Water Imperative

If you won't drink the water you offer to your cows, then its too dirty for them.

Drinking water is the most important nutrient for lactating dairy cattle. Milk is composed of 87 per cent water and the body of a mature cow consists of between 45 and 75 per cent water.

Lactating dairy cattle consume approximately four to five litres of water for every kilogram of dry matter intake, a total of between 80 and 120 litres of water daily.

Many factors can affect water consumption by lactating diary cattle. The most important are milk production, dry matter intake (DMI), composition of the diet, ambient temperature and humidity, water supply, and water quality. Approximately 20 years ago researchers at the University of Illinois attempted to develop guidelines to predict water consumption based upon these factors. A regression equation was developed by Dr. Murphy to predict water intake as follows:

Water intake (kg/day) = 16 + 1.58 x DMI (kg/day) + 0.90 x milk production (kg/day) + 0.05 x sodium intake (g/day) + 1.2 x minimum temperature (degrees C).

Due to the size of the variables and their range, milk production and DMI have the greatest effect on water intake. Assuming sodium content in the diet of 0.40 per cent (DM basis) and a minimum daily temperature of 10C, then Murphy's equation predicts water intakes (kg/day) for lactating cows as shown in Figure 1.

Figure 1
Variable 20 KG 30 KG 40 KG
Dry matter intake (kg) 18.0 21.0 24.0
Constant 16.0 16.0 16.0
Dry matter intake variable 28.4 33.2 37.9
Milk production variable 18.0 27.0 36.0
Sodium intake variable 3.6 4.2 4.8
Minimum temperature variable 12.0 12.0 12.0
Total water intake 78.0 92.4 10106.7

Given the large correlations between water intake, DMI and milk production, then the importance of unlimited supply of high quality drinking water for lactating cows is apparent. If water consumption is limited due to lack of access or due to poor quality water, both DMI and milk production can potentially be severely reduced.

The prediction equation for water intake also illustrates the importance of water supply during hot weather for lactating cows. If the minimum daily ambient temperature rises to 20C from 10C, then the drinking water requirement increases by 12 litres per day for all levels of milk production.

Providing access to plenty of fresh, clean water is essential to allow for maximum consumption, especially following milking when 50 to 60 per cent of drinking takes place. For free stall barns and parlours current recommendations include the following:

In tie stall barns, each cow should ideally have her own water bowl. Bowls need to be kept clean, in good working order, and high rates of water flow maintained during times of peak demand at milking and feeding. Swedish research has shown that time spent drinking was reduced and water consumption was increased as water flow rate increased up to 12 litres/min into the drinking bowl. The minimum diameter for water supply pipes is 1 inch (2.5 cm).

Research has shown that cows prefer warm water (15-25C is optimum) during cold weather. Providing warmed drinking water during cold weather many increase water consumption. However, providing chilled water during hot weather does not increase water intake according to the research.

Drinking water quality criteria include: odour and taste, pH, total dissolved solids (TDS), hardness, excess sulphates, iron, nitrates, toxic substances such as heavy metals and organophosphates, and micro-organisms such as total coliform and fecal coliform bacteria and algae.

In-depth discussion of water quality effects on dairy cattle is beyond the scope of this article. However, water quality does negatively affect milk product, DMI and health more than we often realize.

Several studies have investigated the effect of elevated levels of TDS or salinity in drinking water on lactation in dairy cattle. There was wide variation in the studies on what level of TDS in water begins to have a negative effect. In some cases levels as low as 2500 ppm TDS can have a negative effect on milk production, although the National Research Council recommends TDS of less than 5000 ppm for lactating dairy cattle.

Elevated levels of sulphates in drinking water can reduce water intake, DMI and milk production, cause diarrhea, and cause reproductive and health problems. Sulphates may give a characteristic rotten egg smell to water.

Sulphates in water may compromise the immune system, leading to reproduction and health problems, by reducing the availability of important minerals, including copper, manganese, zinc and selenium. Although cattle may tolerate sulphate levels as high as 1500-2500 ppm in drinking water, performance is often compromised at levels as low as 500 ppm.

Nitrate levels of 300-400 ppm in drinking water have been associated with reproductive problems and abortions in dairy cattle. Nitrates may also be high in feeds, so the maximum tolerable level in water depends on the level in the feed.

There is no research defining the optimum water pH for dairy cattle. It is thought that the optimum pH is approximately neutral (6.5 - 7.5). Drinking water in Ontario often is fairly alkaline, with pH testing up to 8.5. According to testimonials elsewhere, lowering water pH to approximately 7.0 may enhance water intake, DMI and milk production.

There is very little published research on the effects of coliform bacteria in drinking water of dairy cattle. The presence of any coliform in water may be cause of scours in young calves, but older cattle can tolerate up to 50 coliform / 100 ml according to one report.

Inadequate water supply or poor water quality can be significant limitations to milk production, feed intake, cow health and profitability for dairy herd. Water is the most important nutrient for dairy cows. Ensuring that they have unlimited access to fresh, clean and high quality water will always pay dividends.