Coprophagy and Vitamin B12 in the Rat.

The importance of coprophagy in nutritional studies has long been recognized; already in the early days of vitamins numerous workers demonstrated the presence of B vitamins in the excreta of birds and mammals (cf. Kon, 1945; Elvehjem, 1948; Mickelsen, 1956) and began keeping experimental rats on screens to prevent their consuming their droppings. Rats kept in this way have been used for assays of members of the vitamin B complex and have shown characteristic signs of deficiency in the absence of any one of them. However, additional measures have usually been necessary to cause rats to exhibit deficiency of biotin, folic acid or vitamin B,, . These vitamins are needed in only small amounts by the rat and are synthesized in appreciable quantity by many micro-organisms. It has been generally assumed that sufficient biotin and folic acid were synthesized and absorbed from the caecum to supply the animals’ requirements, for the appropriate deficiency could be induced when synthesis was depressed by the inclusion in the diet of sulphonamide drugs (cf. Mickelsen, 1956). The picture with vitamin B,, was less clear; the absorptive mechanism for this vitamin is more complicated and it seemed unlikely that absorption occurred from the caecum. However, it was considered that the difficulty in inducing deficiency was due to storage of the vitamin in the tissues, and it was found that the onset of deficiency could be hastened on increasing the metabolic rate by inclusion of desiccated thyroid in the diet (Ershoff, 1947). It now seems probable that coprophagy was the main reason for these difficulties in inducing certain vitamin deficiencies, and it is noteworthy that du Vigneaud, Chandler, Moyer & Keppel(1939) pointed out already 25 years ago that rats can practise coprophagy even when kept on screens. The full extent of this practice was not really appreciated until Barnes, Fiala, McGehee & Brown (1957) designed an effective cup for collecting faeces (described in the rest of this paper simply as ‘cup’) which they used to show that rats kept on screens normally ingest about half their daily output of faeces. Later, using the same technique, they were able to induce deficiencies of biotin (Barnes, Kwong & Fiala, 1959), folic acid (Barnes, Fiala & Kwong, 1963) and vitamin B,, (Barnes & Fiala, 1958) in rats given appropriate deficient diets and without recourse to other expedients. Subsequently, Morgan (1960a, b) showed that the condition of refection