various diseases or energy and protein restrictions whose degree may vary considerably. When isoenergetic, but low protein diets are fed, mobilization of protein is greater relative to fat. Low growth rate is also characterized by its length and magnitude, i.e., growth may be maintained, absent or even reversed. Generally, compensation is improved when the duration of growth restriction is short - about 3 mo in cattle - and is not too severe. In addition, compensatory growth in unweaned animals is relatively bad. Finally, very young animals, those severely feed restricted or affected by severe diseases often fail to express compensatory growth [5], [3]. Consequently, the mechanisms underlying reduced and compensatory growth are difficult to understand.
Section snippets
Changes of body composition
Growth results from the differences between tissue synthesis and degradation and losses from the body of energy, nitrogen and minerals due to excretion. During normal development muscle exhibits initially the highest growth rate followed by fat tissue. When growth rates are reduced, there is a coordinate decrease of tissue turnover. However, some tissues react more than others (viscera > adipose tissue > muscle). The empty visceral fraction decreases [6], [7]. Because fat deposition is more
Effects on performances and body composition
Compensatory growth requires an adaptation period whose duration varies from one species to another. In ruminants it takes about one month. Then, compensation results mainly from higher feed intake. There is limited literature reporting changes of live weight gain and metabolic adaptations during the compensatory growth phase in cattle [27], [28], [29], [30], [31], [32], [33]. Compensatory growth rates are cubic in nature (Fig. 2). When growth restriction is moderate (e.g., about 300 g/d in
Conclusions
Compensatory growth is a coordinated response to realimentation, initially characterized by high plasma levels of GH. This could be responsible for the depositition of lean tissue in compensating animals. A rapidly established euinsulinic state could play a key role in the initiation of the compensatory growth and may alleviate the resistance of the somatotropic axis to GH. Results concerning IGF-I and thyroid hormones are more conflicting. Their plasma concentrations during compensatory growth
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