Relationship Between Ionized and Total Calcium, Albumin, and the Prevalence of Subclinical Hypocalcemia in Holsteins Fed Anionic Diets

The relationship between ionized calcium (iCa), total calcium (tCa), albumin (Alb) concentrations and the prevalence of subclinical hypocalcemia (pSCH) around calving remains unclear, especially in dairy cows fed anionic diets (AD) or not fed AD (non-AD). The present study investigated the concentrations and ratios of iCa, tCa and Alb in association with pSCH in dairy cows fed AD and non-AD diets in close-up. The concentrations of iCa, tCa, and Alb were analyzed within 72 hours after calving in 120 Holsteins from 23 different farms fed AD (n = 78) and non-AD diets (n = 42). The pSCH was analyzed based on iCa < 1.00 and 1.05 mmol/L and tCa < 2.00 and 2.10 mmol/L. The pSCH of 30.8% and 47.4% in AD and 47.6% and 59.5% in non-AD was for iCa < 1.00 and < 1.05 mmol/L, respectively. The pSCH was 46.2% and 56.4% in AD and 45.2% and 61.9% in non-AD, based on tCa < 2.00 and 2.10 mmol/L, respectively. The iCa/tCa ratio was significantly higher in AD-fed cows (58.0 ± 23.7%) compared to non-AD cows (48.7 ± 12.8%; P < .01). The Alb concentration was significantly lower in AD compared to non-AD. The iCa value was significantly higher in AD compared to non-AD. The tCa value between AD and non-AD was not significantly different. AD increased the iCa concentration, the iCa/tCa and tCa/Alb ratio. The pSCH value was lower in AD than in non-AD according to iCa values. The iCa value allowed a better differentiation of pSCH between AD and non-AD groups than the tCa value.