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Environmental Impact of Ruminant Production (Nitrogen surplus: Dairy (18.7…
Environmental Impact of Ruminant Production
Nitrogen surplus: Dairy
18.7 billion Kg of protein fed in the EU but only 4.7 billion Kg converted into milk protein
On average farms have a surplus of 68 kg N/ha Land
Within the Cow 75% of consumed nitrogen is wasted and excreted through faeces (25-40%) urine (15-45%)
Nitrogen use efficiency (NUE) can be calculation by milk nitrogen output divided by diet nitrogen intake
Ruminants are the least efficient at converting nitrogen
Efficiency within the Rumen
Grasses high in water soluble carbohydrates (WSC) mean increased fructan levels
Fructans are also higher in the afternoon, Cattle allocated afternoon grazing will grow faster than in the morning
initially nitrogen application increases WSC but this peaks at around 300 kg/ha after which any additional nitrogen applied causes a reduction in WSC levels
Breeding for high WSC varieties is taking place, it has been found that as the levels of WSC increase so does the DM digestibility
Studies have shown that feeding these WSC can decrease nitrogen output
WSC content also shown to decrease urine N output with 9 WSC/N (g-g-1) being optimum
Roles of WSC in the rumen
Supply of energy- Fructans are 100% digestible
Sparing of Amino acids
Plant cell membrane and protein protection - slow release of plant proteins/amino acids
Production of Human edible food
Competition between livestock and humans for food
Although the least effective at converting nitrogen dairy cow diets contain less human edible food than broiler chickens (0.36:0.75)
Suckler beef, poultry meat and eggs provide more human edible protein than is consumed by the animal
Using nitrogen on forage
Three sources of nitrogen to forage, Animal returned nitrogen, Fertiliser nitrogen, Legume fixed nitrogen
25-40% lost as nitrates, 8-14% lost through denitrification (N2O), 5-20% lost through nodule leachate. On average 50% of applied nitrogen is wasted
For grass especially there is a ceiling after which applying more fertiliser is not economical. Must also consider toxicity problems with excess nitrogen
Feeding reduced protein to growing heifers
Aim: increase efficiency of dietary N use in dairy systems
Findings indicated that feeding less protein to growing heifers did not significantly affect growth and may increase the overall lifetime N use efficiency