The role of pig genetics in global sustainability and responsibility
The pig industry has achieved a lot in reducing its climatic impact, and further improvements lie ahead.
Over the last decade there has been increasing interest in environmental issues, such as climate change and sustainability. A key player has been the Inter-governmental Panel on Climate Change, IPPC, set up to assess technical, scientific and sociological impacts, including the role of agriculture in global warming.
Agriculture has been largely successful in feeding the world, but the global population is growing. The Food and Agricultural Organisation, FAO, has estimated that, to meet demand growth from 2000 to 2030, cereal production must increase by 50% and livestock production by 85%.
The sustainability debate was galvanised by the 2006 publication of the Stern Review on ‘The Economics of Climate Change’. It indicated that agriculture was responsible for 14% of global greenhouse gas emissions, GHGs, in 2000. The Australian Garnaut Review reported that this had increased to 15% by 2008.
Pig environmental studies
There are several studies on the impact of pigs on the environment. For example, Danske slagterier reported in 2008 that between 1985 and 2008, there were highly significant reductions in chemical discharges from pig production: 39% less nitrogen; 42% less phosphorus; and 50% less ammonia.
Additionally, there was a 50% reduction in use of artificial fertiliser on arable land, due to increased use of pig slurry. Overall, it was estimated that GHG emissions per kg of pig meat had fallen by 17% in the16 years since 1992.
Another Danish report considered changes in eutrophication, acidification and global warming/GHG. It showed highly significant projected falls from 1995 to 2015 of 74% in eutrophication, 50% in acidification and 25% in GHGs.
Influence of genetics
Plastow has reported that 40 years of genetic progress have halved the manure produced on a per productive sow basis, and that the land needed to produce a cooked breakfast of eggs and bacon has been reduced by 70% through improved efficiency. Perhaps, of greater importance has been genetic progress across a range of performance and efficiency traits. Van der Steen, Prall and Plastow showed in 2005 significant phenotypic changes from the 1960s, which had a sizeable genetic component.
Walling (2008) noted that the best performing units now far exceed the average benefits, so that the percentage change from the 1960s in pigs weaned per litter is over 100% and more than 200 kg of lean per tonne of feed is seen on the most efficient units.
Despite the positive trends in genetic progress, little has been published on the correlated benefits for the environment. However, Audsley, Jones and Williams (2007) reported on modeling work at Cranfield University which looked at the effect of improved genetics in livestock on GHGs using an input:output life cycle model. Table 2 shows the differences between livestock in emissions.
Comparing the 20 year period 1988-2007, the authors reported significant percentage falls in methane, ammonia, nitrous oxide and GWP in pigs and poultry but not in beef and sheep.
Based on these data, the authors concluded that the annual reduction in GWP in pigs through genetic improvement was 0.8% over the last 20 years. They also forecast that, if the same levels of genetic progress were achieved over the following 15 years, then there would be further reductions in methane, ammonia and GWP of 15%, 14% and 14%, respectively.
Genetics will continue to play a key role in ensuring global sustainability. The main advantages of genetics are that gains are cumulative and permanent. Furthermore, most genetic techniques are ‘sustainable’. Essentially, there are five main routes through which genetic improvement can help to reduce GHG emissions.
Improved productivity and efficiency
As shown above, selection to date has been impressive. Among benefits from selection are higher gross efficiency by reducing the overall maintenance cost of production, a requirement for fewer animals and a reduced finishing period, directly lowering emissions and slurry produced.
Among particular challenges that may become more important are:
a) Reduced feed intake. Reducing intake is a feature of many breeding programmes. The result is that genetic potential in lean growth is increasingly restricted.
b) Heat stress. Increasing levels of heat stress are likely to occur as global temperatures rise. As a result, appetite will be reduced in order to reduce heat production. There is some evidence that heat stress related problems are emphasised in ‘modern’ lines with high levels of lean growth and reproductive potential, so that genetic selection might be used to improve resistance to heat stress.
c) Daily maintenance yields. Selection for lean growth has led to animals of larger mature size with higher maintenance needs. This has implications for breeding programmes faced with the need for increased efficiency and minimization of GHGs.
d) Exploiting nutritional differences between genotypes. Several studies have shown that there is genetic and individual variation in digestibility and post absorption for energy, fibre and protein.
Selection for fitness traits will reduce wastage levels. Most of the traits are complex, but the underlying genetic components/genes are being unravelled.
One aspect of climate change is that higher global temperatures will result in greater disease burdens. Already the costs of disease are huge, so it is hoped that technologies will develop that allow disease resistance to be exploited.
Direct selection to reduce emissions
In the ruminant it is known that there is variation between animals, between breeds and across time for the production of GHGs. However, direct measurement in live animals is difficult, so selection for decreased GHGs must remain a goal. However, in the pig there is the example of the ‘Enviro Pigs’, which have been genetically-modified to excrete 60% less phosphorus.
Developing new indices for selection on emissions
As the environment changes, it is possible to invest in broader breeding goals. These breeding goals can be built in a number of ways, but the ‘valuation’ of traits may be complex as there are several scientific approaches. These include the use of restricted or desired gains, the use of relative economic values, the adaptation of economic values based on ‘conjoint’ analysis and total farm modeling, where trait changes are related to environmental impact.
Exploiting genetic resources
There is growing awareness of the potential long-term importance of domestic animal genetic resources. One of the reasons for maintaining these resources is that a ‘pool’ of genes and gene combinations will be available for the future, acting as insurance if ‘modern’ genotypes fail in a particular environment or have low gene frequencies in a desired trait. There are several examples of favourable gene frequencies in ‘traditional’ breeds – for example the K88 E. coli resistant gene was found at high frequencies in several non-commercial genotypes.
Many of the genetic techniques will require high levels of expenditure to allow their successful development. At a time of global uncertainty about funding levels for research it is important that the case for genetics funding is made forcibly.