Short-term responses to selection for parameters of the allometric-autoregressive model

Author: M.M. Scholtz, C.Z. Roux, D.S. de Bruin and S.J. Schoeman
Year: 1990
Issue: 2
Volume: 20
Page: 57 - 64

The allometric-autoregressive model describes growth accurately and is useful in the characterization of growth responses. Hence, the potential of the model for selection purposes was investigated. Rats were used in a selection experiment, where selection was practised for slope (b) and intercept (In a) of the allometric function: w = In a + bv [where w = In (body mass) and v = In (cumulative feed intake)], and p, the autoregression slope of In (cumulative feed intake). Facilities for five selection groups of 40 rats each were available. Both upward and downward within family selections were practised for In a and b, and only downward selection for p. In the short term, selection for In a and b resulted in good direct responses, and it appears that the model can be used to alter the shape of the growth and efficiency curve by selection. The realized heritabilities correspond to the heritabilities of previous studies. Although the heritability estimate of p is low, a moderate selection response was realized in the short term. Only the correlated responses to selection for b seem to be of any significance during the four generations of selection. Efficiency during the growth phase in which selection was practised increased markedly (17%), while total efficiency, which includes the estimated efficiency from conception, also increased (13%). Furthermore, selection for b led to an increased growth rate (15%) and a slight increase in body mass (8%), whilst intake tended to decrease (-5%). Normally intake tends to increase as growth rate and mass increase.



Keywords: : Growth, Allometric-autoregressive model, correlated response, Efficiency, realized heritability, selection
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