14.6.4 Monitoring the rate of inbreeding
- Tessa Jacobs
- Kor Oldenbroek
To avoid problems with inbreeding, the occurrence of recessive genetic defects and inbreeding depression, the rate of inbreeding ΔF should be less than 0,5 % per generation. Internationally it is agreed that a 0,5 % inbreeding rate is the maximum acceptable value. The higher the estimated inbreeding rate per generation, the higher the chance for inbreeding problems as is illustrated below:
determine the average inbreeding coefficient on annual basis considering all animals that were born in that year. That is the fastest way of identifying changes in the annual rate of inbreeding pattern.
Definitions
Rate of inbreeding is expressed per generation, but can be determined per year for monitoring changes in genetic diversity.
The generation interval for male and female parents is the average age of the parent when its replacement is born. The generation interval for the population is then the average of these two values since males and females each contribute half the genes to renewing the population.
The inbreeding coefficients are averaged over generation 1 and the subsequent generation 2. The difference is divided by the average generation interval:
ΔF = (F2 –F1) / GI,
where F2 and F1 are the average inbreeding coefficients and GI is the generation interval.
A short generation interval accelerates not only the genetic improvement, but also the inbreeding rate per year. In small populations where genetic improvement has not the highest priority, a long generation interval is recommended. Then, e.g. more time is available to monitor the results of mating schemes and to realize still matings that were intended, but did up to now not result in offspring.
For a reliable calculation of the inbreeding rate it is important that pedigrees are complete over 5 generations of ancestors. Incompleteness leads to an underestimation of inbreeding coefficients and inbreeding rates.