Salt for Sheep

Sheep deficient in salt develop a craving for it. Like cattle, they may lick and chew wood, dirt, rocks and other materials. They may also consume toxic amounts of poisonous plants (155). These are manifestations of an unsatisfied craving for salt. In sheep, inadequate salt intake results in decreased feed consumption and decreased efficiency of nutrient utilization. Eventually, milk production, wool production and reproduction rate decline. A very severe deficiency may cause death.

Feed costs are the greatest single expense in sheep production. A number of early experiments at Kansas, Iowa and elsewhere showed that adding salt to sheep diets reduces feed costs. A 1953 California study showed that adding salt to an alfalfa-barley diet increased rate of gain and feed efficiency (27). An Australian study showed that salt supplementation increased wool growth (68).

The use of salt blocks or salt stations can be used to distribute sheep over a range area in the same manner as previously discussed in the beef cattle section.

In a California study, ewes were fed diets with sodium chloride contents of 0.5%, 4.8%, and 9.1% for 253 days during growth, finishing, breeding, gestation and early lactation (26). These levels of salt did not cause any differences in performance during growth, finishing, breeding or gestation. The findings are shown in Table 4. However, the 13.1% salt level did cause more weight loss during lactation and somewhat decreased the number of lambs raised. None of the salt levels affected the gain of the lambs, blood hematocrits, serum albumin and sodium, or milk protein, sodium or potassium. The blood and milk chlorides were increased, however, at the high salt levels.

Australian researchers have shown that salt intake prior to harvest may influence dehydration associated with shipment from the farm to the processing plant. Lambs consuming a high-salt diet based on saltbush had significantly higher muscle water content than lambs fed a low salt diet (321).

Items Compared	Lot 1 0.5% NaCl	Lot 2 4.8% NaCl	Lot 3 9.1% NaCl	Lot 4 13.1% NaCl
Ewes per lot	10	10	10	10
Average initial weight, lb	70	68	74	70
Average final weight, lb	102	104	105	104
Average daily gain, lb	0.47	0.52	0.45	0.48
Average daily feed, basal ration	4.1	4.1	4.1	3.9
NaCl, lb intake daily	--	0.20	0.37	0.58
Basal ration per 100 lb of gain, lb	884	790	842	812
Average daily water intake, lb	14.7	25.4	32.6	45.8
Average water intake per gram of added NaCl, ml	--	54.9	52	56.5

The maximum amount of salt sheep can bear depends on the dissolved solids in the water and mineral concentrations in the feed. For example, tolerance of sheep to drinking water containing 1.3% sodium chloride was remarkably good, according to Australian workers (29) when the diet had normal sodium concentrations. Productivity, in terms of body weight and wool production, was unaffected by prolonged drinking (15 months or more) of solutions with such a salt level. The use of water with 1.3% salt instead of fresh water resulted in greater voluntary intakes of water and, consequently, a greater flow of fluid through the rumen.

Other Australian studies show that 1.0% and 1.3% salt in the water may occasionally have detrimental effects (66, 67). These differences in response are due to differences in the sodium and chloride contents of the pasture. Wilson suggested that sheep in Australia entirely dependent on salt bush, should have no more than 0.6% sodium chloride (6,000 ppm) in the drinking water (69).

A California study showed that sodium chloride levels of 0.66%, 4.8%, 9.4% and 12.8% in the diet (or daily intakes of 0.03, 0.16, 0.33 and 0.46 pounds of salt) fed to growing and finishing sheep had no detectable influence on nitrogen digestibility, nitrogen retention or total digestible nutrient content of the diet (12). The high salt intakes were not detrimental to efficiency of feed utilization or average daily gain. In another California study, nitrogen digestibility and nitrogen retention were increased with high salt levels of 5.2%, 9.5% and 13.7% in the diet (27). Australian researchers found that increasing salt levels from 0 to 8% reduced diet digestibility from 59.1 to 57.3% in sheep (316). Thus, it appears that these high levels of salt have little or no harmful effect on diet digestibility with sheep, provided they have plenty of water to drink.

A great deal of work has shown that salt can be added to protein supplements to limit their intake when they are self-fed to sheep. The results obtained are similar to those discussed in the beef cattle section. Such mixtures usually contain from 10% to 50% salt (155).

Formation of calculi (stones or crystals) within the urinary tract of sheep is a common disease that can be minimized by feeding extra salt. The most common calculi found in lambs is the struvite type, which contains calcium, magnesium and ammonium phosphates. The mineral composition of drinking water, in conjunction with mineral imbalances in the diet, probably contributes more to the initiation of calculi formation than does the lack of water itself. Wethers with calculi have abdominal discomfort as indicated by restless, kicking at their belly and make frequent attempts to urinate. Attempts to urinate are often accompanied by rapid twitching of the tail. Animals may also groan or bleat while attempting to urinate.

Prevention of this condition is much easier and more effective than attempts at treatment. The following are offered for consideration in the development of a urinary calculi prevention program. First, delay castration of young lambs as long as possible. Second, clean, cool water is a must. The diet should contain a 2:1 calcium to phosphorus ratio. In a flock where lambs have been diagnosed with urinary calculi, adding of 3-4% salt in the ration stimulates water intake, dilutes the mineral concentration in the urine, and helps to reduce the incidence in the rest of the flock. Finally, ammonium chloride should be added to the feed at the rate of 0.5-1.5% of the diet to prevent stone formation (291).

A 1975 Purdue study showed that the dietary salt requirements for growing lambs ranged between 0.33% and 0.43% of the air-dry (90% dry matter) (65). The 1985 National Research Council sheep publications state, "In mixed feeds, it is customary to add 0.5% salt to the complete diet or 1.0% to the concentrate portion" (155). The NRC gave a requirement for salt as a range of 0.23% to 0.46% NaCl in the diet dry matter. It also indicates that 9% salt in the diet should be the maximum tolerable level used.

Because blood sodium, potassium and chloride are important in regulating water and electrolyte balance and the humoral immune response, pre-stress salt levels may be important in determining post-stress recovery. Cole (273) reported that sodium chloride content of lamb diets prior to feed and water deprivation affected post-deprivation sodium and potassium status. These data suggest that adding 4 grams of salt per day to the diet of feeder lambs may be important in decreasing the adverse effects of marketing and transport stress and thereby improve subsequent animal health and performance.