Limiting grazing periods combined with proper housing can reduce nutrient losses from dairy systems

Authors: MCDOWELL, RICHARD - Lincoln University - New Zealand; Rotz, Clarence - Al; OENEMA, JOUKE - University Of Wageningen; MACLNTOSH, KATRINA - Dairy Nz, Ltd

Submitted to: Nature Food
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2022
Publication Date: 12/8/2022
Citation: McDowell, R., Rotz, C.A., Oenema, J., Maclntosh, K. 2022. Limiting grazing periods combined with proper housing can reduce nutrient losses from dairy systems. Nature Food. 3:1065-1074. https://doi.org/10.1038/s43016-022-00644-2.
DOI: https://doi.org/10.1038/s43016-022-00644-2

Interpretive Summary: An increasingly affluent global population is demanding more livestock derived produce, but in tandem with improved environmental and animal welfare standards. Dairying has been identified as a contributor to water quality deterioration in many jurisdictions. Nutrient losses of nitrogen and phosphorus are important factors contributing to poor water quality via algal blooms in surface waters and direct toxicity from high nitrate concentrations in drinking water. Some studies have suggested that grazing systems perform better in some regions than confined systems by certain ‘sustainability’ metrics. However, little empirical data exist to support these claims with respect to nutrient losses to water. Hence, we aimed to determine if differences exist between contrasting dairy production systems based on the duration of outdoor grazing, with a focus on their nitrogen and phosphorus losses as indicators of water quality. We found insufficient evidence that grazed dairy as a system reduces nutrient losses compared to confined systems. We suggest that the use of a hybrid system may allow for duration-controlled grazing, uniform distribution of stored excreta during periods of low nutrient loss risk, controlled dietary intake, and the mitigation of animal welfare issues during weather extremes.

Technical Abstract: The demand for dairy produce is growing alongside concerns about the impact of dairying on water quality due to nutrient loss. Pasture-based and grass-fed branding is used to justify product premiums based on consumer perceptions of improved human health as well as better environmental performance and animal welfare. We contrasted global observational (n = 156) data for losses of nitrogen (N) and phosphorus (P) from land to water by the duration of outdoor grazing: less than or equal to 2, less than or equal to 9, and between 3-8 months, corresponding to grazed, confined, and partially housed hybrid systems. Observational N losses for confined systems were lowest on a productivity basis (g kg-1 fat and protein corrected milk) but not on an area basis. No differences were noted for P losses between the systems. Modelling of the three dairy systems in New Zealand, United States, and the Netherlands using the Integrated Farm System Model yielded similar results. We found insufficient evidence that grazed dairy as a system reduces nutrient losses compared to confined systems. We suggest that the use of a hybrid system may allow for duration-controlled grazing, uniform distribution of stored excreta during periods of low nutrient loss risk, controlled dietary intake, and the mitigation of animal welfare issues during weather extremes.