Salt for Dairy Cattle

The sodium and chloride nutrition of lactating dairy cows is critical to optimum production because of the obligatory loss of these nutrients in milk. In addition, dairy cattle are commonly fed high forage diets that are low in sodium and high in potassium. Consequently, a sodium chloride deficiency can develop rapidly in a high producing cow.

The following are the symptoms of salt deficiency reported in Cornell studies (28). The first symptom was a craving for salt that was noticed within two weeks and by four weeks was a consistent observation. After two months, the cows showed a depraved appetite. It was manifested by licking the hands and clothing of barn personnel, consuming quantities of soil soaked with urine or the run-off from the manure pile, licking the barn walls and drinking the urine from other cows during urination. This was followed by a loss of appetite and body weight. In some cows feed intake was reduced to near zero. Milk production decreased as appetite decreased. The cows then assumed an emaciated appearance, developed a dry, rough skin (particularly on the neck), the hair coat became unkempt and the cattle became listless. In terminal cases, there was shivering, a staggered gait (most noticeable in the hind legs), weakness, abnormal heart activity, low body temperature (as low as 96.3°F) and then death. In two cases, where cattle had arrived at this terminal condition, they were given 200 grams of salt and made complete recoveries.

In this study, cattle placed on the salt-deficient diet had averaged approximately 14,000 pounds of milk the previous year (Table 5). During the first year on the salt deficient diet, production dropped to 7,150 pounds, even though the water supplied 10-15 grams of salt daily. During the second year production dropped to approximately half of the first year’s production when a low-salt water source was used. It is likely that the impact on milk production would have been even greater during the first year if the low-salt water would have been used. These data illustrate the importance of sodium chloride nutrition to optimum milk production.

Treatment Daily per Cow, g Salt	Previous Production lb	Production Experiment for 301 Days, lb
0	14,000	7,500
15	16,000	11,265
60	14,600	11,550
120	14,700	11,360

Recently Cornell researchers (198) have fed dairy cows diets containing 0.10%, 0.27% or 0.45% chloride to look at the effects of a chloride deficiency, independent of sodium. Dry matter intake was significantly reduced after 4 weeks, body weights dropped from an average of 575 kg initially to 476 kg by the eighth week of the trial and milk production decreased from 27.7 to 19.2 kg/day for cows fed 0.10% chloride. Other chloride deficiency signs included lethargy, hypophagia, emaciation, hypogalactia, constipation, cardiovascular depression and mild dehydration. The cows frequently licked urine of other cows, chewed on wooden stall dividers and licked metal pipes. These data show that chloride nutrition can be of critical importance in diets of lactating cows. The actual requirement is probably between 0.18% and 0.27% chloride (199).

The 1989 National Research Council publication "Nutrient Requirements of Dairy Cattle" states that "A reasonable estimate of the dietary requirement for milk cows is 0.18% sodium, which is equivalent to 0.46% sodium chloride in the total diet dry matter" (156). This level of salt would provide 0.30% chloride which should be adequate. The 2001 Dairy NRC (286) reported that empirical modeling of data from 15 experiments with lactating cows (1,444 cow-period observations) conducted in either cool or warm seasons showed that dry matter intake and milk yield were improved by dietary concentrations of sodium well above those needed to meet sodium requirements (287, 288). Dry matter intake and milk yield responses over a range of dietary sodium concentrations (0.11 to 1.20 percent, dry basis) were curvilinear, with maximum performance at 0.70 to 0.80 percent sodium, dry basis.

Many dairyman feed total mixed rations, but some still feed the roughage and concentrate separate. In those cases, most dairy scientists recommend that 0.5% to 1.0% salt be added to the concentration mixture fed to dairy cattle (70, 71).

Heat stress increases the sodium requirement above that prescribed by the NRC for cows in a thermal-neutral environment (131). Not only does the sodium requirement, as a percent of the diet, increase due to sweating and decreased feed intake, but prolonged heat stress also reduces blood aldosterone concentrations resulting in increased loss of sodium in the urine (200). In non-lactating Holstein cows, aldosterone concentrations have decreased over 40% during heat stress.

In a 1986 review article, a University of Florida dairy scientist recommends that the total dietary sodium be about 0.5% of the ration dry matter (149). He states that a level of 1% salt supplementation will provide about 0.4% sodium, which, when added to the sodium level naturally found in feed ingredients of the ration, will typically yield about 0.5% sodium in the total ration dry matter. He further states that if dietary sodium is increased from 0.18% to 0.5% in the ration of a lactating dairy cow consuming 42 pounds of dry matter, this will amount to an additional 0.34 pounds of salt per cow per day. This extra salt will cost about 2 cents daily. Based on previous experiments, if two additional pounds of milk are produced daily, this will yield 20-30 cents, which is a sizable return on investment (149).

Israeli researchers (220) have also shown the importance of adequate chloride intake for early lactation cows. Their research showed that during heat stress milk yield was positively and significantly related to chloride and potassium status. These ions are high in sweat and large negatively balances may occur during early lactation. Their data were interpreted to suggest that an increased supply of chloride and potassium above NRC requirements during early lactation may result in increased dry matter intakes and milk yields.

The degree of heat stress will vary with animal and the production potential of each cow. Cows with the highest production potential will usually consume the most feed and thus have the greatest heat load. This is a good reason to feed free-choice salt above that in the basal diet. This allows individual animals to adjust their intake.

Salt Fertilization can Improve Milk Production

Intensive rotational grazing is a dairy management practice that is becoming increasing popular. Maximizing high-quality forage intake is essential to optimizing milk production with this approach. Recent British research (221, 222, 223, 224, 225, and 226) has shown the potential benefits of using salt as a fertilizer when the soil and forage grown on the soils is low in sodium. These researchers have repeatedly reported increases in milk production in cows grazing perennial ryegrass pastures when forage sodium levels were increased from 0.02% to 0.05% by salt fertilization. When given a choice, cows grazed the salt fertilized pasture compared to the unfertilized pastures, spent more time grazing, and had a greater bite rate. Milk yield and weight gain were increased by salt fertilization beyond that achieved by direct supplementation. Water intake and rumen pH were also increased due to salt fertilization which may have allowed the greater dry matter intakes. These data are interpreted to show that salt fertilization of low-sodium forages may increase the potential of using rotational grazing as a management strategy for dairy production.