AbstractsBiology & Animal Science

Chromic oxide (Cr2O3) was found to be satisfactory for determining the digestibility of rat and pig rations. For sheep, the index was useful only if the ration contained 35%, by weight, of a ground non-roughage material. Limitations were pointed out in the regression method of determining indirectly the digestibility and metabolizable energy of sheep and pig feeds. Associative digestibility complicated these determinations. It was also emphasized that relatively large amounts of supplement must be added to a basal ration to obtain reliable digestion coefficients for the former. In calculating the physiological fuel values of a feed for sheep, need was indicated for a specifie determination of the urinary and gaseous energy lasses. Following a change in sheep or pig ration composition, a length of time, considerably longer than the usual preliminary feeding periods used for these species, was required before digestibility became constant and maximum.