Addition of Chloride to a Prepartal Diet High in Cations Increases 1,25-Dihydroxyvitamin D Response to Hypocalcemia Preventing Milk Fever

Abstract

In this study, we present evidence that cows fed highly cationic diets are less responsive to parathyroid hormone than those fed a highly anionic diet. Forty-seven Jersey cows (55 mo of age) were fed an alfalfa haylage-based diet supplemented with either anions (Cl-) or cations (Na+). Cows fed the high cationic diet suffered significantly more cases of milk fever (6 out of 23) than those fed the high anionic diet (1 out of 24). Concentrations of Ca at parturition and the first 2 d of lactation were significantly higher in cows fed the anionic diet. Secretion of parathyroid hormone in response to developing hypocalcemia was similar in cows fed either diet. Plasma hydroxyproline concentration (an index of bone Ca resorption activity) was greater in cows fed the anionic diet, suggesting better utilization of bone Ca. Plasma 1,25-dihydroxyvitamin D concentration was correlated inversely with plasma Ca and related directly to plasma parathyroid hormone in both groups of cows. However, the magnitude of the response (the amount of 1,25-dihydroxyvitamin D produced per unit increase in parathyroid hormone) was reduced greatly in cows fed the high cation diet. Because parathyroid hormone regulates both bone Ca resorption and renal 1,25-dihydroxyvitamin D production, these data suggest that prepartal diets high in cations decrease the ability of bone and renal tissues to respond to parathyroid hormone. Addition of anions to prepartal diets can reduce the excess cation balance of diets, increasing tissue response to parathyroid hormone and enabling the cow to better adapt to the Ca demands of lactation.

Fractional excretion of electrolytes during pre- and postpartum periods in cows

“…However, the effects of Ca and PO 4 contents in the anionic diet on mineral metabolism are not fully understood. An anionic diet is thought to induce metabolic acidosis which increases Ca resorption from the bones and urinary Ca excretion (Gaynor et al, 1989;Goff et al, 1991;Wang and Beede, 1996). In this study, although there were changes in plasma Ca and PO 4 values in cows fed a diet containing low Ca-low PO 4 in the peripartal phase, statistically significant difference could not be seen.…”

“…Feeding low Ca-low PO 4 or anionic diets during the dry period tends to reduce hypocalcaemia, while high Ca-high PO 4 or cationic diets tend to induce it (Kichura et al, 1982;Gaynor et al, 1989;Goff et al, 1991). However, the effects of Ca and PO 4 contents in the anionic diet on mineral metabolism are not fully understood.…”

A novel model to explain dietary factors affecting hypocalcaemia in dairy cattle

“…It has been proposed that metabolic alkalosis reduces renal responsiveness to PTH (51) and that this may be reversed by metabolic acidification. Furthermore, improved responsiveness to calcitriol at a lower DCAD has been suggested (92) . However, a positive DCAD is not unique to the periparturient period.…”

“…A high DCAD has been explained as a negative factor for Ca metabolism (89,92,93) rather than a negative DCAD as a positive factor against milk fever. It has been proposed that metabolic alkalosis reduces renal responsiveness to PTH (51) and that this may be reversed by metabolic acidification.…”

Anionic salts and dietary 25-hydroxyvitamin D stimulate calcium availability in steers

“…This can lead to a delay in both the release of Ca from skeletal storage and active absorption in the small intestine when a sudden Ca demand is initiated . Anionic diets have been shown to increase both Ca absorption and skeletal mobilisation before parturition and therefore have been effective at reducing the incidence of hypocalcaemia (Fredeen et al, 1988;Goff et al, 1991;DeGroot et al, 2010).…”