**9. Growth rate and reproduction**

Information on the effects of selection for body weight or growth rate on reproductive fitness in cattle is unfortunately limited [27]. In a fundamental theorem of natural selection in the 1930s it was already postulated that reproductive fitness and body weight will be near the peak of fitness in a natural population [61]. However, when selection for growth takes place, the population is no longer in a natural equilibrium, so the reproductive fitness may in fact decline when the mean of a population is moved in either direction due to selection pressure [62]. The antagonistic relationship between fertility and milk production in dairy cows and the resource allocation theory support this theory [63]. The general consensus is that selection for increased body weight or growth rate may have an adverse effect on fertility [27] for the following reasons namely:


There is therefore a concern that selection for high growth rate might have negative effects on the fertility of cows [64]. However, contrasting results have been published which indicate that cows with a high pre-weaning growth, reared more calves over their lifetime, had lower calf mortalities and also calved earlier than cows with lower pre-weaning growth [65]. In another unrelated study the reproductive performance of Angus females selected for a high growth rate was similar to those of females where there was no deliberate selection pressure at all. The EBV trends obtained and presented in **Figures 4** and **5** for growth and reproduction traits in Bonsmara cows, indicate a negative correlation and warns against excessive selection for growth traits in extensive beef cattle, especially if the natural resources are limited [22].
