CIEL | Why Protein Quality Matters in Livestock Production 2023

Why Protein Quality Matters in Livestock Production

Protein quality is not just about the nutritional needs of livestock, it is also about the nutritional needs of humans, which evolution has also shaped over time from early hunter-gatherers to our modern agricultural society today.

Combined with livestock’s ability to convert lower-quality feed into highly-nutritious, protein-based food, it is easy to see why farming evolved and why livestock play a key role in our food system. The modelling of different food production systems shows that the most efficient systems always have livestock playing a key role in this ‘up-cycling’ of food by-products and plant material that humans gain little nutritive value from. The common thread in these ideas is protein quality.

CIEL has commissioned the new report ‘Why Protein Quality Matters in Livestock Production’ to inform wider industry on the key issues to be aware of relating to how livestock nutrition is critically important to producing high quality food products, delivering farm profit and making efficient use of feed resources while reducing the carbon footprint of livestock food products.

CIEL has produced another relevant report focusing on the importance of nitrogen cycling which is available here. Given that proteins differ from carbohydrates and lipids due to their nitrogen content, that report is highly complementary to this protein report. We recommend you read that as well in order to gain a wider appreciation of nitrogen, protein and efficient production of highly nutritious food, in the context of net zero and livestock.

The report ‘Why Protein Quality Matters in Livestock Production’, published in November 2023, was accompanied by a special launch webinar where we were joined by report authors Dr Marwa Hussein and Lorna Shaw from SRUC who presented key report findings and answered questions from the audience.

If you have a particular interest in future events and initiatives CIEL is planning around this topic area, please indicate this on the contact form and we’ll be in touch to discuss further.

Report now available –

Why Protein Quality in Livestock Production

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    In recent years CIEL has produced several reports related to Net Zero and Livestock.

    A common theme has been the value livestock add to our food system by supplying higher quality protein than other food sources. This report focuses on protein quality because it is fundamentally important to the use of feed resources for efficient livestock production as well as to human nutrition. Not all proteins are equal.

    Protein from most plants are of a lower quality than from animals, but even the best plant proteins are not as high-quality as animal protein. Despite this, modern science has led to plant proteins being used very effectively in livestock nutrition using good diet formulation, quality ingredients and supplementation with synthetic amino acids. This report explains how that occurs. Proteins are unique in that they contain a high proportion of nitrogen in their molecular structure compared to carbohydrates and lipids (fats and oils). When proteins are not used efficiently by livestock, nitrogen losses increase, leading to negative impacts for our climate, air and water through emissions of nitrous oxide (a potent greenhouse gas), ammonia (a pollutant and respiratory irritant) or nitrate leaching (which has adverse effects in waterways).

    Protein quality directly impacts on this efficiency, with lower-quality protein diets leading to greater losses than high-quality protein diets.
    Livestock fall into two main categories for protein nutrition: monogastrics and ruminants. Nature has adapted these two animal types for different feed types, and this has an impact on protein nutrition and nutritional efficiency. There is not much difference in protein composition of products from these two types of livestock, but there is a considerable difference in how they obtain the protein they need from the feeds that evolution adapted them to.

    We look at these differences in this report and consider the consequence of the roles they can play in our food system.

    Protein quality is not just about the nutritional needs of livestock, it is also about the nutritional needs of humans, which evolution has also shaped over time from early hunter-gatherers to our modern agricultural society today.

    As omnivores, our digestive systems are optimised for diets containing both plant and animal products, meaning that the quality of animal protein is a close match to our needs. Combined with livestock’s ability to convert lower-quality feed into highly-nutritious, protein-based food, it is easy to see why farming evolved and why livestock play a key role in our food system.

    In fact, modelling of different food production systems shows that the most efficient systems always have livestock playing a key role in this ‘up-cycling’ of food by-products and plant material that humans gain little nutritive value from. The common thread in these ideas is protein quality. I hope you will gain a better understanding of this property of feeds and foods from our report.

    It is a critical component within the context of sustainable farming systems that requires a deeper runderstanding, particularly when exploring the potential role livestock should play in such systems.
    CIEL has produced another relevant report focusing on the importance of nitrogen cycling which is available here. Given that proteins differ from carbohydrates and lipids due to their nitrogen content, that report is highly complementary to this protein report. We recommend you read that as well in order to gain a wider appreciation of nitrogen, protein and efficient production of highly nutritious food, in the context of net zero and livestock.

    CIEL commissioned leading experts to produce this report in a style accessible to non-experts who have an interest in nutrition and food production. We welcome feedback and queries about concepts and ideas detailed in the report.

    The human population is rising which increases demand for high-quality protein. Increased affluence is also expanding demand for animal protein food products.

    This has placed demands on the production of meat, milk and eggs where previously diets have been based on plant proteins supplemented with a smaller amount of animal proteins. Protein quality is primarily related to the concentrations of different amino acids the protein contains and how available they are to the animal. Amino acids are the building blocks of protein and the closer the concentrations of the different amino acids match animal requirements the higher the quality of protein produced. A shortage of one amino acid will result in reduced protein synthesis and the wastage of the surplus amino acids. Of the 20 amino acids needed to make animal protein, around 10 are essential because they cannot be synthesised by the animal and must be supplied in the diet. For human nutrition, in terms of their amino acid content, milk and eggs are close to the ideal protein for humans and are considered of high-quality1 in the diet. Meat also contains a good balance of amino acids compared to plant proteins, which are also more variable in quality. Demand for animal protein is increasing rapidly, especially for poultry meat, putting pressure on sources of feed ingredients such as soyabean meal, currently the main protein source in poultry feed2,3. There are large variations in the amount of protein eaten and in sources of dietary protein consumed by humans. Generally, humans need to consume both animal and plant-based proteins to ensure that the quality of the protein consumed meets their nutritional requirements.

    To produce protein-based foods, animals must be fed a diet that meets their amino acid requirement for body maintenance processes and production of eggs, milk or muscle (protein) growth. Insufficient essential amino acids in the diet limits use of other amino acids for such processes. Excesses of other amino acids are used as an energy source which does not use nitrogen, leading to nitrogen being excreted.

    Nitrogen is excreted as urea, which is readily converted to ammonia (a pollutant and respiratory irritant), nitrous oxide (a potent greenhouse gas) or nitrate (plant growth promotant) that when lost through leaching adversely affects aquatic ecosystems. Optimising protein quality improves efficiency of protein use in the diet and helps to reduce harmful emissions. For monogastric animals (including humans) the dietary protein must supply all the amino acids the animal requires.

    Ruminant protein nutrition is different because micro-organisms in the rumen enable the ruminant to synthesise some of the amino acids they require. To do this, the microbes need to be supplied with a readily-fermentable energy source and either low-quality protein or nitrogen in a form they can use to make amino acids. Most protein
    used by ruminants themselves is microbial protein. Microbes are present in the rumen, which is the first stomach. Therefore, microbes are exposed to ingested protein before the animal can absorb this protein from the diet further down the gastrointestinal tract. To supply more protein to high-producing ruminants (e.g. high-yielding dairy cows), diets need to be supplemented with high-quality, undegradable protein which bypasses rumen degradation.

    Protein requirements change according to an animal’s physiological state (egg production, pregnancy, lactation, age and health) of the animal, increasing during pregnancy and early lactation, during the finishing stages of growth for meat production and during periods of illness. Diets can be fine-tuned to better meet requirements during these situations.

    To maximise protein synthesis, nutritionists must make the best use of dietary plant proteins, while minimising wastage of amino acids as currently all proteins used in UK livestock feed are plant based. These are an excellent source of amino acids, but their concentrations do not match animal requirements. To meet animal requirements diets are formulated predominately using soya and smaller amounts of other plant proteins. Essential amino acids (synthesised by industrial processes) can be added to improve amino acid balance. This results in a reduction in the total amount of protein in the feed for the same level of performance i.e. total protein content of the diet can be reduced but still meet protein requirements of the animal. This includes humans consuming a vegetarian diet where care must be taken to ensure a good balance of amino acids is consumed for optimum health. For ruminants when demand for protein is high, protecting amino acids or feeding high-quality undegradable protein sources enables high-quality protein to bypass microbial fermentation and be absorbed by the animal.

    Through accurate diet formulation and reducing the amount of feed protein in diets by supplementing with synthetic amino acid or protected amino acids, nutritionists can create feeds that meet requirements while decreasing demand for soybean and helping to reduce the overall carbon footprint for a production system. Further to reducing soybean meal in animal feed, we need to continue to look for alternatives to soyabean meal and consider how we might reintroduce animal proteins as an option for livestock diets, in particular monogastric animals.

    These concepts also impact farm profitability and the environmental footprint of agriculture. Animals, including humans, obtain energy from carbohydrates, lipids and protein, and have specific requirements for amino acids to make their own protein. The amino acid content of the feed protein compared to the balance an animal requires denotes the ‘protein quality’. Protein is more expensive than energy across feed ingredients and so protein nutrition is critically important to profitability as well as productivity of livestock systems. Animal products such as milk and eggs are ideal proteins for human nutrition because they contain significant quantities of amino acids in the proportions required. Protein from meat also has higher protein quality compared to plant protein which varies because of species and variety.

    Meat, eggs and milk also provide a variety of other important nutrients, in addition to high-quality protein. For livestock, as in all biology, there are natural inefficiencies in the feeding and use of protein that cannot be overcome. However, protein will be most efficiently used by animals when energy and protein, with the correct blend of essential and non-essential amino acids, meet the requirements of the animal. This also minimises nitrogen excretion from breakdown of amino acids in the gut which lead to production of ammonia (a respiratory irritant for animals and humans), nitrous oxide (a potent greenhouse gas), and nitrate losses to the environment.

    With low-protein quality diets more total protein is required to meet the needs of the animal. However, this is less profitable, less efficient and has a higher environmental footprint because metabolism of excess amino acids increases nitrogen losses which impacts on the environment. The goal should be to minimise the quantity of protein fed, while still supplying quantities and proportions of amino acids needed by the animal.

    Monogastric livestock can produce substantial amounts of protein extremely efficiently from cereals and protein crops, supplemented with essential amino acids and other nutrients, resulting in high-quality protein foods. Artificially produced amino acids and accurate diet formulation are key to maximising production and minimising emissions from poultry and pigs. Ruminant livestock have a unique relationship with microbes which affects their protein nutrition. Rumen microbes use the feed before the ruminant itself does and can modify the quality and quantity of nutrients that the host animal itself then digests and absorbs. This allows low-quality feed to be ‘up-cycled’ but also high-quality feed can be ‘down-cycled’.

    Ruminants are ideally suited to make use of lowquality roughage to produce high-quality protein foods. High-quality proteins will be ‘down-cycled’ unless protected from digestion by rumen microbes. While it is more difficult to precisely control protein nutrition in ruminants than in pigs or poultry, ruminants have adapted so they can use feedstocks that other animals and humans cannot. Thus, ruminants play a key role in human food production by converting fibre-rich plants (indigestible in monogastrics, including humans) and plant protein into highly nutritious foods.

    We face challenges in delivering more sustainable food systems for the future especially regarding protein supply.

    For livestock production, these include:
    • Producing sufficient environmentally friendly protein-rich raw materials for livestock feed while minimising the food versus feed competition for land
    • Improving protein quality in the raw materials used for livestock feed
    • Continuing investigations into alternative novel protein sources and appropriate regulation to allow use of animal protein by-products in livestock nutrition
    • Accurate assessment of animal requirements and feeding as they mature, particularly in group fed animals
    • Optimising microbial populations in the gut of all livestock to maximise efficiency of digestion and absorption, including the rumen
    • Models for describing nitrogen flows in food production that adequately values the up-cycling that occurs as nitrogen is captured from the environment and upgraded through plant and microbial protein to animal protein
    • How best to use nitrogen and other nutrients from animal manure to increase circularity of productive farm enterprises and systems

    Livestock play a key role in supplying human diets with high-quality protein. They are the reason we can provide nutritionally adequate diets, in terms of protein, to much of the world. Modern farming methods use a knowledge of protein nutrition to help create livestock feeds which maximise efficiency and profitability and provide high-quality pig and poultry products from small concentrations of plant and cereal protein and the upcycling of lower quality forage to produce milk and meat. The same concepts are important for managing the environmental footprint of livestock systems and understanding the roles livestock play in a sustainable food system.

    Livestock are complementary to food production from plants by:
    • Adding nutritional value to low-quality feedstock
    • Making use of by-products from the feed and food supply chains
    • Returning nutrients to land as manure to enhance soil health and sequester carbon

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    Why Protein Quality Matters in Livestock Production 

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