Effect of a metabolically created systemic acidosis on calcium homeostasis and the diurnal variation in urine pH in the non-lactating pregnant dairy cow

Abstract

Reducing the dietary cation-anion difference (DCAD) has been shown to be an effective means of preventing parturient paresis in confinement systems where cows are offered a total mixed ration containing DCAD-reducing mineral compounds (anionic salts). Such a supplementation strategy is not possible in cows being group fed forages precalving, and little is known about the effect of supplementing these cows with large amounts of anionic salts twice daily.Eight non-lactating, pregnant Holstein-Friesian cows were allocated to two levels of DCAD ( -20 and +18 meq/100 g DM) for 24 d, with an intensive Ca balance undertaken in metabolism stalls following a 2-week acclimatization to diet. The basal diet was 3 kg DM of crushed barley and 7 kg DM of pasture-hay. Urine and faeces were collected separately, weighed daily for 5 d and analysed for Ca content. Urinary Ca, creatinine and hydroxyproline concentration and plasma Ca concentration were determined during the period of the balance study. The diurnal pattern in urine and rumen pH was determined over 2 d. Decreasing DCAD reduced (P <0 . 001) the pH of urine, and increased (P <0 . 05) Ca absorption. Plasma Ca concentration was not affected by DCAD, and DCAD did not affect the output of urinary hydroxyproline, a marker of bone resorption. Twice-daily supplementation of anionic salts was sufficient to reduce the pH of blood and increase gastrointestinal Ca absorption. There was no diurnal variation in the pH of urine, suggesting that time of sampling to determine efficacy of DCAD in reducing systemic pH was not important.

Effect of decreasing dietary cation anion difference on feedlot performance, carcass characteristics, and beef tenderness1,2

“…Horst et al (1997) proposed that urine pH of 5.5 to 6.2 was indicative of compensated metabolic acidosis. Ingestion of a low DCAD diet increases Ca entry into the exchangeable Ca pool by 3 main mechanisms: enhanced intestinal absorption (Lomba et al, 1978;Schonewille et al, 1994;Roche et al, 2007), increased bone resorption (Block, 1984), and decreased bone accretion (van Mosel et al, 1994), with the latter 2 mechanisms appearing to be active only in the presence of acidemia and metabolic acidosis. However, ingestion of a low DCAD diet also increases Ca exit from the exchangeable Ca pool by decreasing renal tubular Ca reabsorption (Stacy and Wilson, 1970;Fredeen et al, 1988).…”

Periparturient effects of feeding a low dietary cation-anion difference diet on acid-base, calcium, and phosphorus homeostasis and on intravenous glucose tolerance test in high-producing dairy cows

“…The increase in Ca flux is due to an increase in the rate of Ca entry into the exchangeable Ca pool that approximates the rate of Ca exit from the exchangeable Ca pool (Vagg and Payne, 1970;Fredeen et al, 1988). Ingestion of a low DCAD diet increases Ca entry into the exchangeable Ca pool by 3 main mechanisms: enhanced intestinal absorption (Lomba et al, 1978;Schonewille et al, 1994;Roche et al, 2007), increased bone resorption (Block, 1984), and decreased bone accretion (van Mosel et al, 1994), with the latter 2 mechanisms appearing to be active only in the presence of acidemia and metabolic acidosis. Ingestion of a low DCAD diet also increases Ca exit from the exchangeable Ca pool by decreasing renal tubular Ca reabsorption (Stacy and Wilson, 1970;Fredeen et al, 1988), manifest as hypercalciuria.…”

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

“…As already described, urinary Ca can be increased or minimised during the time lag for intestinal and bone adaptation, but reabsorption is as high as 99 % (1) . Therefore, urinary losses are as low as 0·4 g/d (48) and 0·8 g/d (87) . An exception to this rule is when dietaryinduced metabolic acidosis causes hypercalciuria.…”

“…An exception to this rule is when dietaryinduced metabolic acidosis causes hypercalciuria. The urinary Ca excretion increases in a curvilinear fashion as the systemic pH decreases and can be as high as 6 (48) , 5·3 (87) or 7·9 g/d (124) .…”