Manipulation of the ruminant gastrointestinal tract microbiomes for reduced environmental impact of nitrogen excretion from dairy cows

Nitrogen use (NUE) in ruminants is low, typically 25-30%, with the remaining nitrogen being excreted in urine, and some in the faeces. When faeces and urine mix, N is lost as ammonia which causes terrestrial eutrophication. Furthermore, during slurry storage and following soil application a portion of the N can be converted by bacteria into nitrous oxide, a GHG with a 298-fold greater global warming potential than carbon dioxide. Nitrogen loss in waterways via leaching can also cause aquatic eutrophication and biodiversity loss. In addition, nitrogen (protein) feeds are increasingly costly and the low nitrogen use represents an economic loss for farmers. However, despite these environmental and economic challenges, dairy cows are in general offered diets containing excess nitrogen. Current environmental and economic challenges mean that over-feeding nitrogen to ruminants is no longer viable.

The hypothesis of this project is that, through an improved understanding the role of the rumen microbiome, and the linkages to RFI, dairy cows can be offered diets containing lower protein levels with minimal loss in milk production and with significant environmental benefits.
The project aims to 1. Use in vitro rumen-simulating techniques to assess the effects of varying dietary protein level on gas production, volatile fatty acids, methane production and the rumen microbes; 2. Assess the effects of varying protein feeding levels in a lactating dairy cow experiment on milk yield, milk composition (including fatty acid profiles), body condition, cow health, ration digestibility, and the rumen, buccal and faecal microbiome 3. Investigate the use of proxies for nitrogen use efficiency and other production parameters, for example FTIR of dairy cow digesta, milk fatty acids etc. Consequently, this project encompasses animal science, microbiology and computational biology