Strategies to reduce losses and improve efficiency of ruminant production systems rely on an optimal supply of rumen degradable nitrogen and an optimal efficiency of utilisation of absorbed amino acids. Reducing nitrogen excretion should be an opportunity for ruminants to produce more efficiently.
Product Manager Amino Acids
Kemin Animal Nutrition and Health – EMENA
Ruminant production systems convert vegetable protein into animal protein, contributing substantially to human nutrition by the production of milk and meat. Ruminal micro-organisms processes lignocellulose from low quality roughage into volatile fatty acids and energy, to transfer non-protein nitrogen into microbial protein. This is how ruminants can produce food of animal origin without competition for feed with non-ruminants and humans. Feed-efficient ruminant production is a complex system starting in many situations with a better nitrogen (N) efficiency (Flachowsky et al., 2013).
Depending on the animal species, ration, and management, between 5% and 45% of the nitrogen (N) in the vegetable protein is converted and deposited in the meat or milk. The other 55%-95% is excreted (urine or manure) and can be used as a source of nutrients for plant production (Oenema and Tamminga, 2005). However, the efficiency of re-conversion of the N into plant protein is limited. Only a maximum of 60% of the N applied to the soil can be converted to vegetable protein. The rest is lost, contributing to the environmental problem. This is especially important when we consider that the estimated overall amount of N excreted by animals is comparable with the annual consumption of N fertilizers, if not higher.
Strategies to reduce losses and improve efficiency of ruminant production systems rely on an optimal supply of rumen degradable N and an optimal efficiency of utilisation of absorbed amino acids (Dijkstra et al., 2013). Generally, in ruminants the observed efficiency of conversion between N consumed and N deposited into protein varies between 20 to 32%, but the maximum theoretical efficiency should be between 40 to 45% (Van Vuuren and Meijs, 1987; Hvelplund and Madsen, 1995; Dijkstra, 2013). A practical objective would be to achieve around 40% conversion, this goal can be reached by formulating for low crude protein (CP) and balancing for amino acids (AA’s), as described in this article.
Ruminant protein nutrition has three big challenges. Firstly, the rumen contains high numbers of micro-organisms which makes balancing the protein profile difficult, and typically leads to a very low feed and nitrogen efficiency. Secondly, it is not always easy to obtain high fodder quality which provides energy in enough quantity (minimum 40% of the total dry matter intake to avoid health problems and an even lower efficiency). Finally, it is crucial to ensure a good feed mixing process to avoid the cow sorting the feed by preference, and consequently running the risk of acidosis and low N efficiency.
Formulation is usually based on designing the least cost ration that provides the minimum level of required nutrients for a certain level of milk production however, the feed cost can be up to 70% of the total production cost. Improving efficiency of N conversion has one of the highest impacts on farm profitability (Tozer, 2012, McGrath et al., 2018, Bach, 2012).
Over the last few years, tremendous efforts and research have been made to refine the protein requirements of dairy cows. Our growing understanding of cow requirements has led to recognising two sets of protein requirements, rumen degradable protein (RDP), and rumen undegradable protein (RUP). Metabolically the cow has specific requirements for individual amino acids (AA’s), rather than metabolisable protein (MP). Together, the complex microbial metabolic activity in the rumen and intestinal processes make the study of N metabolism in ruminants more challenging than in the case of non-ruminants.
AA’s are the building blocks of milk and body proteins and are considered one of the most important nutrients in dairy cow nutrition. Many of these AA’s need to be supplemented in the diet because they can’t be synthesised quickly enough to meet the requirements of lactating cows. Therefore, these amino acids are known as essential AA’s. Inadequate supply of these essential AA’s can limit milk and milk protein yield. The essential AA’s that are present in MP is the smallest supply relative to the cow’s requirements and referred to as limiting AA’s. Methionine (Met) and lysine (Lys) have been recognised as the first limiting AA’s for lactating dairy cows under most feeding practices. This is fundamentally true because feed proteins have lower concentrations of Met and Lys, when compared to their concentrations in milk and microbial protein.
In European mid-range crude protein diets, it is not possible to meet the Met or Lys requirements with the use of dietary feed ingredients therefore, the use of rumen-protected supplements is needed. It is remarkable that Met and Lys work in synergy, as both AA’s are necessary in our diets for optimal and precise feeding, to achieve maximum production performance without overfeeding protein. Balancing dairy rations for AA’s, rather than CP%, is the state-of-the-art approach when it comes to protein nutrition.
Schwab et al. (2004) compared MP, Lys and Met supplies as predictors of milk production and milk protein yield. The results showed that Met and Lys supplies are better predictors of both milk production and milk protein yield than the supply of MP. This is because when one of the AA is limiting, this effectively causes an oversupply of all other AA’s to the cow. When the missing block (the limiting AA) is provided, a new molecule of milk protein can be synthesised. Therefore, the surplus of other amino acids will decrease, and the utilisation efficiency of MP will be improved. When dairy nutritionists rely only on the amount of MP available with no consideration for limiting AA’s the actual milk yield will – in almost all cases – be lower than expectation. This clearly indicates that although the supply of total MP might be adequate, the balance of the available AA’s can be incorrect, which limits milk production. It is widely accepted that by formulating with individual AA’s, the improvement in MP utilisation efficiency will provide the dairy nutritionist with an opportunity to formulate diets with lower CP content without compromising milk yield and milk components.
However, it is important to accurately predict the exact amount of metabolisable Met or Lys which can be used by the individual cow to reach this level of precision in our diets. Accurate and precise measurement techniques are imperative for obtaining reliable experimental results on N and AA utilisation. Knowing the rumen protection rate and intestinal availability of the RP-AA supplement, gives us the primary AA availability to the host animal (Hristov et al., 2019). Kemin’s experience indicates that when AA nutrition is implemented, applying the latest available nutritional knowledge and with the right rumen protected AA supplements (both methionine and lysine), improved animal performance with improved nitrogen efficiency (Table 1) is observed.
In conclusion, cutting-edge ruminant nutritionists are already balancing their diets for AA’s rather than crude protein. Adopting the concept of balancing for individual AA’s can bring endless opportunities for maximising dairy herd profitability. With continuously increasing protein feed prices and milk production costs, dietary reformulation using a lower crude protein content whilst balancing for AA’s, using rumen protected Met and Lys, can maximise MP utilisation, as well as dairy cow production, health, and fertility. Additionally, balancing for the first two limiting AA’s will decrease the overall N excretion to the environment, improving N and feed efficiency.
