Restricted Dietary Chloride with Sodium Bicarbonate Supplementation for Holstein Cows in Early Lactation

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Abstract
Over 2 wk, beginning 3 wk postpartum, daily changes of feed and water intake and milk production and composition were monitored in 25 cows allotted randomly among 4 dietary treatment groups differing in sodium chloride, sodium bicarbonate and ad lib supplementation by salt block. The basic complete diet was 54% corn silage, 27% shelled corn and 16% soybean meal, dry basis. The 4 dietary treatments were control, 0.42% chloride; low, 0.10% chloride; low plus salt block, complete ration same as low with ad lib salt block consumption; and control plus 0.7% sodium bicarbonate. Differences were consistently significant only for electrolyte concentrations in blood serum, urine and feces of cows fed the low diet. In blood serum, chloride declined from 96.4 .+-. 3.5 to 83.4 .+-. 4.5 meq/l and serum total CO2 rose from 28.4 .+-. 1.9 to 36.9 .+-. 2.6 meq/l. Anion gap increased from 19.0 .+-. 2.9 to a high of 23.4 .+-. 3.5 meq/l in blood serum at day 11. Metabolic derangements of cows fed the low diet may be summarized as subclinical primary hypochloremic, secondary hypokalemic metabolic alkalosis.