Mineral requirements of dairy cows, comparison of different systems

Abstract

There is good international agreement for dietary allowances of Mg, Na, K, S and trace elements. Nevertheless, some discrepancies still exist for maintenance requirement of P and true absorption of Ca. The low level of P for maintenance in the NRC system (1988) is reliable for low forage level diets in which the recycling of P via saliva is also low. True absorption of Ca ranges between 35 and 38 % in almost all systems, except the Australian one (60 %). This data results probably from a good adaptation to very low calcium levels in the diet, but this is not representative of practical conditions of animal feeding. Data for growth, pregnancy and lactation are very close in the different systems. French recommendations (INRA 1978 and 1988) are in fact practical dietary allowances with a safety margin included, their objective is to satisfy mineral requirements of all animals. These data also take into account the bone mineral mobilisation at the beginning of the lactation. These recommendations are normally higher than minimum mineral requirements.