Easy care sheep developed by AgResearch were produced using selective breeding. Find out more about selective breeding and why scientists use this method to breed the easy care traits.

Selective breeding: an ancient technique

Selective breeding is a process of selecting the traits you want and mating the animals with those traits together to produce more of the traits in the progeny.

Farmers have used selective breeding to improve the performance of their livestock since animals were first domesticated. Modern methods for breeding specific traits, such as genetic modification and cloning, have emerged since the discovery of DNA. Currently, such methods are only practised in research organisations in New Zealand but may be used in the future. Could modern methods be more effective than selective breeding for producing easy care sheep? New Zealand has many applications for modern biotechnologies, including transgenic cows that make modified milk or human therapeutic proteins in their milk.

Selecting the traits

Dr David Scobie and his team at AgResearch identified traits they considered desirable for an easy care sheep, such as a bare backside, bare belly, bare head and legs and short tail.

Some traits, such as bare heads and legs, are easily identifiable in common New Zealand breeds, others were discovered by reading the scientific literature on sheep. Some breeds carry many of the desired traits but none carry all of them.

Scientists found the bare belly the most difficult trait to locate because it’s not fixed in any particular breed – it occurs from time to time in a number of breeds. This means the genes are recessive. You can learn more about dominant and recessive genes in the useful links at the bottom of the page. The article Finding easy care sheep traits describes the processes that AgResearch went through to get sheep that were more productive and less labour-intensive for farmers.

Inheritance of traits

Each trait is controlled by 1 or more pairs of genes inherited from the parents. The combination of traits expressed by an individual sheep is known as the phenotype.

Read these articles to find out more Cell biology and genetics and Genes involved in footrot.

Heredity and the environment

 

There are significant differences in the traits between different breeds of sheep but there are also differences within breeds. These differences are referred to as variation. Variation is partly due to genes inherited from the parents and partly due to the influence of the environment the animal has grown up in. Different traits vary in how much heredity or the environment contribute to their occurrence or their heritability.

Measuring heritability

To determine the heritability of particular traits, scientists need to estimate what percentage is due to heredity and how much is due to environment. They calculate this by examining the extent to which related sheep resemble each other in a particular characteristic when they have been raised in the same environment.

Scientists record their observations and give each trait a heritability value between 0 and 1. They define the degree of heritability as:

  • less than 0.15 – low heritability
  • 0.15 to 0.3 – medium heritability
  • over 0.3 – high heritability.

These values provide a guide for farmers on heritability of traits – the higher the heritability, the more quickly a trait will be reproduced in subsequent generations. Traits with low heritability may take longer to identify and will therefore take longer to breed into a flock.

When only 1 trait is selected, progress in breeding that trait is much faster than dealing with multiple traits. Selecting more than 1 trait at once is complicated because some traits may be associated – this is referred to as genetic correlation.

Scientists estimate that it would take 5–7 years to breed all the easy care sheep traits into a full flock.

Commercialising the research

Although the scientists bred sheep with the easy care traits, their aim wasn’t to produce a new breed of sheep to sell. Their aim was to prove that it could be done, show the benefits and provide information to farmers on how to do it. It is up to farmers to choose whether to create these changes in their own flocks, to any breed of sheep, and be supported in the process.

The project was funded by Meat and Wool New Zealand Ltd and indirectly through research levies previously collected from farmers. The information is available free for farmers on the internet and is promoted through newspapers, magazines, radio, television and agricultural shows such as National Fieldays.

Whether or not farmers use the information and breed easy care traits into their flocks will depend on their perceptions of the economic and welfare benefits. Some may be influenced by their views of what particular sheep breeds should look like, or some may be wary of possible harmful effects in the long term.

Learn more about the discovery of heredity in the article Biology idea 2: The gene.

Useful link

Learn more about heredity and traits on Utah University’s Genetic Science Learning Centre website.

    Published 18 July 2010