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Nitrogen use in dairy cows at pasture and consequences for the environment

Thesis : nitrogen use in dairy cows at pasture and consequences for the environment
The objective of the thesis is to study the effect of tannins addition in the diet of dairy cows on animal performances and assess the consequences of grazing on the environment.
paturage_bresil_reduit

Improve the efficiency of nitrogen use and reduce losses towards the environment

Meet the requirements of metabolisable protein is critical for dairy cow performances. Temperate climate pastures generally have protein level capable to exceed the ruminal microbial nitrogen demand, resulting in an inefficient use of dietary protein and losses towards the environment. The same can occur in diets supplemented with high protein concentrate.

Inclusion of condensed tannins in the diet of dairy cows

The condensed tannin (CT) can reduce the ruminal protein degradation and thus increase the use of dietary protein with positive effects on milk production. The first part of the thesis, realized in Brasil (Lages University) therefore aimed at testing the addition of CT (Acacia mearnsii) in the diet of dairy cows at pasture.

  • In a first experiment, three groups of three lactating cows grazed a mixed temperate pasture (Ray-grass and oat) during three periods of 21 days. Three treatments were compared: no supplementation, a supplementation with 4 kg of maize grains per day and a supplementation with 4 kg of maize grains per day with 20 g/kg of CT extract. The supplementation increased milk production by 2.5 kg/cow/day compared with the no supplementation treatment. However, the addition of CT did not have any effect on animal performances.
  • A second experimentation was then conducted to evaluate the effect of a supplementation with maize and soybean meal with or without the addition of tannins for dairy cows grazing tropical pastures (Pennisetum americanum). Some measurements of enteric methane production were also realized. The results of this experiment are still under treatment.

Measure gas emissions of cows fed with fresh grass

The second part of the thesis just began in France (INRA UMR Pegase). Two experiments are currently conducted at the experimental farm in order to assess the consequences of a diet based on fresh grass on nitrogen use by dairy cows and on gas emissions (ammonia and greenhouse gases).

 

vache litière accumulée paille
appareil_mesure_N2O_IEPL_reduit

 

  • The first experiment will consist in a comparison of lactating cows’ performances and nitrogen use efficiency when fed with a maize silage and soybean meal diet or with fresh grass and hay. The cows will be conducted on a straw deep litter during 4 weeks and gas emissions (CO2, CH4, NH3, N2O) will be measured at the barn level.
  • At the same time, a second experiment will be conducted to measure ammonia (NH3) and nitrous oxide (N2O) emissions from dairy cows at pasture (grazing and receiving hay) using different measurement methods.

All these results will help to propose animal management strategies both more efficient in terms of nitrogen use and more environmentally friendly.

The thesis of Tiago P. Alves is a sandwich thesis partially conducted in Brazil (State University of Santa Catarina, Lages) with a stay of 7 months in the Syslait team of UMR Pegase.

Contact

Nadège Edourad, team dairy systems (nadege.edouard[at]rennes.inra.fr)