Published online by Cambridge University Press: 09 March 2007
1. Hereford steers, housed in concreted yards and given demineralized water, were offered ad lib. a low-sodium (0.07 g Na and 4.5 g potassium/kg) basal diet of sorghum grain, urea and minerals, to which 0, 15 or 30 g K as KHCO3/kg diet had been added. Mean daily intakes of K were 26, 107 and 168 g/steer respectively.
2. The steers were given daily supplements of 0, 3.25 or 6.50 g Na as NaHCO3/steer, added to the food; mean daily intakes of Na (food plus supplemental NaHCO3 minus residues) were 0.41, 3.06 and 6.26 g/steer respectively.
3. Rate of gain of body-weight was positively related to the rate of Na supplementation and negatively related to the K content of the diet, but there was no interaction between Na and K contents of the diet.
4. The Na: K ratios for the parotid saliva from steers not given Na supplements was 0.3, whereas steers ingesting either 3.1 or 6.3 g Na/d had Na: K ratios of about 12. Increasing the amount of K in the diet had no consistent effect on the saliva Na: K ratio. The Na: K ratios for rumen fluid reflected changes in the saliva Na: K ratio in response to Na supplements and were inversely related to the amount of K in the diet.
5. The width of the adrenal zona glomerulosa from steers receiving the basal diet, without Na supplements, was significantly greater than that from steers given the Na supplements, but it was not affected by the amount of K in the diet.
6. Both Na supplements and the diet containing 30 g added K/kg significantly increased the Na: K ratio of the plasma.
7. The addition of 200 mg DL-α-tocopheryl acetate/steer per d to the diet had no significant effects on the growth rate of the steers.
8. It was concluded that the Na requirement of steers for growth was not significantly affected by the amount of K in the diet up to 168 g/d.
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