It involves mating of related animal for following purposes
1) To increase homozygosity in progency.
2)To develop inbread line.
3)To keep animals pure breed.

This system is not adopted commercially for the following adverse effects
a) Decreases mean litter size with increase in age of pigs.
b) Decrease in post weaning weight.
c) Decline in milking and mothering ability of sows.
d) Delayed sexual maturity in pigs.
e) Reduce prolificacy.

It consists of mating of unrelated animals and systems of it are being extensively used for achievement of good results with regards to performance of pigs. Following are the merits of this method.
a) Fewer embryonic losses.
b) Increase in litter size and weaning weight.
c) Increase in growth rate.
d) Early age of maturity.
e) Increase efficiency of feed conversion.
f) Good mothering and milking ability.

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