Effects of anionic salts in a pre-partum dairy ration on calcium metabolism

The effects of anionic salts in the transition diet on serum and urine calc ium at calving and on peripartal health, subsequent milk production and fer tility performance were studied in a well-managed, high-producing Friesland dairy herd. Over a period of a year, approximately 21 days before the expe cted date of calving, 28 pre-partum heifers and 44 multiparous dry cows wer e randomly allocated within parity to 1 of 2 transition diets, designated c ontrol and experimental anionic diets. The anionic diet contained the same quantities of the basic transition ration fed to the control group as well as a standard anionic salt mixture containing 118 g NH4Cl, 36 g (NH4)(2)SO4 and 68 g MgSO4 (total 222 g) per animal per day. This reduced the DCAD to -11.68 mEq/100 g dietary dry matter compared to +13.57 for the control diet . Blood and urine were randomly sampled from 7 to 8 animals within each cat egory within 3 hours post-partum. Serum calcium (total and ionised) and cre atinine, urine calcium and creatinine and the fractional clearance of calci um were assessed. Relevant clinical, milk production, and fertility data we re collected. The total serum calcium (2.07 versus 1.60 mmol/l), serum ioni sed calcium (1.12 vs 1.02 mmol/l), urine calcium (0.92 vs 0.10 mmol/l) and the fractional clearance of calcium (1.88 vs 0.09 %) were significantly hig her (P < 0.01) at calving for multiparous cows fed the anionic diet compare d to those fed the control diet. In the primiparous cows there were no sign ificant differences in serum calcium levels. However, the urine calcium (1. 07 vs 0.43 mmol/l) and the fractional clearance of calcium was higher (1.75 vs 0.45 %) in cows fed the anionic diet (P <0.05 and 0.01 respectively). T hese results illustrated that there were benefits, although no differences were demonstrated with respect to health, milk production or fertility. The supplementation of diets with anionic salts in the last 2-3 weeks before c alving has the potential to significantly improve parturient calcium homeos tasis.