Salt in dry sow diets

Increasing the salt level in the diet is a simple and effective strategy to help with the control of discharging sow syndrome and urinary tract infections.

Discharging sow syndrome

The discharging sow syndrome and ascending urinary tract infection in breeder units are often an ongoing problem. The classic signs include purulent vulval discharge from sows following mating, pus and blood in the urine, poor conception, small litters and even death. On post mortem these dead sows show the classic signs of ascending urinary tract infection. The bladder is inflamed (cystitis), the ureters or tubes leading from the kidneys to the bladder are thickened and inflamed (uretitis) and the kidneys contain pockets of pus (pyelonephritis).

These diseases are very costly for two reasons. Firstly, reproductive rate drops dramatically and secondly, the control and treatment measures necessary take time and money. These measures consist of improving the hygiene, identification of the causative organisms and medication with the antibiotic of choice, while acidification of the diet can also be considered, as this alters the urine's pH.

Reducing the problem

Frequently the organisms causing the problem are those normally found in the piggery environment. When a problem occurs this is an indication that the number of bacteria or the challenge placed on the animal's urinary and reproductive tracts is too great for the body's normal defence mechanisms. These organisms may enter these parts of the sow either during the mating process or by natural invasion of the urinary tract. The vulva is particularly vulnerable to invasion because of its shape and its exposure to the population of bacteria within the piggery environment. To reduce the problem it is necessary to reduce the number of bacteria. Some options include:

  • regular flushing of the kidneys, ureters, bladders and also the boars' sheath areas, by natural means. This is best achieved by increasing water intake so that the frequency of urination is also increased.
  • culling dog-sitter sows whose vulvas have high exposure to contaminants
  • improving hygiene, such as floor slopes, width between slats, cleaning methods and frequency
  • using artificial breeding to break the disease cycle, as a lower priority option for control, if natural conception with boars is suspected to be responsible for infecting sows during mating.

Increasing water intake

Feed stimuli

Boars and sows should be encouraged to drink more and hence stimulate urination. Large animals, in particular those in stalls, generally are reluctant to stand up once they have been fed in the morning. This leads to infrequent water intake and urination predisposing the sow's bladder and boar's sheath to accumulated bacteria and greater risk of discharging sow syndrome. Feeding dry sows twice or even three times per day, although an added chore, and the passage through the dry sow shed with a feed trolley or the light scattering of feed in front of the sows, is often enough stimulus for them to get up and increase their water intake.

Increased salt intake

The addition of salt in the diet at 1% (the standard recommendation is 0.25% for growers, to 0.50% for sows) stimulates the brain's thirst centre and encourages sows to stand and promotes drinking and urination. It is important to first check on the diet's current salt inclusion rate. Then try a level of 0.5% salt first. Salt is cheap and its inclusion at even 1% of the dry sow diet is worth investigating as a part of the strategy in the control of discharging sow syndrome and urinary tract infections.

Most local producers who have adopted this practice of higher salt levels for sows have been pleased with the results. However, where problems still exist, it appears to be confined mainly to young females.

Case study

In one particular field case the dietary salt level had fallen well below the base recommended minimum of 0.25%. The figure was never checked and was presumed to be adequate. Salt is not toxic at 1% of the diet provided adequate good quality water is freely available (1% = 10 kg per tonne of feed). The level of salt in the diet on the farm was adjusted to 1% and the other steps outlined to encourage an increase in the frequency of drinking and urination were adopted. The immediate signs were a change in the colour of the urine, turning from a dark yellow to a clear flow. Conception rates improved dramatically and the need for medication was abandoned as clinical evidence of the disease disappeared. The increase in litter sizes on top of the improving conception rates created an embarrassing position as the herd had increased in sow numbers to compensate for the drop in reproduction.

Female replacements

During the grower/finisher phase most gilts are reared in separate pens to their male counterparts and so are never mated prior to entering the herd as a female replacement. Therefore the most likely cause of reproductive/urinary tract infection in gilts is the migration of organisms from the environment up the urinary tract.

When keeping female replacements, levels of salt up to 0.5% of the diet is encouraged. A higher urinary output reduces the chance of common organisms entering the reproductive/urinary system.