Salt for Swine

Studies at Wisconsin and Purdue showed that a deficiency of salt decreased daily gain and feed efficiency in the pig (6, 78). They also showed that salt supplies sodium and chloride in about the proper proportions for growing pigs (6). The salt-deficient pigs licked their cages looking for salt.

Four studies at Purdue showed that pigs receiving no salt in their diet required 174 pounds more feed per 100 pounds of gain; their rate of gain was only half as fast as that of pigs given adequate salt (3). In this trial, one pound of salt saved 287 pounds of feed. Furthermore, the pigs deficient in salt ate 12.5 times as much of the mineral mixture as the pigs fed salt. This reflected the craving for something they could not get except in common salt. Table 6 shows one year’s data (1945).

Lot

How Salt Was Fed

Average Final Weight of Hogs, lb (85 day trial)

Average Daily Gain, lb

Feed per 100 lb of Gain, lb

Feed Cost Per 100 lb Gain

No salt fed

174

0.99

Corn 451.0
Supplement 100.7
Mineral 17.0
Total feed 568.7

$12.53

Loose salt fed, but none in the mineral mixture

255

1.94

Corn 321.4
Supplement 73.1
Mineral 0.7
Total feed 395.2

$8.68

In another trial at Purdue, the salt-fed pigs ate 23% more feed and gained at nearly double the rate on 33% less feed (3). One pound of salt saved 185 pounds of feed.

A study at Purdue showed that corn-soybean meal diets were improved by the addition of 0.2% salt (4). Pigs fed no salt showed a lower rate of gain and reduced feed utilization.

The 1998 National Research Council Swine Nutrient Requirements Committee recommends, "…that 0.20% to 0.25% added sodium chloride will meet dietary sodium and chloride requirements of growing-finishing pigs fed a corn-soybean meal diet" (277). Studies at Purdue (74, 75) serve as the basis for this recommendation. This is similar to the European ARC which recommends a level of 0.33% salt in the diet for the growing pig (124). However, recent research with the early weaned pig suggests that the sodium and chloride requirement maybe higher (272). Pigs weaned at 21 days of age required .40% salt for maximum performance through five weeks of age. During this time the gain:feed ratio was greater than 0.5:1, so that a nutrient dense diet is required for optimum performance.

The sodium and chloride requirements of breeding swine are not well established. Results of one study (123) showed that diets containing 0.3% salt were deficient for pregnant sows. A 1989 regional university study (Clemson, Florida, Georgia, Kentucky, Oklahoma, Texas and Virginia) evaluated adding 0.25% vs 0.5% salt to a corn-soy diet for sows through three parities (litters). The sows fed 0.5% supplemental salt resulted in a small increase in pigs farrowed, live pigs at birth, pigs weaned, birth weights and weaning weights. The authors concluded, "when continued for more than one reproductive cycle, feeding less than 0.5% salt appears to reduce litter size at birth and weaning" (150).

University of Alberta studies showed no harmful effect when salt was added to the drinking water of growing-finishing pigs at a level of 5,000 ppm (5). These and other studies indicate it is extremely difficult to salt-poison pigs when salt is added to the diet and the pigs are allowed free access to water.

In order to poison pigs with salt, the Wisconsin Station salt-starved the pigs for several months (7). They fed the pigs swill containing salt in a crowded trough space with no water available. Salt in the swill totaled 1.5% to 2.0% (wet basis) or 6% to 8% on a dry matter basis. It required more than one day of excessive salt feeding before symptoms of poisoning became evident. If water had been available, the pigs might have drunk enough to satisfactorily dilute the salt content of their digestive tract and body tissues.

In USDA studies, pigs were fed levels of salt of 0%, 1%, 2%, 4%, 8%, and 12% of the diet (8). The average daily gain for the pigs fed 2% salt exceeded those of the other pigs. Increasing levels of salt above 2% decreased gain and feed efficiency. The pigs on 12% salt ate enough feed to give them an intake of about one half pound of salt daily. One pig on the 8% salt level showed symptoms of possible salt poisoning, In another USDA trial, one pig weighing 218 pounds, after being fed 26 days on a high-salt diet, consistently consumed an average of 8.4 pounds of total diet and 1.1 pounds of salt daily. A daily water intake of 2.35 gallons was apparently sufficient to permit elimination of the salt without ill effects (8). The important fact is that swine are very resistant to salt poisoning as long as adequate water is available.

Manure disposal is an important consideration for many large swine confinement units. A Purdue study involved feeding pigs 0.2% versus 0.5% salt in the diet (73). Application of 40 tons of swine waste (10,000) gallons per acre per year resulted in maximum corn yields. Exchangeable soil sodium concentration increased from the swine waste application; however, the sodium accumulation (at both levels of salt in the diet) was not high enough to cause any problem with soil productivity. These data are interpreted to show that feeding the recommended salt concentrations should not limit the soil application of swine manure.