Over the last few years, tremendous efforts and research have been carried out to refine the protein requirements of dairy cows. Our growing understanding of cow requirements has led to recognition of two sets of protein requirements: ru- men-degradable protein (RDP) and rumen-undegradable protein (RUP). Metabolically the cow, of course, has specific requirements for individual AAs, rather than metabolisable protein (MP) per se. Together, the complex microbial meta- bolic activity in the rumen and processes in the intestines make the study of N metabolism in ruminants more challenging than in the case of non-ruminants.


Amino acids AAs 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 AAs need to be supplemented in the diet, because they cannot be synthesised quickly enough to meet the requirements of producing cows. Therefore, these amino acids are known as essential AAs. Inadequate supply of these essential AAs can limit milk and milk protein yield. The essential AA that is present in MP in the smallest supply rela- tive to the cow’s requirements is referred to as the limiting AA. Methionine (Met) and lysine (Lys) have been recognised as the first limiting AAs for lactating dairy cows under most feed- ing practices. This is fundamentally true because feed pro- teins have lower concentrations of Met and Lys when com- pared to their concentrations in milk and microbial protein. Mid-range CP diets in Europe are unable to meet Met or Lys needs with the use of dietary feed ingredients, therefore the use of rumen-protected supplements is needed. It is remarka- ble that Met and Lys work in concert: both AAs are necessary for the best precise feeding to achieve the maximum produc- tion performance without overfeeding protein. Balancing dairy rations for AAs, 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 re- sults showed that Met and Lys supplies are better predictors of both milk production and milk protein yield than the sup- ply of MP. This is because when one of the AAs is limiting, this effectively causes an oversupply of all other AAs to the cow. When the missing block (the limiting AA) is provided, a new molecule of milk protein can be synthesised. Therefore, sur- plus of other AAs decreases and the utilisation efficiency of MP improves. When dairy nutritionists rely only on the amount of MP available with no consideration for limiting AAs, the actual milk yield will – in almost all cases – be lower than expected. This clearly indicates that, although the sup- ply of total MP might be adequate, the balance of the availa- ble AAs can be incorrect, which limits milk production. It is widely accepted that, by formulating with individual AAs, the improvement in MP utilisation efficiency will provide the dairy nutritionist with an opportunity to formulate diets with


lower CP content without compromising the yield of milk and milk components. However, it is important to accurately predict the exact amount of metabolisable Met or Lys that can be used by the individual cow to reach this level of precision in our diets. Ac- curate and precise measurement techniques are imperative for obtaining reliable experimental results on N and AA utili- sation. Knowing the rumen-protection rate and intestinal availability of the RP-AA supplement gives us the primary AA available to the host animal (Hristov et al., 2019). According to Kemin’s experience, when AA nutrition is implemented ap- plying the latest available nutritional knowledge and with the right rumen-protected AA supplements (both methionine and lysine), better animal performance with better nitrogen efficiency (Table 1) is observed. In conclusion, cutting-edge ruminant nutritionists are already balancing their diets for AAs rather than for CP. Adopting the concept of balancing for individual AAs can bring endless op- portunities for maximising dairy herd profitability. With con- tinuous increases in feed prices and milk production costs, diet reformulation with low CP content while balancing for AAs and using rumen-protected Met and Lys can maximise MP utilisation as well as dairy cow production and health. Ad- ditionally, balancing for the first two limiting AAs will de- crease the overall N excretion to the environment, improving N and feed efficiency.


▶DAIRY GLOBAL | Volume 7, No. 3, 2020 49


PHOTO: HANS PRINSEN


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60