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Our objectives

The efficiency of nitrogen utilization for milk production in dairy cows is only 0.27 to 0.30. The urinary nitrogen excretion accounts for about one-third of the nitrogen intake, the remainder is excreted in the feces. It is possible to increase the efficiency of nitrogen utilization and to reduce urinary nitrogen excretion of dairy cows by reducing the metabolizable protein (MP) supply (called PDI in the INRA system). However, with diets below 95 g PDI/kg dry matter (DM) in INRA (2007), milk protein yield decreases strongly. Another possibility is to better balance the essential amino acid (EAA) content of MP, in particular for Lys and Met. The effect of balancing Lys and Met has only been tested using a high levels of MP supply (> 100 g PDI/kg DM, INRA, 2007).
  However, it was not known whether balancing the EAA profile at a lower level of MP (<100 g PDI/kg DM, INRA, 2007) could also increase milk protein yield and the efficiency of MP utilization. In addition, it was important to understand if these effects can be explained by changes in mammary uptake of EAA. Lastly, EAA other than Lys and Met may be involved in the efficiency of MP and need to be identified.

Convincing results

• Balancing the EAA profile increased milk protein yield and the efficiency of MP utilization by about 8 % both at low and high MP supplies, with no interaction.
• The increased milk protein yield observed both when increasing the MP supply or when balancing the EAA profile was explained by an increase in mammary uptake of limiting EAA. When increasing the MP supply (+16%), a larger amount of non-essential AA was absorbed. They were not taken up by the mammary and were catabolized since plasma urea concentration increased and the efficiency of MP utilization decreased (-13%). This was not the case when balancing the AA profile since the total amount of intestinal AA absorbed was not increased but the mammary uptake of some EAA increased.
• With a maize silage diet, the maximum increase in efficiency was observed by balancing 4 EAA (Lys, Met, His, and Leu). However, a study on Val or Ile deletion indicated that it was important to better balance the 3 branched-chain AA together (ratio between Leu, Val, and Ile). An excess of one of these AA may result in the catabolism of all the 3 branched-chain AA.

This work was conducted as part of the thesis of Muhammad Naveed Ul Haque between 2009 and 2012 and in the European project Rednex. It will continue by publishing all the experiments and including some concepts from this research on our project for our new INRA ruminant feeding system (Systali project).

For Futher Information

Haque, M.N., H. Rulquin, A. Andrade, P. Faverdin, J.L. Peyraud, S. Lemosquet. 2012. Milk protein synthesis in response to the provision of an "ideal" amino acid profile at 2 levels of metabolizable protein supplies in dairy cows. J. Dairy Sci. 95:5876-5887. (DOI)

Haque, M.N. 2012. Milk protein yield in response to amino acid profiles at different levels of metabolizable protein supply in dairy cow (Thèse de doctorat, Institut Supérieur des Sciences Agronomiques, Agroalimentaires, Horticoles et du Paysage (Agrocampus Ouest), FRA). [Link]

Haque, M.N., H. Rulquin, S. Lemosquet. 2013. Milk protein responses in dairy cows to changes in postruminal supplies of arginine, isoleucine, and valine. J. Dairy Sci. 96:420-430 (DOI)

Lemosquet, S., Haque, M.N., Faverdin, P., Peyraud, J.-L., Delaby, L. 2014. Balancing the amino acid in dairy diets increased milk protein yield and efficiency at low level of metabolizable protein similary as at high level. 21e Rencontres autour des Recherches sur les Ruminants, Paris, 2014-12-03 - 2012-12-04. Paris : Institut de l'Elevage (in press).

Contact

Sophie Lemosquet, team physiology of lactation and milk synthesis (sophie.lemosquet[at]rennes.inra.fr)