1. Executive Summary
This review summarises our current understanding of the impact of water quality on the productivity of livestock, with special reference to the situation as it may relate to New Zealand livestock farmers.
In fact, there is a dearth of information on the topic, although various sets of guidelines have been produced around water quality for livestock including publications from Australia and New Zealand However, the guidelines are often based on very little, or even conflicting data. The focus of the guidelines is mainly around toxicity, or "trigger" levels (the level at which there is minimal risk to animal health, but if levels exceed such levels, the risk to stock should be investigated). These levels are expected to be much higher than those that would influence productivity.
Numerous publications note the importance of water quality but there is little experimental evidence as to what actually constitutes quality from the perspective of the productivity of ruminants. There is evidence for the importance of salinity and total dissolved solids (TDS), and for faecal contamination. The most substantive studies are from Canada, where the impact of clean water has been quantified. These studies recorded an array of water components, but the researchers concluded that the detrimental effect of the dirty water was due to faecal contamination influencing palatability and hence consumption, rather than by stress induced by pathogens, toxins, or parasites. Cattle that drank clean water spent a longer time grazing and, in penned studies, ate more of the food on offer.
Studies with faecally-contaminated water clearly showed an influence of such contamination on consumption. This points to management strategies such as fencing to exclude animals from riparian zones, dams and water-courses to avoid contamination, pugging and detrimental effects on waterways.
This review highlights the dearth of information but indicates the importance of deriving relevant information for New Zealand farmers so that they can then look at the issues from their own local perspective. From this perspective, the most important issues are likely to be faecal contamination, mineral content (especially TDS), and perhaps nitrate and iron. Thus, these issues are those that should be the highest priority for research in New Zealand.
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