Assay and use of magnesium ferrite as a reference in absorption trials with cattle.

Magnesium ferrite, an inert ferrimagnetic material, was introduced as reference substances in absorption trials with ruminants. A method for assaying magnesium ferrite was based upon the difference between the weight of the test material on an analytic balance and that of the same material weighed below a permanent magnet. Four heifers in two pairs were in a feeding experiment lasting for 6 wk divided into two 3-wk periods. Each animal received once daily 12 g magnesium ferrite and, as control, 12 g shredded paper impregnated with 4.2 g chromium oxide. The rations were composed of chopped wheat straw and concentrates, given twice daily, with a different straw-concentrate ratio for each group. The treatments were reversed after the first experimental period. Mean recoveries of magnesium ferrite and chromic oxide in total collection of feces were 103 and 90.2%. Mean absorption coefficients of organic matter calculated by total collection and by the ratios of magnesium ferrite and chromic oxide in feces taken from the rectum were 68.1, 70.1, and 65.7%. The method is simple and accurate and may replace methods involving time consuming chemical determinations.