Marginal mineral deficiencies and their importance for the productivity and reproductivity of domestic animals

Using selenium as an example some aspects of trace element metabolism especially in swine have been discussed in the preceding paper. Several investigations indicate that the chemical form of an element in the feed may influence its availability to and metabolism by the animals. Results lending further support to this are presented and discussed. A normal physiological condition which greatly enhances the requirement for nutrients including trace elements is pregnancy. The placental transfer of selenium is discussed in some detail and a survey of the theoretical minimum requirements for several elements at various stages of pregnancy is given. The possible relationship between marginal subclinical deficiencies and animal health especially the resistance towards infectious diseases is also touched upon. During the past few decades marginal mineral deficiencies or imbalances have become prominent problems in many parts of the world and under widely varying animal production systems. The possible causes of this unfortunate development are considered and the advantages and disadvantages of various methods to detect such conditions discussed. Special emphasis is laid upon screening methods suitable for depicting geographically limited areas where marginal deficiencies may be suspected to occur. In recent years the existence of genetically controlled variation in the trace element content of blood and tissues i.e. in the biochemical profile of animals belonging to the same race has become evident. These findings make it difficult to speak about ''normal'' values in blood and tissues. They also hamper the possibility of establishing normal requirements for the various trace elements