Posted by on 27 Feb 2018 in Background Information

Knowledge of Interactions and How This Can Influence Breeding Objectives

Good breeders will have a breeding objective—a goal to develop an animal that to them is the “best” of its kind for the traits they desire. What is “best” for one breeder may well differ to what is “best” for another, and even for the same breed. For example, breeders of working Border Collies place importance on how well their dogs can herd sheep, and not so much on how they look. A breeder of show quality and pet Border Collies would place more emphasis on how symmetrical and evenly marked their dogs are. The objectives are different, but neither is more right than the other—each is “best” for the end purpose.

Most breeders would be familiar with the effects of environment on genotype. In Australia, temperate cattle breeds are found in the temperate regions and tropical cattle breeds are found in the tropical regions as this is where they perform best.

Yet not as many would be as familiar with genotype by environment interactions, and not knowing this concept may be detrimental to an oherwise sound breeding plan.

Going back to brisket disease in the Examples of Genotype-Environment Interactions in Animals post: let’s suppose a US cattleman with superior beef cattle but unfamiliar with brisket disease (extremely unlikely, but just to make a point!) relocated his herd from a low altitude to a high one. The consequences could be fatal for his herd and economically disastrous for him if his animals prove susceptible to high arterial pulmonary pressure. If he had never moved he’d have never known, and his valuable genetics would not be lost, though he may have always wondered why Colorado cattlemen never bought his prize bulls. (The test that measures arterial pulmonary pressure is only accurate above 1,800 m (6,000 ft).)

Several examples of G × E interactions are described in this document.^[1] The example on p2 describes research done on two closed lines of Hereford, a temperate beef breed. One line had been developed in Florida and the other in Montana. Some years later, part of each line was transferred to the other location, and each line evaluated side by side. The graph on that page (Figure 3) shows a noticeable difference in weaning weight, as well as a reranking of the two lines at each location. The Florida-bred line (genotype), though the same breed as the Montana-bred line (genotype), had adapted to the tropical environment of Florida and performed more consistently across the two environments. It outperformed the Montana line in Florida, but the Montana-adapted line still outperformed the Florida line in Montana. The graph is a real-life version of our hypothetical temperate-tropical graph from the Examples of Genotype-Environment Interactions in Animals post.

This example illustrates the point that breeders may—depending on their requirements—better meet their breeding objectives by sourcing new genetics from proven animals in their local region, rather than sourcing proven animals from very different environments. Similarly, breeders may not expect to sell animals—depending on buyers’ requirements—to environments different to the one they were bred in, and—depending on the traits—expect them to perform as well.

It is well worth considering in any breeding programme the potential effects of genotype-environment interactions. Being aware of such interactions may shed light on previous animal performance mysteries and help reach a breeding objective more effectively.

Remember that G × E interactions graph at least two genotypes and at least two environments. If just one genotype shows a change in different environments, the graph would consist of a single line. This represents nothing more than a simple environmental effect on animal performance, though of course it is just as important to consider in breeding plans.

It’s worth mentioning here that there are other graphable interactions involving genotype: genotype by management and genotype by economics.

A genotype by management interaction may show the best age for slaughter in terms of carcase weight and fat distribution for example.

A genotype by economics interaction might be apparent when considering labour and/or capital costs. Milk production is more productive with high input and labour than the reverse for example.

Genotypic interactions can be quite involved, but having an indepth knowledge of them can be very revealing and insightful. Ultimately a breeder can come to know a lot about how The Animal is Part of a System, and how the industry itself is a system.

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