Water use on non-irrigated pasture-based dairy farms: Combining detailed monitoring and modelling to set benchmarks.

Water use on the dairy farm is important to know how much should be provided for the animals, for cleaning purposes, for irrigation and general use. It is normally a surprisingly high figure which therefore should be well-managed. In intensively managed, confinement dairy systems water use because of relative ease of determination has been widely studied, but few reports exist regarding water use on pasture-based dairy farms. The objective of the study by Dr C.D. Higman and colleagues which was reported in the Journal of Dairy Science, Volume 100 of 2017, pages 828 to 840, was to quantify the seasonal pattern of water use to develop a prediction model of water use for pasture-based dairy farms. The title of their report was: Water use on non-irrigated pasture-based dairy farms: Combining detailed monitoring and modelling to set benchmarks.

Stock drinking, milking parlour and total water use was measured on 35 pasture-based, seasonal calving dairy farms in New Zealand over two years. The average stock drinking water was 60 litres per cow per day, with peak use in summer. Of concern was that, on average, 26% of stock drinking water was lost through leakage from water-distribution systems. The average corrected stock drinking water (considered as equivalent to voluntary water intake) was 36 litres per cow per day, and peak water consumption was 72 litres per cow per day in summer. Milking parlour water use increased sharply at the start of lactation (July) and plateaued (August) until summer (February), after which it decreased with decreasing milk production. The average milking parlour water use was 58 litres per cow per day (between September and February). Water requirements were affected by parlour type, with rotary milking parlour water use greater than herringbone parlour water use.

Regression models were developed to predict stock drinking and milking parlour water use. The models included a range of climate, farm and milk production variables. The main drivers of stock drinking water use were maximum daily temperature, potential evapo-transpiration, radiation, and yield of milk and milk components. The main drivers for milking parlour water use were average per cow milk production and milking frequency. These models of water use are similar to those used in confinement dairy systems, where milk yield is commonly used as a variable. The models presented fit the measured data more accurately than other published models and are easier to use on pasture-based dairy farms, as they do not include feed and variables that are difficult to measure on pasture-based farms.

Comments: (1) The average water intake per cow per day of 36 litres on pasture appear low, but it should be remembered that about 70-80% of the pasture mass which the cow consumes is also water. (2) The authors developed elaborate models of prediction which the reader can look up in paper, but an easy model (although less precise) is:

VWI model = 14.3 + 12.4 × milk yield + 0.32 × DM%, where VWI is voluntary water intake in litre per day and DM is the dry matter percentage of the pasture.