Managing water quality during dry times

Bonnie Skinner, Manager Biosecurity & Extension, New South Wales

Supplying livestock with good quality drinking water through hot dry summers is vital to maintain health and productivity and forms part of good biosecurity practices. Some of the main water quality concerns of producers during extended hot dry periods should be salinity, algal growth, and contamination of water by manure and other pollutants.

Water intake during summer

As ambient temperatures rise so to do water requirements of livestock. Table 1 describes daily water requirements of various livestock. Water consumption by sheep and cattle can increase by anywhere between 40-80% in the summer months[1].

In summer, livestock consume large amounts of highly fibrous, less digestible feed when on pasture or when being hand fed hay and grains. More water must therefore be consumed in order to break this roughage down effectively in the rumen. Stock grazing saltbush or fed supplementary salt will also require more water than average.

Livestock also experience greater losses of bodily fluids through increased sweating and respiration (i.e. panting) in an effort to keep cool.  Ensuring that livestock have adequate access to shade and do not have to travel more than 3km (sheep) or 5km (cattle) to a watering point will help manage these losses.

Stock type

Consumption per head per day (L)
Sheep
Dry sheep
Grassland 2-6
Saltbush 4-12
Ewes with lambs 4-10
Weaners 2-4
Cattle
Dry stock (400kg) 35-80
Young stock 25-50
Lactating cows
Grassland 40-100
Saltbush 70-140
Horses 40-50

Right: Table 1 Average daily water requirements of stock

Adapted from Water Requirements for Sheep and Cattle, NSW DPI (2014)
Note: consumption may vary depending on livestock breed and class, seasonal conditions, water and feed quality

Salinity

During prolonged hot weather evaporation can greatly increase the salinity of water in troughs and dams. Dams can evaporate anywhere from 1–2.5 metres during the course of a year. Livestock can tolerate saline water to certain concentrations when introduced slowly however sudden marked increases may cause stock to refuse to drink it or cause toxic effects. Table 2 shows maximum salinity tolerance of various classes of livestock.

Where stock are consuming large amounts of salt in their diet (e.g. salt bush) tolerance to saline water may be reduced, or the toxic effects of salt compounded if adequate fresh water is not supplied. Mortalities of sheep and cattle have been reported from drinking saline bore water which was concentrated due to evaporation in troughs[2]. There have also been findings of salt toxicity in cattle caused by saline dam concentrated due to evaporation[3].

Clinical signs of salt poisoning tend to be evident in large proportions of the herd and include excessive thirst, abdominal pain and diarrhoea. As the condition progresses nervous signs such as muscle tremors and convulsions can be observed, often followed by coma and death.

Water should be tested and monitored monthly for salinity during summer and particularly during drought.  To manage salinity levels water troughs should be flushed and scrubbed as frequently as practical; once to twice weekly is ideal.

Table 2 Tolerances of livestock to Total Dissolved Solids (salinity) in drinking watera

Total dissolved solids (mg/L)
Livestock No adverse effects on animals expected Animals may have an initial reluctance to drink or scour but should adapt without loss of production  Loss of production and decline in animal health/condition expected. Stock may tolerate these levels for short periods if introduced gradually
Sheep 0-5,000 5000-10,000 10,000 – 13,000b
Beef cattle 0-2,500 2,500-4,000 5,000-10,000
Dairy cattle 0-2,500 2,500-4,000 4,000-7,000
Horses 0-4,000 4,000-6,000 6,000-8,000

a Adapted from Australian and New Zealand Guidelines for Fresh and Marine Water Quality (2000)
b Sheep on lush green feed may tolerate up to 13 000 mg/L TDS without loss of condition or production

Algae

Algae occurs naturally in troughs and dams. Algal blooms (excessive growth of algae species) are common in summer in still or slow-flowing water when temperatures are warm and water is abundant with nutrients.

Build-up of algae in water reduces its palatability and can block water pipes and outlets. Some types of algae are toxic to stock, the most notable of which is blue-green algae. Blue-green algae is seen on the surface of the water as a paint-like green scum with a musty odour. Blue-green alagae occurs most commonly in late summer and early autumn and in drought conditions. It can produce toxins which affect the liver (hepatotoxins) and toxins which affect the nervous system (neurotoxins). Stock that have consumed the toxins can show clinical signs in as little as 15-30 minutes depending on the quantity and concentration of toxins consumed. These signs may include weakness, trembling and staggering progressing to prolonged recumbency and death within 24 hours. Animals that survive the acute poisoning will generally have sustained severe liver damage and also show signs of jaundice and photosensitisation. Where blue-green algae is suspected stock should be removed from the water source immediately and further investigation undertaken.

Water troughs should be cleaned regularly to prevent algal build-up. Shading troughs where possible and ensuring tanks are fitted with covers will help to reduce the amount of sunlight. Chemical control is dependent on the type of water being treated and may include simazine, chelated copper or copper sulphate. Chemical treatment of blue-green algae will cause toxins to be released and so stock must be kept off for the length of the withholding period or 14 days, whichever is longer. Some water sources may not be treatable with chemicals or require special permissions- consult your relevant state or territory authority for further information.

Contamination with pollutants and pathogens

Shrinking dams where livestock are forced to wade in deeper for water often causes the edges of a dam to become muddy and boggy. Agitated soil and manure in the water reduces its palatability. Warm shallow water can also act as a perfect reservoir for a number bacteria which accumulate due to manure and vegetated material blown into dams and can be transmitted by water. These bacteria can be particularly harmful to young or weak stock and can reduce animal production. Some pathogens of concern include e.coli, salmonella, leptospira (leptospirosis), clostridium botulinum (botulism). Consideration should be made to reticulating from dams into troughs and fencing off dam areas if possible. Fencing off the windward side of the dam with closed wire fencing may help to trap blown dry vegetation from entering the dam.

 

For more information on the topics discussed above, please contact your LBN state manager.

 

[1]

National Research Council (2000). Nutrient requirements of beef cattle. Washington, DC: National Academy of Sciences; Department of Primary Industries NSW (2014). Water requirements for sheep and cattle (3 ed.) (No. 326). Primefacts. Retrieved from: https://www.dpi.nsw.gov.au/__data/assets/pdf_file/0009/96273/Water-requirements-for-sheep-and-cattle.pdf

[2]

Moule GR. (1945). Salt poisoning of sheep following evaporation of saline waters. Australian Veterinary Journal (21), 37; Ohman, AFS. (1939). Poisoning of cattle by saline bore water. Australian Veterinary Journal (15), 37.

[3]

Ison, S. (2015). Salt poisoning in cattle. Flock and Herd. Retrieved from www.flockandherd.net.au/cattle/reader/salt-poisoning-cattle.html