Salt has been recognized quite early in human history as a valuable ingredient. Its importance was signified by the fact that salt was used as a form of payment in antiquity. Today, salt is quite inexpensive and readily available throughout the world. Its significance in nutrition remains unchanged, although not many think of it when formulating diets for animals.
Indeed, the golden rule of thumb has been to add 0.5 percent salt in all types of pig and poultry formulas, and this has served the feed industry quite well for many decades. This rule is still valid, but current knowledge has brought up the need for certain clarifications and exceptions.
Sodium and chlorine
Salt is used to cover the animal requirements for sodium (Na) and chlorine (Cl). According to the National Research Council, these requirements range from about 0.10 to 0.25 percent in complete feed for most classes of poultry and pigs. Assuming (pure) salt contains 39.5 percent Na and 60.5 percent Cl, then adding 0.5 percent salt in a diet provides about 0.20 percent Na and 0.30 percent Cl. It is evident, therefore, that the 0.5 percent salt rule of thumb was created to ensure diets contain enough sodium. The extra chlorine is being excreted through urination.
Very briefly, sodium and chlorine are major electrolytes that contribute to the maintenance of cellular membrane electrochemical gradient (known as membrane potential). They are also involved in the digestion (HCl in the stomach), absorption (Na) and transportation of nutrients from the intestines into the blood stream. They also contribute to the maintenance of blood volume and pressure, and they participate in the renin-angiotensin-aldosterone system. It is apparent from this impressive list of functions that sodium and chlorine are absolutely vital for the organism and life itself.
Severe deficiency of sodium and chloride leads to cerebral edema, seizures, coma, brain damage and eventually death. A mild deficiency of sodium and chloride is evident in the form of loss of productivity in all classes of animals. Today, a deficiency in sodium and chloride is possible only when there is an error during mixing of feed or during formulation. This is not as rare as one might imagine as such errors happen without noticing until it is too late. In most cases, it is a matter of not adding enough salt, which then leads to suboptimal productivity and loss of profit.
A mild deficiency of sodium and chloride is evident in the form of loss of productivity in all classes of animals.
On the other hand, animals can tolerate quite high concentrations of salt in their diets. Studies have demonstrated that growing pigs can tolerate up to 8 percent salt in their diets (that is 40 times higher than the required level). But to cope with such high levels of salt, and keep growing, they require ample quantities of non-saline water. Otherwise, with limited water supply or with saline water, pigs cannot tolerate even 1 percent salt in their diets (that is twice their requirement). Poultry are not so flexible in their salt tolerance, especially layers as it affects their egg quality.
In many regions of the world, the only available water supply for consumption by animals is saline. Coastal water may contain up to 200 mg/L Na, or even more in some extreme cases. In such cases, this fact must be taken into account when formulating diets. This is done by reducing proportionately the salt in feed and (or) avoiding ingredients rich in salt (for example, fishmeal, whey, blood products, etc.). Otherwise, animals enter into a futile circle of trying to detoxify excess salt by using saline water, only making salt toxicity a chronic, subclinical condition. In mild cases, a mild diarrhea may appear and remain persistent as long as the problem continues due to a disruption of the anion-cation balance. In severe cases, salt poisoning ensues, tantamount to trying to quench your thirst by drinking sea water.
Newly-born or hatched animals offered diets rich in sodium and chlorine may be at risk of salt toxicity if they do not know how to operate drinkers. To this end, cup drinkers usually offer an advantage over nipple-type drinkers. Otherwise, letting nipples dribble for the first couple days will ensure animals recognize the source of water.
Assuming a mild salt toxicosis can be avoided (as described above), salt can be a very inexpensive growth-promoting additive in diets for all classes of animals as it improves palatability. Of course, where animals are predisposed to diarrheas, excess salt will contribute to soft stools, which if not of pathological origin should not hamper growth and productivity.
Feeding sufficient salt to breeding animals is important to satisfy the needs of limit-fed gestating sows and enhance palatability of feed for lactating sows. In contrast, layers should be fed enough salt to cover the Cl needs, and then, an additional source of Na, free of Cl, to meet their Na requirements.
Ingredients rich in sodium and chloride are fishmeal, whey and derivatives, and blood products. In fact, the combination of these ingredients in expensive diets usually exceeds requirements for sodium and chlorine. This makes it essential for young animals (piglets and broilers) to have access to non-saline water when fed diets based on such ingredients. In fact, when saline water is the only source of water available, such ingredients should be avoided completely.
Plasma may contain up to 5 percent Na and 2 percent Cl, whereas fishmeal contains no more than 1 percent of each nutrient. Similarly, meat meal contains about the same concentration of salt as fish meal, and this should be taken into consideration where this ingredient is allowed in animal diets. On the other hand, another commonly used ingredient (nowadays even in early broiler superstarter feeds), whey contains about 1 percent Na and 1.5 percent Cl. Delactosed whey (mainly a protein source) and other whey products (mainly lactose) contain even higher levels depending on the degree of protein and ash concentration achieved during the removal of components.
Salt remains a very significant ingredient because sodium and chlorine are vital for life and productivity. Salt is the cheapest available source for these two nutrients. For areas suffering from lack of non-saline water, the issue of salt in animal diets is an important one. A correct balance of salt intake through water and feed can enhance productivity and reduce diarrheas.