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Environmental, economic and protein autonomy issues

Increasing metabolisable protein efficiency for milk protein synthesis is an important environmental, economic and protein autonomy issue for dairy nutritionist.
This efficiency partly depends on the metabolic fate of AA, the nutrients actually absorbed in the small intestine after the hydrolysis of metabolisable proteins. Indeed, the absorbed AA are either used to resynthesize different proteins synthesised by the cows, mainly milk protein and metabolic faecal protein, or catabolised into urea. However, protein synthesis and turnover is a costly process in term of energy.
The aim of this work was to understand the variations in metabolisable protein and individual AA efficiencies in response to net energy supply (starchy diets or post-rumen glucose). The effects of net energy supply were studied either in interaction with two levels of MP supply (i.e. two amounts of total AA supplies) or in interaction with 2 AA profiles (Low and high supplies in lysine, methionine and histidine) in dairy cows. For this, we analysed mammary and liver metabolism.

An original approach to assess amino acid catabolism based on the INRA (2018) feeding system

The catabolism of essential AAs was assessed both by measuring portal, hepatic and mammary gland net fluxes of AA and by calculating whole body efficiency of each essential AA (EAA) using INRA (2018) : the inefficiency is an estimate of AA catabolism. The efficiency of each individual EAA was calculated from the metabolisable protein (MP) efficiency (expressed as PDI efficiency in INRA, 2018 for Protein Digestible in the Intestine) proposed in the INRA (2018) ruminant feeding system. The MP efficiency corresponds to the ratio between the sum of export proteins (milk protein yield and metabolic faecal, scurf, gestation etc.) by the animal and the digestible protein intake (Figure 1; INRA 2018). It was combined with the EAA profiles of the different protein exported (milk, metabolic faecal, scurf) to define individual EAA efficiencies.

Metabolisable protein and AA efficiencies in response to net energy or/and metabolisable protein supplies

The increased MP efficiency observed with increasing net energy supply was explained by an increase in milk protein yield without any increase in MP supply.
In one hand, increasing net energy supply increased mammary uptake of histidine, methionine, phenylalanine and tyrosine (group 1 AA according to Mepham, 1982), and of some non-essential AA. On the other hand, the mammary catabolism of lysine, isoleucine, leucine and valine (group 2 AA) and the hepatic catabolism of group 1 AA decreased in parallel.
Metabolisable protein efficiencies decreased with increasing MP supplies because milk protein yield and mammary uptake of AA increased to a lesser extent than AA supplies. At the same time, hepatic catabolism of AA from group I and mammary catabolism of AA from group 2 increased. These different mechanisms would explain the additivity of the observed increases in milk protein in response to increasing, both net energy and MP supplies.

Finally, the MP efficiency could rely on the most limiting EAA presenting the highest efficiency. This shows the importance of considering the efficiencies by AA and not only the MP efficiency (PDI) in a future feeding system for dairy cows.
The effects of starchy  energy diets and better balancing AA supply on nitrogen, MP and AA efficiencies will be studied (see also the PhD project of Jean-Charles Anger) at different stages of lactation in order to improve the estimates of individual EAA efficiency in feeding systems.

This project was conducted in partnership between INRAE UMR PEGASE (S. Lemosquet) and Agriculture and Agri-Food Canada (H. Lapierre) within the framework of a Cifre PHD student (C. Omphalius) with the company ADISSEO (L. Bahloul).

Bibliography

• Omphalius, C., Lemosquet, S., Ouellet, D.R., Bahloul, L., Lapierre, H. (2020). Postruminal infusions of amino acids or glucose affect metabolisms of splanchnic, mammary, and other peripheral tissues and drive amino acid use in dairy cows. Journal of Dairy Science, 103 (3), 2233-2254. [DOI], [HAL].
• Omphalius , C., Lapierre, H.,  Bernard, L., Bahloul, L., Lemosquet,S .(2020). Responses to methionine, lysine plus histidine and energy supply on mammary metabolism in dairy cows. Presented at: EAAP 2020 Virtual Meeting. 1^st-4^th December 2020. [HAL].
• Omphalius, C. Lapierre, H., Guinard-Flament, J., Lamberton, P., Bahloul, L., Lemosquet, S. (2019). Amino acid efficiencies of utilization vary by different mechanisms in response to energy and protein supplies in dairy cows. Journal of Dairy Science, 102 (11): 9883-9901. [DOI], [HAL].
• Omphalius, C., Lapierre, H., Bahoul, L., Lemosquet, S. (2019). Responses to methionine, lysine plus histidine at two levels of energy in dairy cows. Presented at: 6. International Symposium on Energy and Protein Metabolism (Isep), Belo Horizonte, br (2019-09-09 - 2019-09-12), [DOI], [HAL].
• Omphalius, C., Lemosquet, S., Ouellet, D.R., Bahoul, L., Lapierre, H. (2019). Protein and energy affect splanchnic and mammary metabolisms and drive amino acid use in dairy cows. Presented at : 6. International Symposium on Energy and Protein Metabolism (Isep), Belo Horizonte, br (2019-09-09 - 2019-09-12). [DOI], [HAL].
• Omphalius, C., Lapierre, H., Bahloul, L., Lemosquet, S. (2019). Methionine, lysine, and histidine supplementation at low and high net-energy supply in dairy cows. Presented at: Adsa Annual Meeting, Cincinnati, us (2019-06-23 - 2019-06-26). [HAL].
• Omphalius, C., Lapierre, H., Guinard-Flament, J., Bahloul, L., Lemosquet,  S. (2018). L’efficience d’utilisation des acides aminés varie via des mécanismes différents lors d’apports contrastés d’énergie nette et de protéines digestibles dans l’intestin. Presented at: Rencontres autour des recherches sur les ruminants (3R), Paris, fr (2018-12-05 - 2018-12-06). [HAL].