Animal Breeding Basics - genetics or environment?

An individual animal can end up in the poor end of the distribution for a number of reasons.  For example:

• It could have been born from a young dam.
• It could have been born a twin.
• Its mother could have had little milk
• It could have been affected by disease.
• It could have inherited poor genes from its parents.

The first four points are all controlled by the environment (E).  The last one is about genetics (G).

Similarly an individual animal in the good end of the distribution could be there because of a good environment (E) or because it had inherited good genes (G).

It’s important to know which of the traits we measure are caused by G and which by E. 

So we use this little formula of P = G + E.  This says that the phenotype (P) of the animal is made up of genetics (G) and the environment (E).

When we buy animals for breeding, we need to make sure we are buying G and not E, as the effects of E are not passed on and will disappear in the next generation. 

Only the effects of G will be passed on and are not lost, even when the E is poor.

In poor environments, e.g. when animals are starved, their full genetic potential cannot be expressed, but their genes are unaffected and can be exploited when the E improves, and to be passed on to their offspring, regardless of the E.

Genetic/environment interaction

This is where certain animals do better in some environments than in others and is called a genetic/environment interaction.

So breeders become concerned that selecting in one environment will not be best for animals to perform in a different environment.

Examples:

• Will the daughters of dairy bulls bred for intensive grain-fed systems in the USA perform well in New Zealand when pasture fed?
• Will rams of mountain sheep breeds produce hardy progeny when run on the mountain grazings?

Regression to the mean – a surprise

• If you breed from an individual that appears to be well below the mean, you may be surprised to find how good its offspring perform.
• Similarly, if you breed from an individual well above the mean, you may be disappointed with its offspring.
• Don’t be surprised as this is called “regression to the mean”, and happens because we did not have an accurate measure of the individual’s G that we chose as parents.  We were fooled by E.
• So there may be some bargains in animals from flocks and herds with good genetics if they don’t look too good because of environmental reasons.  They will breed good offspring themselves. You may often hear people say “they shift well”!
• On the contrary, beware of buying good-looking individuals from flocks or herds with ordinary genetics.  You’ll certainly pay for good E effects that you may not be able to maintain.
• The basic message is to buy on records (an indicator of genotype) and not solely on looks (phenotype).