Back in the Hello and Welcome! post I alluded to the intense maths behind successful breeding. Here is your first formula:
P = G + E
Scarey, isn’t it?! Though I stress that this is an oversimplified equation.
Phenotype = Genotype + Environment
In other words:
Phenotype is the result of genetic factors (the genotype) and nongenetic factors (the environment).
Not all phenotypes have nongenetic influences—a pup born with brindle coat genes is going to be brindle whether born in a temperate zone or the heart of a desert. But many phenotypes do, and this should be considered when embarking on a breeding programme.
Consider exceptional stud stock, known to produce high quality progeny over and over. Now consider those progeny raised during extensive drought with no supplementary feeding. Those babies have to-die-for genotypes (as evidenced by their pedigrees), but those genes won’t manifest as to-die-for phenotypes. Those babies will probably grow to be stunted, malnourished adults underperforming in the traits they were bred for.
An example is medium wool sheep raised in harsh conditions so as to grow (force) a lower micron fleece than their genotype would otherwise code for. The animals are not at peak performance, and while the wool will be fine®, it will probably be brittle and susceptible to breakage when processed on high-speed industrial machinery. Compare this to genetically-fixed fine wool sheep consistently producing a low micron fibre of even diametre and strength in less harsh conditions.
E in the simple formula above is often taken to be physical environment. This includes availability of feed, feed quality, water quality, altitude, soil, and the weather and seasons.
But E includes more abstract factors which are also environmental (nongenetic) influences on phenotype. These are: fixed resources, management, and economics.
Fixed resources are such things as farm size, workable land and labour - can additional, more nutritional feed be grown to boost phenotypes for example?
Management is the farmer’s policies. Policies could include supplementary feeding, vaccinations and deworming to increase animal health, which in turn leads to more productive phenotypes. Or a breeder may introduce animals with better genotypes to his herd to improve future generations’ phenotypes.
Economics covers all farm inputs (costs) and outputs (prices for animals and their products). Feed, labour and husbandry inputs can all affect phenotypic outputs, which in turn influence prices obtained.
The goal of breeding is to improve phenotype by improving genotype, but there is more to this than simply cobbling together a pedigree with desirable ancestors. Remember that P = G + E, and neither G nor E can be taken in isolation on your quest for P nirvana. Rather, you need to consider an animal as part of a system, something we’ll go into more in the next post.