How are Breeders Helping to Reduce Emissions?

朱春明

Past genetic improvements have significantly contributed to a reduction in the emission of greenhouse gases (GHG) per unit of animal product, and breeding remains an important tool in further reductions. These key points were made by Dr Huw Jones of Genesis Faraday at the most recent JSR Genetics Technical Conference, reports Jackie Linden for ThePigSite. "Livestock production accounts for 18 per cent of world's GHG emission in carbon dioxide (CO2) equivalents. That is is higher share than transport," said Dr Jones, quoting from a 2006 report of the Food and Agriculture Organization (FAO).

Dr Huw Jones

One significant aspect lying behind the statement is that ruminants present the greatest environmental burdens, although the pressure for GHG reduction also applies to pigs and poultry. Furthermore, the global demand for meat and animal products is increasing, so simply reducing consumption in developed countries will not substantially reduce the global impact of animal production.

Most importantly, changes must and can be made to reduce the amount of GHG emissions per unit of product, emphasised Dr Jones. He added that possible options include changes in management, e.g. farms, manure, animals, feeding and genetics.

Some important progress has been made in recent years. A leading example is a UK study by Cranfield University and Defra, which modelled the effect of genetic improvements on emissions from commercial livestock operations of methane (CH4), ammonia (NH3) and nitrous oxide (N2O) per unit of product over the last 20 years and for the next 15 years. As a basis, they used a lifecycle assessment model (Figure 1).

Figure 1. Life cycle assessment model

Among a series of sub-models, they considered the full life cycle of all animals considered, as well as the industry structure and production systems typical of the UK at that time (2007). For pigs, this represented 80 per cent of breeding herds outdoors, 25 per cent of weaners outdoors, market weight breakdown (70 per cent at light weight, 20 per cent at medium weight) and 0.6 per cent organic production. For eggs prodction, this represented the following systems: cage, 64 per cent: barns, 6 per cent; free-range, 28 per cent) and organic, 2 per cent.

Using 2007 as a base, the model predicted performance back to 1988 and forward to 2022 using genetic trends, under constant management conditions.

The UK's industry input covered 2007 production levels for different commercial systems, rates of genetic improvement achieved in purebreds over the previous 15-20 years, and the uptake rate of the improved genetics at the commercial level. For example, at the commercial level, the annual rates of genetic change in pigs were 6.4 g in lifetime daily gain, a fall in feed conversion ratio of 0.02 and an extra 0.12 piglets born alive per litter. For poultry, the annual rates of genetic change at the commercial level were increases of 0.8 g in daily weight gain and 0.1 per cent in killing-out percentage, reductions of 0.02 in feed conversion and 0.07 per cent in mortality and an extra 0.9 eggs per breeder hen.

This data led to the calculation of emissions of CH4, NH4, N2O and GWP 100, a measure of overall emissions (Table 1). From this, the percentage of this changes brought about by genetic improvements were calculated (Table 2.)

Table 1. Emissions (kg) per tonne of product (2007)
	Methane CH4	Ammonia NH3	Nitrous Oxide, N2O	GWP 100
Layers	7.5	28.0	3.8	3791
Broilers	4.9	23.0	3.4	3448
Pigs	48.8	27.8	2.3	4689
Dairy	18.9	3.4	0.6	958
Beef	264.5	71.4	11.6	14704
Sheep	300.9	41.3	11.3	15813

Table 2. Percentage changes through genetic improvement (1988-2007)
	Methane CH4	Ammonia NH3	Nitrous Oxide, N2O	GWP 100
Layers	-30	-36	-29	-25
Broilers	-20	10	-23	-23
Pigs	-17	-18	-14	-15
Dairy	-25	-17	-30	-16
Beef	0	0	0	0
Sheep	-1	0	0	-1

The annual percentage reductions in GWP for the period 1988-2007 were: layers, 1.3; broilers, 1.2; pigs and dairy, 0.8. For beef and sheep, there was no change.

Further analysis allowed the researchers to determine where the observed benefit in the pig and poultry sectors had been derived. Figure 2 shows how each of the genetic immprovements in performance of pigs has impacted the emissions of the GHGs studied. Figure 3 shows the same analysis for broilers.

Figure 2. Genetic improvements related to GHG reductions in pigs (1988-2007)

Figure 3. Genetic improvements related to GHG reductions in broilers (1988-2007)

Dr Jones asked what would happen if all male cattle and sheep we recorded, and their rates of genetic gain were the same as for the current best farming animals. For cattle, this would bring an annual improvement of 0.3 per cent., or 4.4 per cent in 2022 compared to 2007. For sheep, the improvements would be even greater - at 0.54 and 8.1 per cent, respectively.

So while there is potential to reduce GHG emissions from cattle and sheep, what more can be done to further improve the situation for pigs? Dr Jones offered six possible strategies:

• use new tools to accelerate the rate of improvement
• focus selection on new traits, such as disease resistance
• optimise production systems, matching genetics to specific systems
• develop comprehensive models to allow the benefits of different options to be assessed.
• further research to investigate whether there is genetic variation in the efficiency of digestion or the absorption of nutrients, and
• directly considering GHG emissions among the selection indices.

"Past genetic improvements have already helped reduce emissions per unit of product substantially," said Dr Jones, and he added that these results are likely to be an underestimate of the improvements, especially for pigs. The good news is that these rates of improvement are likely to be maintained as long as current selection practices continue, and new technologies and/or new traits may deliver even greater gains. He emphasised that it is important to ensure that breeding is recognised as an important tool for reducing emission from livestock production.

As a final conclusion, Dr Jones said, "The results of the study are very promising, and provide a valuable platform on which to build for the future."

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孟俊英

謝謝分享，育種工作是減少家畜生產(chǎn)中溫室氣體排放量的重要一環(huán)，這一領(lǐng)域前景廣闊，值得有為青年為之奮斗