Optimum structure for genetic improvement of Angora rabbits

A breeding structure comprised of nucleus, multiplier, reproducer and producer tiers for Angora rabbits has been optimised. With the assumptions of age at maturity in males and females as 5 months, reproductive ability of females as 16 progenies per year, a mating capacity of 1 male with 7 females, and a more or less uniform age distribution of breeding individuals, it was found that in the nucleus males should be used for breeding for 4 months and females for 6 months to maximise genetic progress. The methodology for computing the flow of genetic progress from nucleus to other tiers has been worked out, and the optimal proportionate contributions from males and females of one tier to produce the males and females of the next tier have been determined. At the start the optimal fraction of animals going to the multiplier and reproducer changes until the scheme reaches a steady state, after which the genetic gain per unit of time is the same in all the 4 tiers. With a constant population size at the producer level it is shown that the rate of flow of genetic progress is directly related to the size of the nucleus, i.e. the larger the size of the nucleus the faster the flow of genetic progress. The optimum size of nucleus to achieve economically efficient genetic gains will be at a point where the marginal cost for increasing the nucleus size is equal to the increase in economic returns due to the reduction in time lag (the difference between nucleus and othertiers).