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Sodium Nutrition of Livestock and Poultry

by Larry L. Berger, Ph.D.
Professor, Animal Sciences
University of Illinois

Animal nutritionists have recognized sodium as an essential nutrient for hundreds of years. Sodium is unique in that animals have a greater appetite for salt than the other nutrients.

Even though the body only contains about 0.2% sodium, it is essential for life and is highly regulated. About half of the sodium in the body is in the soft tissues, and half in bone. Sodium makes up 93% of the basic mineral elements in the blood serum and is the chief cation regulating blood pH. Muscle contraction is dependent on proper sodium concentrations. Sodium plays an essential role in nerve impulse transmission and the rhythmic maintenance of heart action. Efficient absorption of amino acids and monosaccharides from the small intestine also requires adequate sodium.

Producers of confined livestock and poultry often consider lowering the salt concentration in animal diets to reduce sodium and chloride levels in manure to maximize manure application rates. Owners of grazing livestock, trying to reduce costs, sometimes question the need for salt supplementation. The purpose of this article is to review recent research demonstrating the essentiality of sodium supplementation for optimal performance. In addition, new information on disease or management problems associated with suboptimal sodium nutrition will be discussed.

In a recent review, Chiy and Phillips (1995) identified four conditions where sodium deficiency is most likely: 1) Lactating livestock which have high sodium losses in the milk; 2) Rapidly growing livestock and poultry with high sodium retention; 3) Grazing animals under heat stress conditions where forage sodium concentrations are low and there are large losses in sweat; and 4) Animals grazing fertilized pastures where potassium levels are high and sodium is low.

Lactating Animals:

Whitlock et al. (1975) reported a classic example of sodium deficiency in lactating Holstein cows. All salt was removed from the diet, but the cows consumed the equivalent of 10-15 grams of salt per day in the water. The first signs of sodium deficiency were that cows showed excessive urination and consumed approximately 80 liters of water daily under thermal neutral conditions. During the first year, milk production dropped 40% on average for the 45 cow herd. Cows also exhibited pica in that they would eat urine saturated bedding in preference to hay. Reduced feed intake and loss of body condition were common for all cows. Although not observed in this trial, terminal symptoms of a sodium deficiency include shivering, incoordination, weakness, cardiac arrythmia and eventually death.

When cows in this experiment were fed 60 grams of salt per day, urine output gradually decreased, and milk production increased over the next 10 days. During this time salivary sodium and chloride concentrations increased while potassium decreased. Plasma sodium and chloride concentrations followed a similar pattern, but potassium was relatively constant.

Symptoms of a sodium deficiency may often be confused with disease or other nutrient deficiencies. In ruminants, the ratio of sodium to potassium in parotid saliva is the most reliable method of diagnosing a sodium deficiency (Murphy and Connel, 1970). The total sodium plus potassium concentration in parotid saliva is normally around 150 to 180 millimoles per liter in cattle and sheep, respectively. As sodium becomes deficient the animal attempts to maintain ionic strength by increasing potassium levels. As sodium deficiency increases, replacement with potassium begins to lag and ionic strength may drop as much as a 20% (Davison et al. 1980). Sodium supplementation increases milk production in both lactating dairy cows (Davison et al., 1980) and beef cows (Morris and Murphy, 1972; Murphy and Connell, 1970) when the parotid saliva has a sodium:potassium ratio of 5 or less. Sodium:potassium ratios of 17:1 to 25:1 are considered normal, but a deficiency should be suspected if the ratio in saliva decreases below 15:1.

Cromwell et al. (1989) conducted a recent trial using less severe sodium restrictions with gestating and lactating sows. When data from 1,020 litters at eight different research stations were compared, sows fed less than 0.5% salt (0.2% sodium) had reduced litter size 2% to 4% at birth and weaning. In these studies, salt levels were reduced form 0.5% to 0.25% or 0.125%. Although the sows themselves did not show deficiency symptoms, reproductive efficiency was reduced.

Rapid Growth:

As livestock and poultry are selected for faster growth rates sodium requirements may increase because of increased lean deposition and the fact that leaner animals often require less feed per unit of weight gain. As the feed per unit of gain decreases, the concentration of nutrients like sodium, must increase to allow maximum performance.

Researchers at the University of Georgia recently conducted a classical experiment demonstrating this principle with broilers (Britton, 1990). Based on previous research with less highly selected broilers, the sodium requirement for chicks was estimated to be 0.15% (National Research Council, 1984). However, using a typical corn-soy diet, Britton showed that the sodium requirement for maximum growth was at least 0.45% during the first 18 days. With feed efficiencies of less than two pounds of feed per pound of weight gain, these data demonstrate the need for increasing the sodium concentration in the diet. These birds, with very high growth potential, were weighing nearly a pound at 18 days of age.

Additional research with broilers selected for rapid growth shows that feeding sodium deficient diets not only impairs weight gain, but also increases susceptibility to disease. Pimentel and Cook (1987) showed that broilers fed 0.14% sodium in a corn-soy diet had immunosuppression. When broilers were exposed to sheep red blood cells, maximum immune response occurred at sodium concentrations of 0.24% or greater. Broiler salt intake is often minimized to decrease water intake and thus fecal moisture. However, poultry producers must recognize that this perceived benefit should be balanced against increased costs resulting from slower growth and the immunosuppression that may result.

Grazing Animals Under Heat Stress:

Heat stress increases sodium requirements due to sweating and often decreases feed intake. This combination of factors can aggravate a moderate sodium deficiency. For example, McDowell et al. (1983) reported a severe sodium deficiency in cattle on 10 Columbian ranches not providing supplemental salt. The most common outward symptoms were reduced productivity and a brittle dry hair coat.

Infertility is one of the common problems of heat stressed cattle grazing poor quality pastures. Recent research (Arya and Jain, 1986) suggest that adequate salt supplementation is critical for optimum fertility. An increase in cervico-vaginal mucus sodium during estrus is required for conception. Harris et al., (1986) reported that cows with less than 50 micromoles of sodium per milliOsmol in the urine had a higher return to estrus after 24 days following insemination. These data were interpreted to show that the low sodium intakes increased embryonic mortality. In a later study, supplementing lactating cows with 50 grams of salt daily for 30 days after calving increased mean urine sodium concentration from 23 to 74 micromoles per milliOsmol and calving rate from 24.2 to 60.6%.

In a another study, researchers compared salivary sodium concentrations and conception rates of 1,000 cows on 46 farms in Northern Germany. When saliva sodium concentrations were 87 millimolar or less, conception rates averaged 51%. When the sodium was between 131-147 millimolar, conception rates were 70% or greater. These trials provide conclusive evidence that sodium deficiency does lower conception rates. For beef and dairy producers, high conception rates are a must to remain economically competitive.

Grazing High Potassium Forages

Increased application of nitrogen and potassium fertilizers has raised forage production on many intensively managed pastures. However, as potassium concentrations in forage increase, to often over 2% of the dry matter, sodium levels decrease. In some highly fertilized forages, the potassium:sodium ratio can approach 50:1. Recent British research shows that decreasing this ratio by increasing forage sodium can improve animal performance.

Chiy and Phillips (1991) grazed 24 lactating dairy cows on paddocks where all, one-half, or none of the perennial ryegrass pasture was fertilized with salt at the rate of 50 pounds per acre. Half of the cows received 50 grams of salt per day in their concentrate feed. Salt fertilization increased forage growth rate, sodium concentration (0.29% to 0.49%) and decreased potassium (1.75% to 0.25%). Milk yield and live weight gains were increased by salt fertilization, but not by direct salt supplementation in the concentrate. Grazing time on forage was increased by salt fertilization, but only in cows not receiving supplemental salt. Cows selectively grazed the salt fertilized pastures when given an option. Ruminating time was increased both by salt fertilization and supplementation.

In subsequent experiments (Chiy et al., 1993), voluntary intake of perennial ryegrass fertilized with sodium chloride increased 12% to 18% for both sheep and cattle with sodium levels in forage up to 0.6%. The improved intake may partially result from the increased rumen pH, fluid dilution rate, and digestibility associated with the sodium fertilization.

Lowering forage potassium and increasing forage sodium may also reduce the occurrence of grass tetany, one of the problems associated with some intensively managed pastures. Researchers have known for several years that high potassium intakes decrease magnesium absorption and reduce plasma magnesium. However, recent data reported by Chiy and Phillips (1995) showed that magnesium absorption increased 23% when sodium was added to a high potassium diet. The incidence of grass tetany was halved when sodium chloride fertilizer was applied to pastures grazed by beef cows. Martens et al., (1987) showed that increasing the sodium:potassium ratio alters the electro-physiological conditions of the rumen epithelium to increase magnesium absorption.

In summary, livestock and poultry require adequate levels of sodium supplementation to achieve optimal performance. I have pointed out several conditions which increase the need for supplemental sodium. Dietary sodium intakes are often overestimated. In a recent survey comparing feed analyses from private laboratories with National Research Council data for the same feedstuff, sodium levels were often 10% to 30% of NRC values (Berger 1991). Part of the reason for this discrepancy is that some of the early determinations of sodium concentration were actually estimates. Frequently, chloride was measured and a 1:1 relationship with sodium was assumed. Like any other nutrient, knowing the true sodium requirement in your production environment and meeting those needs through proper supplementation is one of the keys to remaining competitive.

Literature Cited

Arya S.P., and Jain, Y.C. 1986. Sodium and potassium concentrations of cervico-vaginal mucus in relation to oestrous cycle and early pregnancy in Jersey cows. Indian Journal of Animal Science. 56:333.

Berger, L.L. 1991. NRC feedstuff mineral composition data in need of updating. Feedstuffs Jan. 21, 1991. Vol. 63, No.3.

Britton, W.M. 1990. Dietary sodium and chloride for maximum broiler growth. In Proceedings 1990 Georgia Nutrition Conference. p. 152.

Chiy, P.C. and C.J.C. Phillips. 1991. The effects of sodium chloride application to pasture, or its direct supplementation, on dairy cow production and grazing preference. Grass and Forage Science 46:325.

Chiy, P.C. and C.J.C. Phillips. 1995. Sodium in ruminant nutrition, production, reproduction, and health. p. 107. In: Sodium in Agriculture. Phillips, C.J.C., Ed., Canterbury Press. London.

Chiy, P.C. and C.J.C. Phillips, and M.R. Bello. 1993. Sodium fertilizer application to pasture. 2. Effect on dairy cow production and behavior. Grass and Forage Science. 48:203.

Cromwell, G.L., D.D. Hall, G.E. Combs, O.M. Hale, D.L. Handlin, J.P. Hitchcock, D.A. Knabe, E.T. Kornegay, M.D. Lindeman, C.V. Maxwell, and T.J. Prince. 1989. Effects of dietary salt level during gestation and lactation on reproductive performance of sows: A cooperative study. J. Anim. Sci. 67:374.

Davison, T.M., G.M. Murphy, M.M. Maroske, and G. Arnold. 1980. Milk yield response following sodium chloride supplementation of cows grazing a tropical grass-legume pasture. Australian Journal of Experimental Agriculture and Animal Husbandry. 20:543.

Harris, D.J., J.D. Allen and I.W. Caple. 1986. Effects of low sodium nutrition on fertility of dairy cows. Proceedings of the Nutritional Society of Australia 11:92.

Martens H., O.W. Kuble, G. Gable, and H. Honig. 1987. Effects of low sodium intake on magnesium metabolism of sheep. Journal of Agricultural Science, Cambridge. 108:237.

McDowell, L.R., J.H. Conrad, G.L. Ellis, and J.K. Loosli. 1983. In: Minerals for grazing ruminants in tropical regions: Department of Animal Science, University of Florida, Gainesville.

Morris, J.G. and G.M. Murphy. 1972. The sodium requirements of beef calves for growth. Journal of Agricultural Science, Cambridge. 78:105.

Murphy, G.M. and J.A. Connell. 1970. A simple method of collecting saliva to determine the sodium status of cattle and sheep. Australian Veterinary Journal. 46:595.

National Research Council. 1984. Nutrient requirements for poultry. National Academy of Sciences, Washington, DC.

Pimentel, J.L. and M.E. Cook. 1987. Suppressed humoral immunity in chicks fed diets deficient in sodium, chloride, or both sodium and chloride. Poultry Science 66:2005.

Whitlock, R.H., M.J. Kessler, and J.B. Tasker. 1975. Salt (sodium) deficiency in dairy cattle: Polyuria and polydipsia as prominent features. Cornell Veterinarian 65:512.

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