Milk clotting activity in bovine fetal abomasa

Abomasa (vells) were removed from 30 fetal calves at each of the 6th, 7th, 8th, and 9th mo of development. Milk clotting enzymes were exhaustively extracted in 10% NaCl solutions from the dried abomasal tissue. Total enzyme activity at each stage of fetal development was compared with that from abomasa of 3 to 5-day-old milk-fed calves. Enzyme activity was present in the abomasa of bovine fetuses as early as the 6th mo of development and increased as the fetuses approached full term. Average activity recovered from fetal vells at the 6th, 7th, 8th, and 9th mo of development represented 2, 7, 12, and 31% of the activity per vell, and 8, 14, 22, and 38% of the activity per unit vell weight, of that recovered from high quality calf vells. Diffusion patterns on casein-agar gels produced by bovine fetal extracts differed from those produced by commercial calf rennet extract or porcine pepsin.