The effect of age and weaning on enzyme activities of abomasum and pancreas of the lamb was studied. Sixty-nine lambs were either maintained at the preruminant stage until 42 days of age or weaned between 20 and 30 days. They were slaughtered between birth and 100 days, and the mucosa of their abomasum and their pancreas were collected. At 2 days of age there was a threshold of glandular growth and of development of enzyme secretory potentialities. Pancreas showed an extensive hyperplasia without growth until day 2; its weight increased after day 7 but only by hypertrophy. Quantities of gastric enzymes in relation to empty live weight increased between birth and 2 days, but that of chymosin then decreased, whereas pepsin did not change significantly; effects of weaning were similar. The evolution of pancreatic enzyme activity was usually the reverse of that of chymosin; however, trypsin activity was low at birth and that of colipase did not increase at weaning. The ratio of colipase to lipase was always higher than 1, showing that lipase always was saturated in the lamb. The pancreas seemed to take over the secretion of abomasal proteolytic enzymes. Potentialities of enzyme digestion appeared to be influenced mainly by the age or weight of the animal; these potentialities were minimal for at least several days during the first neonatal week and, if there was enzymatic adaptation to the amounts of the ingested substrate, it did not occur rapidly.
Using fistulated calves, the influence of the age, type of dietary protein and weaning on the secretion of chymosin and pepsin by the abomasum were studied. The abomasum secreted both chymosin and pepsin when the animals were fed milk. Chymosin secretion appeared to be independent of the age of the animals, whereas a slow increase in pepsin secretion was observed as the calves aged. Several preruminant animals were fed either a skim-milk diet or a milt substitute in which proteins were provided by fish, soya or whey concentrates. Each of these 3 milk substitutes led to a decrease in chymosin secretion without modification of pepsin secretion. Chymosin secretion was partly restored when the calves were again given a skim-milk diet. At weaning, chymosin secretion dropped abruptly, but the pepsin level was not affected. These results indicate that milk (most probably its casein fraction) is responsible for the activation of chymosin secretion.For the newborn mammal, milk is the main food, and growth depends on its efficient absorption from the digestive tract. Coagulation of the caseins in the stomach controls and slows down the flow of the chyme into the duodenum at a time when the volume of pancreatic secretion is still low. Pepsin, chymosin (if present) and hydrogen ions are responsible for milk coagulation.In the preruminant animal the functional part of the stomach is the abomasum which secretes chymosin, a milk-clotting acid protease. It was once considered that the level of pepsin was very low in the abomasum of the milk-fed calf and that at weaning the consumption of solid food caused chymosin secretion to cease and pepsin secretion to increase (Berridge et al. 1943). However, Grosskopf (1959), Henschel, Hill & Porter (1961) and Hill, Noakes & Lowe (1970 have shown that, even in milk-fed calves, appreciable pepsin activity could be detected in the abomasum. Garnot et al. (1974) have presented quantitative data on the chymosin and pepsin levels in the abomasum of slaughtered preruminant calves. So far, there is little information on the effect of age on these levels. Nain et al. (1972) observed a decrease in chymosin secretion at 3 months of age, but the diets were not specified. The clotting activity was found to be high in the abomasum of the fetal cab 0 (Kirton, Paterson &
SummaryCamembert cheeses were made with pasteurized skim milk or with ultrafiltered milk concentrated 2-fold, using either rennet or Mucor miehei proteinase as coagulant. Using rennet, the rapid acidification during cheesemaking increased enzyme retention and 55% was retained after 24 h. With the M. miehei proteinase, acidification had no effect and only 17% of it was retained after 24 h. The use of ultrafiltered milk resulted in less rennet being retained in the curd.
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