The low-down on salt intake

Estimated reading time: 6 minutes

• Salt, consisting of 40% sodium and 60% chloride, is essential for the nervous system, muscle function, and maintaining water-mineral balance in animals.
• Ruminants require more salt during hot weather due to sweating, and salt supplements, often combined with phosphorus, are necessary for optimal health and production.
• Signs of salt deficiency in livestock include licking stones or other objects and ingesting soil, while symptoms of salt poisoning include nervousness, diarrhoea, blindness, and, in extreme cases, death.
• Chloride intake supports metabolic functions like osmotic pressure, blood pH balance, and carbon dioxide transport, with deficiencies leading to reduced feed and water intake and excesses causing dehydration and kidney issues.
• The amount and type of salt in livestock licks can influence intake, and urea-based licks should be introduced gradually to prevent urea poisoning or alkalosis in ruminants.

Salt, or sodium chloride (NaCI), consists of 40% sodium and 60% chloride, and is widely regarded as a key nutrient necessary for the normal functioning of mammals.

In addition to regulating the natural water balance in the internal biome of humans and animals, the body needs small amounts of sodium to send signals through the nervous system, promote muscle movement, maintain an optimal water-mineral balance (electrolyte balance), and regulate blood pressure. Sodium also plays a role in transporting glucose, which supplies energy to cells, through the cell membrane into the cell.

Stockfarm spoke with two specialists in the field of livestock nutrition about salt’s action and metabolic function in an animal’s body, signs of deficiencies or excessive intake, the correct amount of salt-containing lick to rectify deficiencies, obstacles that can impair the absorption of salt, and the like.

Deficiencies and excesses

Mature cows require approximately 30g of salt and 10g of phosphate daily; a sheep’s salt requirement is around 9g/day. Lick is aimed at supplementing deficiencies in animals’ nutrition and improving their health and production. “The salt that a ruminant requires is mainly influenced by the condition of both veld and the animals,” says Dr Klaas-Jan Leeuw, researcher in ruminant nutrition at the Agricultural Research Council (ARC) in Irene.

“Ruminants typically require more salt in summer due to the fact that they excrete salt when they sweat. Salt phosphate licks, in addition to phosphorus supplementation, are therefore essential for meeting their salt requirements.”

Salt supplements are affordable, and animals usually only ingest what they need. The amount of salt a lick contains will also determine the amount the animal consumes. Any salt the animal consumes in excess is excreted by the kidneys via the urine, provided that enough fresh, clean drinking water is available so the body can excrete this excess. In the case of highly saline drinking water, the supply of salt licks should be limited or it should not be given at all. Water’s salt content should preferably be below 0,5% (anything exceeding 1,5% may be toxic to ruminants).

Ruminants have a high salt tolerance, and symptoms such as blindness, intense nervousness, diarrhoea, and eventual collapse and death (as was the case with two sheep, which were part of a study, that consumed excessive amounts of salt) can be indicative of salt poisoning. This will not occur under practical conditions. In cattle this can manifest as suppressed appetite, less water consumed and therefore less milk produced, less saliva from the mouth, vomiting, diarrhoea, walking in circles, aggression, blindness, and partial paralysis. If salt poisoning is suspected, it is advisable to consult a veterinarian.

Recognise salt deficiencies

In the event of a salt deficiency, animals may begin licking objects such as stones and iron pipes or poles, ingest soil and tree bark, or drink urine. Dr Leeuw says animals that experience salt deficiency require more magnesium and calcium – something that can have far-reaching consequences for an animal’s health.

Chloride intake is another key factor, as it controls metabolic functions such as osmotic pressure in the body, regulates electrolytes and blood oxygen levels, transports carbon dioxide, and maintains the pH of the stomach acid. A chloride deficiency may slow down breathing, cause lethargy and constipation and, more specifically, lead to lower feed and water intake and, ultimately, subpar production.

“Fortunately, chloride deficiencies are rare,” says Dr Leeuw. “An excess of chloride, on the other hand, can make the blood more acidic, leading to dehydration and kidney issues due to the excess chloride that must be excreted. This is typically the case in animals that do not drink enough water. The accumulation of chloride may cause kidney damage due to a drop in the pH level. In this case, enough clean and fresh water must be available immediately.”

Accuracy and effectiveness

Dr Ockert Einkamerer, a senior lecturer in Animal Science at the University of the Free State, says the amount of salt in cattle licks, in addition to the sodium and chloride they contain, will mainly determine the amount of lick ingested.

Note that the type of lick and the raw materials included in the mix – for example a mineral (phosphate lick), or production or protein lick (winter lick) – can also affect cattle’s lick intake (Table 1). More maize, molasses or oilcake meal, and even wheat bran or hominy chop, can affect the intake of these licks at the same level of salt inclusion.

Table 1: Percentage of salt inclusion in a phosphate lick and quantity (gram) a mature animal consumes (rule of thumb) daily.

Salt licks, or rock salt, should be a standard feature in livestock camps, says Dr Einkamerer. “The availability of urea-containing licks can even lead to salt hunger. A salt hungry mature animal may very well ingest enough urea along with the lick, to cause alkalosis or urea poisoning.

“The recommended intake of urea for sheep is 7 to 8g/day, and cattle 50 to 80g/day. Both species can ingest more per day, but this should happen gradually during the day and only if the animals are adapted, and if the lick contains enough grain and molasses. As little as 4g/sheep or 15 to 20g/cattle ingested at a time could lead to this metabolic disturbance. Ruminants must therefore be adapted before they are given urea-based licks.”

Impact on health

The recommended salt inclusion in complete rations for sheep, goats or cattle ranges between 0,25 and 0,5% of the total diet. It rarely exceeds 0,5%. As much as 0,75% can be included, but anything higher may lead to reduced voluntary intake in ruminants or adversely affect their health. To date little research has been done on the latter and only international information is available in this regard.

“Nor is there much information about the source or fineness of the salt given to animals. It is important to consider that different sources may contain other macro- or microminerals. Not only that, but finer salt is often more expensive than coarse salt. Fine salt is preferable for complete rations, as it is easy to mix with less clumping occurring.

“It is probably better to pellet feeds using fine salt,” says Dr Einkamerer. “Fine salt can, however, be difficult to work with, because salt is generally hygroscopic, which means it ‘attacks’ water and makes it less fluid. The cost of fine salt will probably be a deciding factor in using it or not.”

For more information, contact Dr Klaas-Jan Leeuw on 072 567 4089 or kleeuw@arc.agric.za, or Dr Ockert Einkamerer on 051 401 2389 or einkamererob@ufs.ac.za. – Carin Venter, Plaas Media