4 February 2009

7 minute read

DNA can be read like a book
Image: StockXchng

Reading DNA is like deciphering an ancient language. When genomes were first mapped it was believed that each gene described a single trait. Now, it is understood that many genes can affect a single trait and scientists are getting closer to understanding how they really work. Many traits can already be altered through genetic selection, creating livestock that suits the farmer's needs.

"Selection works", says Professor Geoff Simm of Sustainable Livestock Systems Research Group, SAC. According to him there is a wide-range of real evidence, including livestock experiments , breeding schemes and lab animal studies that show that selective breeding is an effective tool in improving livestock efficiency. Speaking at the 2009 Quality Meat Scotland Research and Development Conference in Perth, Scotland, he said that most traits can be altered by selection and those those that are continue to give a response over many generations.

But what rates of genetic change can be expected in livestock farms? It all depends on which animal is targeted, says Prof. Simm. Higher rates can be achieved when genetic variability is high and the trait is not limited by age or sex. If a species has a high reproductive rate then the genetic change can be expected to show itself much sooner.

This is one of the reasons why lab rats are used so often in genetic tests. Because the rodent breeds quickly, with short pregnancy times and large litters the opportunity to see and respond to genetic change happens at a much greater frequency. In essence these animals speed up this process of artificial evolution by shortening the age between one generation and the next.

For this reason, rates of livestock change happen faster for pigs and poultry than they do for sheep and beef cattle, similarly on a commercial level, the rates of change are greater and therefore initially more valuable.

Currently, cumulative rates for genetic change in beef cattle stand at just under 1.5 per cent per annum. These results are reflected in the milk, fat and protein weight changes and can be traced back ever since genetic breeding began. In particular, milk yields indicate a huge difference for dairy cows. Whereas the average dairy cow in the 1920's American farm produced a milk yield of roughly 2000 litres, modern day US cows produce 8,000 litres. However, it has been reported that this increased milk yield has been accompanied by declining ability to reproduce, increasing the incidence of health problems, and declining longevity in modern dairy cows.

European pig breeding programmes have also witnessed notable changes of late. Litter size has increased by a yearly average of 0.2 pigs per litter and daily LG gain stands at around 2.4 per cent, an increase of 20 g/d. Genetic changes in broilers have had even more noticeable changes. Just by looking at photographs documenting the change in carcass size throughout the years shows evident weight gains. To put this into figures Prof. Simm compared an average broiler from 1976, to one from 1999. In 1976 the liveweight of a broiler after 42 days was 1050 grammes, but by 1999 this number had increased almost 250 per cent to 2,600 grammes. It took 63 days for the broiler from 1976 to reach 2kg in weight, but by 1999 it took only 36.

Prof. Simm summed it up: "This change is either a miracle of biology, or an obesity depending on what camp you're in". Breeding organizations are concerned with what type of animals will populate their farms in the future and how they resemble the animals that we see today, and in turn, generations ago. But, however people think about it, there is no doubt that genetic variation is a major player in todays world of livestock farming and will continue to be so for years to come.

Many producers today question the value of genetic variation to their operations. Recent studies - conducted by SAC and partners - analysed the farmgate value over 10 years of genetical selection. "The outcome was determined using actual breed numbers, genetic trends and realistic estimates of costs and returns", says Prof. Simm.

Throughout Scottish farms it was estimated that the sheep industry benefited from genetic variation to the tune of £29 million. However, the research indicated that with a higher uptake across the industry this figure could have stood closer to £111 million. Similarly, over the same period of time, the beef industry benefited by £23 million. Rather than uptake, the main improvement here would be a more effective terminal sire versus maternal selection. The internal rate of return on investment for the sheep and beef industry was 32 per cent. Benefits increased by double when accounting for lower interest rates.

Trying to come to terms with why more producers are not jumping on the genetic bandwagon, Prof. Simm alludes to potential structural blockages. Small flock/herd sizes may not warrant the effort, whereas different systems and environments also make it difficult to adapt these changes into a producers programme. Some farmers may be put off by market failures because returns for their product often don't value the 'improvements' made.

The success of these industries depends upon public perception of its products and production methods and increased public concerns regarding modern animal agriculture, particularly animal welfare. Prof. Simm also points out that there may be underlying reasons of tradition, beauty and fashion that stop farmers from making the move.

But there are other benefits to genetic improvement says Prof. Simm, more than just yielding a higher value product for less. Whilst consumers consistently spend less of their GDP on food and non alcoholic drink by ratio a market may open up for it. He also says that this process can help produce leaner, healthier meat. Although much of the public has come to accept the possibility of this research, the latest claims based on welfare friendly and environment claims sit less comfortably.

Prof. Simm asserts that genetic improvement may alleviate flaws and defects that currently cause stress and pain to the animals afflicted. Furthermore, greater research may soon overcome some of the more common diseases that can be disastrous for both animals and farmers. However, the changes that many producers search for in their livestock often bring about physical change that can put unnatural stress on their animals bodies and in doing so cause mental stress as well.

Further research is clearly needed to clarify the relationship between production, negative energy balance, metabolic stress and welfare indicators, whilst practical methods to measure these factors are needed in order to enhance selection tools used to improve welfare status in livestock.

The claim to environmental benefits stems from an ability to lower the green house gas emissions of livestock per unit of product. This can be achieved by genetically altering the animals digestive systems to produce less waste and also by improving the efficiency of weight gain by comparison with input. If an animal reaches its optimum size in a shorter amount of time then more meat or milk can be produced on the same plot of land.

Prof. Simm points out that in a world where 30 per cent of ice-free land is devoted to agriculture - and of that 70 per cent of it is used for livestock production - how efficiently producers can raise their livestock is of emerging importance. With the consumption of meat expected to double in the fifty years between 2000 and 2050, the efficiency of food production as a whole will no doubt become a much greater issue worldwide.

Prof. Simm says that this is especially serious given climate change issues, but makes it clear that livestock isn't merely a problem, "it needs to be considered as part of the solution". Although ruminants have the greatest global warming potential of all livestock animals, they also have the amazing ability to produce meat from an inedible resource; grass. It is abilities like this that will need to be exploited in the future.

The age of genetic selection may have come, but it has not yet been embraced by the whole farming community. Prof. Simm says that it has a lot more to offer than what we have seen so far. He outlines the new opportunities: the sustainable breeding goals addressing both global and local priorities; the new data and the new measurements; he illustrates the ability of video based grading and CT scanning to accurately evaluate the "superior" meat quality and talks about the molecular genetic tools in production that will help to bring about a "biological revolution".

There are still many blocks to genetic research, but Prof. Simm says that he will try and sell his message through the education system and focus on areas where it has already achieved success. He says that a lot of the problems boil down to a "generation thing". Yet, despite of all the opportunities that genetic selection there is something unnatural about it that still discourages farmers. Perhaps it is something to do with the tradition of farming with animals that Prof. Simm mentioned, something beautiful in the natural production methods that prevents the biological revolution from dominating the livestock world.

February 2009