Water: a forgotten nutrient

Milk is comprised of 87% water and a cow’s yield is directly related to the amount of water in its body. As an essential nutrient, it is second only to oxygen in its importance in maintaining life and optimising productivity in dairy cattle.

However, in contrast to the time given to other nutrients in a dairy cow’s diet, water often receives little attention. In many situations, a cow’s intake can be limited either through supply, quality or accessibility, which could be compromising its potential productivity. This is particularly important during summer when water intakes will increase.

Water requirements

Due to milk production, modern dairy cows have the highest daily requirement for drinking water per unit of body mass of all land-based mammals (Figure 1). A dairy cow requires water for a multitude of functions, including digestion and metabolism of energy and nutrients, transport of nutrients and metabolites to and from cells in the blood, excretion of waste products (via urine, faeces and respiration), maintenance of ion and fluid balance, thermoregulation and creation of a fluid environment within which the foetus develops (Murphy, 1992).

Water requirements are mostly met through water ingested as (free) drinking water and that found in feed, with a very small proportion produced through metabolic oxidation (metabolic water). In lactating dairy cattle, 70% to 97% of daily water intake can come from drinking water, with the variation due to the dry matter content of the diet (Dahlborn et al, 1998).

A cow’s yield is directly related to the amount of water in its body, which ranges between 56% and 81% of its bodyweight. However, this varies with lactation stage as cows in early lactation will have a higher water content than those in later lactation (69% versus 62%). Of a cow’s total daily water intake, approximately 26% to 34% will be “lost” via milk secretion (Holter and Urban, 1992), so for every litre of milk it produces, it will need to drink at least three litres of water.

As well as dry matter content and diet composition, water requirements will also be influenced by yield, lactation stage and ambient temperature, with intakes potentially doubling during periods of heat stress. Based on these variables, a dairy cow will, on average, consume between 115 litres to 190 litres of water per day.

While dry matter content of the diet will influence the proportion of total water intake that comes from drinking water, there is also a direct relationship between dry matter intake and water intake in cattle. If water intake decreases, dry matter intake will also typically decrease. Thus, if water intake is restricted either through supply or quality then intakes will be affected, with subsequent effects on productivity.

Drinking patterns

Dairy cows are suction drinkers – they immerse their lips in water, creating a vacuum in their mouth, then move water to the back of their throat using their tongue. However, initially they will “test” water by “lapping” it before committing to drink. They can drink at rates of 15 litres to 20 litres per minute, with approximately half an hour a day spent drinking or around a water source.

Cows are creatures of habit and peak water intake will usually coincide with end of milking, so this must be considered when planning water supplies. Cows also prefer drinking water temperature to be similar to their body temperature, regardless of the ambient temperature. Plate cooler water or solar energy to heat drinking water are options when considering how to supply warm water.

Source and quality

According to DairyCo figures (2015), the average farm spends £31/cow/year on water; however, on some farms it may be three times this amount. Of all the water used on a farm (plant cleaning, parlour washings and so on) drinking water accounts for 50% to 75%.

While natural water sources may seem a relatively low-cost way of supplying drinking water, cows prefer to drink from troughs and natural water sources also have the potential to introduce or spread disease, as well as lead to disruption of local wildlife habitats.

With the increase in the number of farms using borehole water to reduce costs, it is important to evaluate the water quality. Testing can be carried out relatively easily and identify the level of contaminants present and how these may be influencing cow performance.

Total dissolved solids provides an indication of the total of both the dissolved and suspended inorganic matter in the sample.

High concentrations of dissolved solids – such as sulfate, chloride, iron, manganese and nitrates – can significantly affect dairy cow performance. In particular, high iron levels can result in reduced palatability, immune dysfunction and decrease absorption of copper, manganese and zinc from the diet.

Testing may also indicate whether the water has higher than acceptable levels of bacterial contamination or the presence of toxic compounds such as heavy metals.

Managing troughs

A cow has a sense of smell approximately eight times greater than a human, therefore foul odours or tastes will impact on water intake.

Water can either become contaminated at the source or the point of use – the trough. Water contamination by dust, spilled feed and faecal matter can lead to growth of slime moulds, which will eventually die and decay, tainting the water as well as producing foul odours that will deter cows from drinking (Figure 2). In severe instances, water contamination can lead to spread of disease, with subsequent effects on herd health.

To avoid a build-up of contamination and keep water supply fresh, it is important troughs are regularly cleaned and positioned where they cannot be easily contaminated with faeces. A sign water quality may be suboptimal is cows lapping surface water at troughs, but failing to drink. “Tip over” troughs make regular cleaning easy, as does adding a large bore drain into the bottom of a fixed trough. Large concrete troughs can be more difficult to manage and using goldfish is a common solution; however, sometimes even goldfish can become overwhelmed with the challenge (Figure 3).

To encourage drinking, the height of the water trough is important, with cows preferring to drink at a height of approximately 70cm (this will vary with the size of cow) so troughs should be positioned with their edge 75cm to 85cm off of the floor, with a water level 5cm to 10cm below to reduce splashing and pooling of water around the trough.

Positioning is also critical, with parlour return passageways being a common site. However, due to the high usage these troughs receive, attention must also be paid to the filling rate of the trough to ensure it cannot be drunk dry – a minimum fill rate of 10 litres per minute is recommended. The fill rate should be sufficient such that the water depth never drops below 7.5cm, even during peak usage, to provide cows with sufficient depth to drink.

Crossover passageways are also a popular place for water troughs, but if passageways are too narrow, troughs here can impact on cow flow, as will having troughs in a dead end, which may discourage subordinate cows from drinking. If water troughs are placed in crossover passageways, a minimum width of 3.6m is recommended to allow a cow to drink, plus two cows to pass behind it. Although possible to plan in new buildings, this is rarely present in older sheds. If space allows, though, removing cubicles to expand passageways can achieve adequate width.

To prevent bullying at the water trough it is also important to have sufficient numbers of troughs so subordinate animals cannot be prevented from drinking. At least 10% of the herd must be able to drink at any one time or there should be a minimum of 10cm of trough space for every cow in the herd. It is often thought cows standing in water troughs are cooling their feet; however, this is actually a display of dominance when water supply is short (Figure 4).

On many farms, the importance of clean, fresh and plentiful water is overlooked, leading to detrimental impacts on herd productivity. Since milk comprises 87% water, it is no surprise restriction of water intakes will impact on milk yields. This is even more important in summer, with potential for heat stress to exacerbate any shortcomings in a herd’s water supply.