Written by: Ross Tellam, Ph.D. | Issue # 63 | 2017
- Dairy cattle obtain most of their protein nutritional requirements from feed that is inedible by humans.
- Intensive dairying uses additional feed supplements containing plant protein that is edible by humans.
- The ratio of human-edible protein produced in cow’s milk to human-edible protein ingested by the cow is proposed as an index of the sustainability of feed supplements in a future world with increasing competition for protein resources.
- Dairy cows currently produce more human-edible protein than they consume.
- Future assessments of sustainability will also need to take protein quality into account because the quality of milk protein is higher than plant protein for human nutrition.
Much More Food Required by 2050
An expert panel that contributed to a 2009 Food and Agriculture Organization of the United Nations (FAO) report entitled “How to Feed the World in 2050” calculated that world food production would need to increase 70% by 2050 to meet the challenge of feeding 9.7 billion people [1, 2]. For many of today’s agricultural scientists, this is a daunting, though some say achievable, number .
The 2009 FAO report indicated that although additional arable land in the world could become available for growing more crops for human consumption by 2050, this land will be limited in quantity and would likely support only a narrow range of agricultural species . The report concluded that food production and its utilization will need to become much more efficient. Inevitably there will be competition for resources between different agricultural industries and questions raised regarding the sustainability of some agricultural practices. There may be greater attention paid to the net benefit to humans of using human-edible plant protein in livestock feed supplements . The livestock industries need extensive protein-use efficiency data to enable future decisions on the optimum use of resources for plant and animal protein production.
Competition for Dietary Protein
The human demand for dietary animal protein is growing, not just as a result of population increase, but also because there is increased demand per individual within the more affluent and growing middle classes of many countries . Dairy products are rich sources of protein for human consumption. Another FAO report concluded that global milk production will need to increase by 58% by 2050 to meet demand . This will be a challenge for the dairy industry, although a similar percentage increase of milk yield in the USA was achieved over the last 30-40 years .
Grazing ruminants like cattle have the remarkable ability to transform pasture unsuitable for other agricultural purposes into energy- and protein-dense meat and milk suitable for human consumption. The cow’s dietary protein obtained from pasture is inedible by humans; however, intensive dairying now uses plant-based feed supplements containing human-edible protein to support the increasing demand . In a recent publication, Christian Swensson and colleagues from the Swedish University of Agricultural Sciences and five other Swedish institutions suggest that this practice will generate competition between the intensive dairy industry and humans for agricultural resources producing human-edible plant protein . Ultimately, the practice raises a question about the sustainability of intensive dairying in a much larger world population directly competing for human-edible protein.
The research group led by Christian Swensson investigated production data from intensive dairying occurring in five locations in Sweden, each with different types of feed supplements . The researchers calculated the ratio of human-edible protein produced in cow’s milk per unit of human-edible protein in the feed intake of the cow. A ratio larger than one is favorable for the dairy industry. The main conclusion was that five of the six tested regions had ratios greater than one, i.e., those regions contained cows that created more human-edible protein than they consumed. However, the investigators noted that higher milk yield tended to decrease this ratio regardless of diet. In biology, there are no free lunches.
The important progress made by the researchers was to distinguish between human-edible and human-inedible protein used in a variety animal feed supplements. The researchers also included data in their calculations relating to the digestibility of human-edible plant protein in the feed supplements. They also suggested a need for future adjustments in their calculations to compensate for the lower nutritional quality (to humans) of human-edible plant proteins in feed supplements compared with the quality of the milk protein output.
Plant and Animal Proteins Do Not Have the Same Nutritional Value
Scientists have reported in many investigations that plant and animal proteins are different in their nutritional value to humans [7-9]. Humans and livestock break down dietary protein into its twenty component amino acids in the intestinal tract. Animals then absorb the amino acids into their body where tissues use them to synthesize new proteins that contribute to all cellular structures and functions. For humans and cows, there are nine amino acids (essential amino acids) that they cannot synthesize in the body from other molecules and therefore must come from the diet. The amino acid composition of animal protein, like milk proteins, perfectly suits the protein nutritional needs of humans.
Plant proteins in dairy feed supplements often have low levels of some essential amino acids. Therefore, the quality of these plant proteins for animal nutrition, including human nutrition, may not be optimal. For example, feed supplements containing only soy protein are deficient in the essential amino acids methionine and lysine, grains are deficient in lysine and legumes are deficient in methionine and cysteine. Dairy producers often use combinations of plant feed supplements to partially compensate for these deficiencies.
Future assessments of the sustainability of using human-edible protein in dairy feed supplements will require consideration of protein nutritional quality in the protein efficiency calculations. These adjustments may show even greater advantages of using the dairy cow to efficiently create protein suitable for human nutrition from an optimum balance of pasture and feed supplements containing human-edible protein.
1. Food and Agricultural Organization of the United Nations. High level expert forum – how to feed the world in 2050 Rome, FAO: FAO; 2009 [Available from: http://www.fao.org/fileadmin/templates/wsfs/docs/expert_paper/How_to_Feed_the_World_in_2050.pdf.]
2. United Nations. World Population Prospects 2015 Revision United Nations, New York: United Nations; 2015 [Available from: https://esa.un.org/unpd/wpp/Publications/Files/Key_Findings_WPP_2015.pdf.]
3. Swensson C, Lindmark-Månsson H, Smedman A, Henriksson M, Modin Edman AK. Protein efficiency in intensive dairy production: A Swedish example. J Sci Food Agric. 2017.
4. Thornton PK. Livestock production: recent trends, future prospects. Philos Trans R Soc Lond B Biol Sci. 2010;365(1554):2853-67.
5. Food and Agricultural Organization of the United Nations. World livestock 2011 – livestock in food security FAO, Rome: FAO; 2011 [Available from: http://www.fao.org/docrep/014/i2373e/i2373e00.htm.]
6. USDA. USDA agricultural projections to 2022: USDA; 2013 [Available from: http://www.thecattlesite.com/reports/?id=1573.]
7. Boland M. Global food supply: the world’s need for protein New Zealand: Riddet Institute, Massey University, New Zealand; 2013 [Available from: http://www.riddet.ac.nz/sites/default/files/content/2013%20Protein%20supply%20Mike%20Boland.pdf.]
8. Ertl P, Knaus W, Zollitsch W. An approach to including protein quality when assessing the net contribution of livestock to human food supply. Animal. 2016;10(11):1883-9.
9. Food and Agricultural Organization (FAO). Dietary protein quality evaluation in human nutrition: report of an FAO expert consultation. Rome, Italy: FAO; 2013 [Available from: http://www.fao.org/ag/humannutrition/35978-02317b979a686a57aa4593304ffc17f06.pdf.]