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Mineral nutrition of dairy cows

During lactation, cows export a huge amount of calcium in milk and its bones are particularly mobilized. It is necessary to have a better knowledge of bone metabolism during lactation to have a more accurate estimation of needs in calcium and phosphorus of dairy cows. The aim is to:

• have a better control in calcium intake to avoid a restricted bone reconstitution during lactation
• reduce recommended phosphorus intake for those animals to limit phosphorus rejects, which may be involved in eutrophization.

The biggest difficulty is that bone cycles are hard to identify on large herds of dairy cows. Actually, it is easy to follow calcium concentration in milk during lactation with Mid-infrared, and it may be an indirect indicator of those cycles. It has recently proved that in lactating mammals that calcium levels regulation may impact on both bone regulation and calcium excretion in milk.

Calcium and bone cycle during lactation

The working hypothesis of this thesis is that dynamic of milk calcium content during lactation reflects dynamic of bone accretion and resorption in dairy cows and therefore that the monitoring milk calcium content can be a useful tool for characterizing bone accretion and resorption cycles in dairy systems, and for reasoning the mineral nutrition of dairy cows in a dynamic way during lactation. The central questions of this thesis will be to determine:

• the relationship between the dynamic of milk calcium and that of bone accretion and resorption on the same individual during lactation,
• the dynamic of bone accretion and resorption can be significantly modulated by the dynamic of mineral supplementation during lactation,
• the fact of reasoning mineral supply throughout lactation may allow significant reduction in calcium and phosphorus supplementation without penalizing bone reconstruction of cows.

The first task of this thesis will be to monitor jointly dynamic of milk calcium during lactation and those of serum levels of biomarkers of bone accretion and resorption on long term experiment already running on the Inra experimental farms of Le Rheu (Méjusseaume) and Le Pin au Haras (120 cows involved).
A parallel task will be to analyze data already available at UMR Pegase consisting in surveys of feed practices of farms spread over France associated with an annual monitoring the calcium content for individuals . These data will allow defining a range of herd feeding practices, from farms, susceptible to modulate milk calcium content during lactation.
Finally, a specific trial will compare two targeted feeding strategies for their ability to modulate milk calcium content and/or bone accretion and resorption cycles through serum biomarkers. Those measures will be supplemented by measurement of urinary and fecal excretion of calcium and phosphorus, body retention of those elements and the bone composition thanks to biopsy.

Pierre Gaignon is working on this subject of thesis since the 1^st november of 2015 for 3 years. He is supervised by Anne Boudon in the team Alimentation and Nutrition.

Contact

Pierre Gaignon : pierre.gaignon[at]rennes.inra.fr (PhD student)
Anne Boudon : anne.boudon[at]rennes.inra.fr (supervisor)
Catherine Hurtaud : catherine.hurtaud[at]rennes.inra.fr (co-supervisor)