Effect of genotype and feeding regime on enteric methane, non-milk nitrogen and performance of dairy cows during the winter feeding period

The objective of the study was to determine the effect of genotype and feeding regime on enteric methane production, non-milk nitrogen and production performance during the winter feeding period. Two sets of traits were studied in four dairy production systems. One set of traits, represented the polluting effect of dairy cows to the environment and the other represented cow production performance. To quantify the impact of dairy cows on the atmospheric environment, enteric methane per kg milk was estimated while non-milk nitrogen was estimated to quantify the potential pollution of dairy cows to ground water resources. The cow performance traits were energy corrected milk yield (ECM) and body energy content (EC). After correcting for systematic factors, highly significant differences were found between the production systems on their impact on the environment. Generally, an increase in production performance in terms of milk yield was associated with a decrease in enteric methane production per kg of milk. However, non-milk N per kg milk increased in the average genetic merit groups while non-milk N per ha increased in the more intensive production systems. This apparent trade-off highlights the importance of the need to incorporate the dynamics of emission burden and pollution potential of different dairy systems when characterising different dairy systems. Including the environmental cost of dairying in the general description of different dairy production systems will not only improve productivity but also not compromise the environment.