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Improving protein efficiency

To reduce environmental impact of dairy cattle, increasing nutrient efficiency for milk synthesis is important.  A better understanding of the animal's responses to nutrients could improve this efficiency.
Reducing metabolizable protein supply (i.e. Protein Digestible in the Intestine in INRA, 2018) greatly improves protein efficiency. However, it can decrease milk and protein yields, and consequently reducing milk payments. An improved amino acids (AA) profile can partially compensate the decrease in milk protein yield without increasing metabolizable protein supply. This can be explained in the mammary gland by an increase in AA uptake and their export in milk proteins. However, improving the AA profile does not always result in a recovery of milk yield. This effect could depend on the lactation stage. Indeed, the mechanisms explaining the decrease in milk yield when metabolizable protein supply decreased have not yet been well studied. In addition, the milk yield strongly depends on the level of energy supply and the type of energy. Milk yield was reported to increase when using high starch diets.

How do nutrients alter milk yield?

The cows use the majority of its energy supply (about 70% of the net energy for a cow producing 40 kg /d) to synthesize milk components (proteins, fatty acids and lactose) in the mammary gland. Cows metabolize many sources of energy in the liver and mammary gland (glucose, volatile fatty acids, fatty acids, AA). However, the mammary gland does not use these different nutrients via the same pathways, which then affect milk composition. During this PhD, a meta-analysis approach will be used to understand how the mammary gland modulates milk yield and composition in response to these different nutrients.

Reasoning throughout lactation

The effects of type of nutrients, mainly increasing AA or glucogenic nutrients independently of increasing net energy supply, has largely been studied in the short-term experiments, in mid-lactation. The longer-term effects of AA and energy sources should be investigated in more detail. Indeed, AA requirements seem to vary during lactation. They would be greater at the beginning of lactation than at the end. Also, the energy partitioning changes during lactation. The animal mobilizes its body reserves at the onset of lactation and then the animal recovers them gradually. This partitioning could depend on the energy sources used. As part of this PhD, a trial is underway to study the effect of AA and energy sources at different stages of lactation on the efficiencies of nutrient utilization for milk synthesis. This trial will both focus on performance and on physiological parameters to better explore the different components of metabolizable protein efficiency.

Jean-Charles Anger is a PhD student since December 2020 for 3 years. He is supervised by Sophie Lemosquet in the Alimentation and nutrition team, Christelle Loncke of UMR INRAE- AgroParisTech Mosar and Romain Bidaux, CARGILL.

Contact

Jean-Charles Anger: jean-charles.anger[at]inrae.fr (PhD student)
Sophie Lemosquet: sophie.lemosquet[at]inrae.fr (PhD supervisor)
Christelle Loncke: christelle.loncke[at]agroparistech.fr (PhD co-supervisor)
Romain Bidaux: romain_bidaux[at]cargill.com (PhD co-supervisor)