REVIEW PAPER
A review of efficiency of nitrogen utilisation in
lactating dairy cows and its relationship with
environmental pollution
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1
The University of Reading, Centre for Dairy Research, Department of Agriculture,
Earley Gate, P.O.Box 236, Reading RG6 6AT, United Kingdom
2
Present address: EEA Rafaela INTA Casilla de correo 22, (2300) Rafaela, Santa Fe, Argentina
Publication date: 2000-01-13
Corresponding author
E. Kebreab
The University of Reading, Centre for Dairy Research, Department of Agriculture,
Earley Gate, P.O.Box 236, Reading RG6 6AT, United Kingdom
J. Anim. Feed Sci. 2000;9(1):1-32
KEYWORDS
ABSTRACT
The objective of this paper is to review the literature concerning nitrogen utilisation in lactating
dairy cows with an emphasis on their contribution to environmental pollution. Nitrogen, as oxides or
ammonia, is one of the green houses gases contributing to air pollution and through leaching to
rivers and ground water resources. A quantitative analysis of the contribution of dairy cows to
pollution at the farm level is given and the effect of different types of carbohydrate and protein
supplementation discussed. The relationship between nitrogen intake and nitrogen balance was investigated using data from 580 dairy cows and 90 treatments published in the literature. Regression
analysis described the relationships between nitrogen intake and output in faeces, urine and milk.
Inefficient utilisation of nitrogen by dairy cows indicates that about 72% of consumed nitrogen is
excreted in faeces and urine. There were positive linear relationships between nitrogen intake and
output in faeces, urine and milk up to an intake of 400 g N/d. However, above 400 g N/d, excretion
in urine increased exponentially while the rate of increase in nitrogen excretion in faeces and milk
declined linearly. To reduce nitrogen pollution, it is recommended to decrease the amount of crude
protein in the total diet to approximately 150 g/kg DM which compared with levels of 200 g/crude
protein/kg DM consumption can reduce annual nitrogen excretion in faeces by 21% and more importantly in urine by 66%. Management practices with respect to silage making and the choice of
supplements need to be considered with the aim of reducing total nitrogen in excreta and if possible
shifting nitrogen excretion from urine to faeces.
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