Some pig producers manage the supply of replacement breeding gilts by operating a within herd multiplication programme in tandem with their genetic supplier. I believe that it is important for producers to maintain collaboration with their genetic supplier and their supplying vet and nutritionist if this business strategy is adopted. In the case of the producers using the criss-cross system it is good to understand the genetic balance in each cohort of replacement gilts produced from the regularly alternating supply of Dam-line genetics.
The reason for this is simple it introduces variation in the breeding and feeding herd performance. To understand this variation and to prevent it from misleading the interpretation of performance analysis it helps to know what the balance is at any given time and to relate this to the cyclical variation year on year.
In my Solutions page menu there is a page called Useful Stuff…on this page you will find a Genetic Criss-Cross Table that demonstrates the genetic balance in two and three way programmes and the progression from a two to three way programme.
The time lag between the start of each new genetic mix and balance which is driven by the introduction of the (changeover) Dam-line semen is usually 6 months on most farms. The population needs careful monitoring to identify the animals with the correct mix. Where the management strategy includes a parity driven selection criteria the time lag is still possible providing there are enough designated GP sows in the older parities. This needs scrutiny otherwise the genetic balance will slip towards one or other of the genetic lines being employed.