Thursday, 21 February 2013

Defining breeding targets and trait values

An animal breeding is not just about calculating breeding values and creating statistics. It starts with a difficult task: defining what "best animals" are like, and what to measure. Only that which is measured can also be improved.Good breeding goals are
  • well defined
  • reliable, easy and cheap to measure and record
  • aim to the future (help the animals adapt to the coming changes.
Goals can also be ethical, political or biological, and either global, national or areal. For example, national policy may dictate that local breeds are to be conserved, which prevents cross-breeding. Biological goal could be the need to improve fertility, and ethical goals such as breeding only healthy animals is (or should be) a global target. Also,  breeding can only target traits which have genetic variation. If every animal already has long horns, it's not feasible to aim at short horns.

Once a list of breeding goals has been made, the goals need to be weighed. Every goal cannot be the most important. Factors influencing the weighing process are
  • defining efficiency: biological and economical views
  • target of selection: maximizing profit or minimizing costs
  • production system: developing animals / herds / breeds
  • limiting factors: Limiting production inputs, number of animals
  • range of planning: what needs to be inmproved first, and what later
  • different roles in the food production chain: slaughterhouses have different goals than piggeries or animal welfare professionals
Example: values of fertility and udder health
 Animal breeding for farm animals targets mostly at better income for the farmer. Each trait can be given an economic value based on how it increases profits or decreases costs. Better fertility decreases medical costs, while inreased milk/meat yield increases profits and decreases cost of milk liter/cow.. A profit function has been defined to describe changes in net profit as a function of modifiable parameters (physical, biological and economical). For breeding to be profitable, the changes leading to better revenues must be caused by genetic improvement. But focus on profits has its downside. Animals are culled as soon as their production decreases, even if their best production seasons would still be ahead. Increased production is a heavy stress on metabolism and health, causing a variety of ailments on the animals.

Costs of traits for pigs have been valued to show how much an improvement of one unit of standard deviantion increases the price of pig meat. In one study, the most profitable trait was the size of litterm which increased the price of pig meat  2 cents / kg. The least profitable traits was the size of the first litter. Some breeding programmes like the Northern European NAV has defined clear values for different traits, as can be seen in the picture below.

Values of traits in NAV. (c)

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