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Proteolytic Activity and in Vitro Enzyme Stability in Small Intestinal Contents from Ruminants and Nonruminants at Different Ages^1,2,

Research Station, Canada Department of Agriculture, Fredericton, New Brunswick, Canada, and Department of Dairy, Michigan State University, East Lansing, Michigan

Trypsin and chymotrypsin esterase activities and protein nitrogen were determined in digesta from the small intestine of calves and lambs fed liquid milk diets, from calves and sheep fed hay, and from rats and chickens fed concentrate diets. Total enzyme activities and in vitro protein digestion (digesta incubated for 2 hours at 37°) per unit body weight increased with both age and rumen development in calves. Total enzyme activities in lamb digesta were greater at 6 weeks than at 2 weeks of age, but were somewhat lower from yearling ruminating sheep, and in vitro protein digestion per unit body weight tended to decrease with age. Trypsin activity remained fairly constant in rat digesta from 1 to 9 months of age, but chymotrypsin activity declined. Lamb digesta had more enzyme activities per unit body weight than digesta from calves up to 41 days of age but less protein was digested in vitro. Except for 2-week-old lambs, digesta from the lower section of the intestine from all species had about 50% less protein, and less in vitro protein digestion than in digesta from the upper one or two sections. This indicated small amounts of readily digestible protein were present in the lower intestine. Less chymotrypsin than trypsin activity was retained during incubation of the digesta. Ratios of chymotrypsin-to-trypsin activities ranged from 0.6 to 0.8 in the bovine and ovine digesta, and 0.96 to 2.46 in the rat digesta.

² Taken in part from a thesis submitted by the senior author to the Graduate School of Michigan State University, in partial fulfillment of the requirements for the Ph.D. degree.

Manuscript received 25 May 1968.