Livestock breeding and sustainability
Professor Geoff Simm
Science for Sustainable Agriculture
Genetic improvement of farm livestock productivity is a key factor in ensuring the availability and affordability of highly nutritious food, increased food security, and improved resource-use efficiency. Improved scientific understanding in recent decades is supporting more sustainable breeding programmes that better balance the emphasis on productivity and animal health and welfare, that address environmental impacts, and promote sustainable use of farm animal genetic resources, writes Professor Geoff Simm, Director of the Global Academy of Agriculture and Food Systems at the University of Edinburgh.
The fortunes of the human race have been closely intertwined with animal husbandry since we first domesticated livestock around 10,000 years ago. Consciously or not, over that time we have selected for animal characteristics that best suit our needs – for food, fibre, transport, draught power etc. Increasingly sophisticated methods have been used over the last 70 years, especially in poultry, pig and dairy cattle breeding, and particularly in richer countries.
Effective genetic improvement programmes have achieved cumulative annual rates of change typically of 1 to 3% in traits of economic importance. These changes look small on an annual basis but, as they are cumulative with ongoing selection, the changes can be dramatic over a few decades. For example, much of the over 4-fold increase in the average yield of dairy cows in the UK since the 1930s is down to selection between and within dairy breeds.
Some applications of genetics that have focussed too narrowly on production or efficiency have had a negative impact on animal health and welfare. So too, a drive towards specialisation of breeds has led to erosion of genetic resources globally. Improved scientific understanding over the last few decades is allowing the design of more sustainable breeding programmes that better balance the emphasis on productivity and animal health and welfare, that address environmental impacts, and promote sustainable use of farm animal genetic resources. A recent international review of dairy cattle breeding programmes, for example, showed that the emphasis in selection has changed from being focussed almost exclusively on milk production a century ago to now placing around half of the selection emphasis on traits other than milk production, including health and functionality. This trend towards more balanced breeding goals is growing in most farmed species.
Changes in livestock performance generally lead to reductions in feed and other resources used per kg of product, and hence in greenhouse gas (GHG) per kg product too (GHG emission intensity). For instance, a comparison of US dairy systems in 1944 and 2007 estimated that modern systems required 21% of the animals, 23% of the feedstuffs, 35% of the water, and only 10% of the land per billion kg of milk produced. The 2007 systems produced 24% of the manure, 43% of methane, and 56% of the nitrous oxide per billion kg of milk compared with 1944 systems. Similarly, selection of chickens bred for meat production is estimated to have reduced feed required per kg of weight by around 35% over 25 years, with corresponding savings in land use and GHG emissions per unit of product.
Over the last 12 years or so, genomic selection has begun to revolutionise livestock breeding. Genomic selection involves selection of breeding animals based on the use of genome-wide genetic markers to identify individuals and families carrying markers known from previous studies to be associated with traits of interest. Genomic selection can allow earlier identification of elite breeding stock, and also allow selection for traits that are difficult or expensive to measure in commercial herds or flocks – like feed intake, methane emissions or disease resistance – once markers have been identified that are associated with these traits. Genomic selection is superseding progeny testing in the dairy sectors of most industrialised countries, as it allows earlier and more accurate estimation of genetic merit of bulls. Likewise, it is becoming widely used in pig and poultry breeding and in some beef and sheep programmes, with benefits in accuracy and the range of traits targeted.
While there are indirect improvements in GHG emission intensity from selection for productivity, there is growing interest in developing breeding programmes to directly target methane emissions. There is good evidence of heritable variation in methane emissions in cattle and sheep. However, there are complexities in measurement at scale, and potential unintended consequences of selection unless relationships with other traits of interest are understood and accounted for.
Research from the Netherlands has predicted that ongoing selection on the current NL national dairy breeding index will lead to a 13% reduction in methane produce per kg of milk by 2050, without direct measurements of methane emissions. However, by adding direct measurement of cow methane emissions and putting greater emphasis on reducing methane, reductions of up to 29% could be achieved by 2050.
Recent research in Edinburgh has identified microbial genes with significant impact on methane emissions. ‘Rumen microbiome-driven breeding’ using genomic selection based on the abundance of these microbial genes could lead to a reduction of up to 6% per annum in methane emissions. Work is in progress to further develop and test this approach, and importantly to explore relationships with other traits of interest.
Genetic improvement of productivity of farm livestock in many countries over the past few decades has helped to increase the availability and affordability of highly nutritious food, increased food security, and improved resource-use efficiency. Achieving sustainable food production globally requires moderation of animal-sourced food consumption in higher-consuming countries. However, improved knowledge about the design of sustainable breeding programmes, and new breeding tools, will continue to contribute significantly to food security and sustainability too.
Geoff Simm is Chair of Global Agriculture and Food Security and Director of the Global Academy of Agriculture and Food Systems at the University of Edinburgh.
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