VARIATION

Standard deviation of BVs (each trait and breed)
Inbreeding management
Population size and genetic exchange
Genetic importation
Consideration of molecular genetic (ex: Scrapie genotypes)

STANDARD DEVIATION OF EBVs

Trait variation allows quick improvement when the variation range is large and only small improvement when variation range is narrow. Trait variation depends on the trait and the breed. (e.g. litter size in Romanov v/s in Dorset)

TIPS FOR GOOD INBREEDING MANAGEMENT

GenOvis Mating module is a good tool to follow and control inbreeding evolution within the flock

		Tips	Example (for a 100 ewes flock – 1 lambing per year)
		Use enough rams each year (based on flock size)	5 rams
		Define the number of mates / ram	20 mates / ram
		Keep a maximum number of rams / sire	1-2 rams maximum / sire
		Use GenOvis mating module	Aim < 6,25% of inbreeding for the mates

You need a balance between genetic gain and inbreeding evolution

Aim for less than 1% every 10 years

INBREEDING EVOLUTION OF MAIN EVALUATED BREEDS

POPULATION SIZE AND GENETIC EXCHANGE

A minimum of 400 ewes is required to manage the virtual flock as a closed flock

For smaller groups, we should be careful with inbreeding management. This usually slows down the genetic gain within the group.

Small Size Population

Small size population (< 200 ewes) consequences in selection:

–Inbreeding management more important = Limit genetic gain

–Genetic import = Genetic gain influenced by import

Large Size Population

Aim a purebred breeders group of > 400 ewes

–Favor genetic exchanges

–Your own genetic gain is related to other breeders’ gain

Strenght of the Breders Group

Alone we can do so little; together we can do so much.

GENETIC IMPORT

Semen import needs to be followed to identify from which country/flock we have advantage to import semen.

ADVANTAGES

–Increase genetic variability

–Improve genetic merit (but not always)

–Improve some specific breed traits

DISADVANTAGES

–Possible loss on some traits

–Costly

IMPORTANT

Evaluate the genetic merit of animals imported for all traits

CONSIDERATION OF MOLECULAR GENETICS

The arrival of molecular genetics is a good improvement in sheep selection. This technology will increase the accuracy of breeding values.

The use of scrapie genotype to make selection may also impacts the genetic gain. For example, keeping only RR rams will remove from selection other rams that may bring high genetic gain because of their scrapie genotype (e.g. QQ).