Influence of age, dietary protein and weaning on calf abomasal enzymic secretion

Abstract

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 &

Immunohistochemical studies on the development of prochymosin‐ and pepsinogen‐containing cells in bovine abomasal mucosa.

“…The ratios of the enzymes in the present material are shown in Table 1. DISCUSSION The secretion of chymosin from the gastric mucosa is highly correlated with milk-feeding and age (Garnot et al 1977;Andren et al 1980Andren et al , 1981 Several workers (Corpron, 1966;Rubin, Ross, Sleisenger & Jeffries, 1968;Matsuyama & Suzuki, 1970) have suggested that the mucous neck cell is the precursor of the chief cell, and Kataoka (1970) observed groups ofimmature chiefcells in the upper part of the base in gastric glands of the mouse. If this is so, the following hypothesis might explain the lack ofprochymosin-containing chief cells in the lower base of older animals (see also Fig.…”

“…If it is possible to stimulate prochymosin production in older calves by milk-feeding, the stimulus from milk in this experiment probably was too low to induce more than a few mucous neck cells to differentiate into chief cells producing both proenzymes. One reason for this might have been that the milk was entering the rumen instead of the abomasum, as a consequence of an incomplete closure of the oesophageal groove, thereby not providing enough stimulus for the prochymosin production (Garnot et al 1977;Andren et al 1981).…”

In vivo milk digestion in the calf abomasum. II. Milk and whey proteolysis

“…Gastric proteolysis is due to pepsins and chymosin (Berridge et al, 1943 ;Garnot et al, 1977). It has been shown that these enzymes rapidly cleave the Phe 105-Met 106 bond in x-casein (Delfour, Alais and Jolles, 1966) and that this single splitting is responsible for milk clotting.…”

In vivo milk digestion in the calf abomasum. — I. Whole-casein digestion

“…It has been considered that, although the quantity of pepsin is very low in this stomach compartment of milk-fed calves, it has appreciable activity (Berridge et al, 1943 ;Garnot et al, 1977 ;Guilloteau et al, 19831. ln vitro proteolysis of casein by chymosin or pepsins is relatively well known (Delfour, Alais and Jolles, 1966 ;Fox and Walley, 1971 ;Creamer, Mills and Richards, 1971 ;Hill, Lahav and Givol, 1974 ;P61issier, Mercier and RibadeauDumas, 1974 ;Visser and Slangen, 1977 ;Fox, 1977, 1979a, b ;Addeo, P61issier and Chianese, 1981 ;Visser, 1981 proteolysis of milk-proteins in the stomach. These studies deal with gastric emptying in rats (Zebrowska, 1968 ;Buraczewski et al, 1971 ;P61issier, 1981, 1983), pigs (Braude et al, 1970a, b) and calves (Toullec, Thivend and Mathieu, 1971 ;Ternouth and Roy, 1973 ;Guilloteau et al, 1975Guilloteau et al, , 1979P61issier et al, 1983) fed with milk or casein diets.…”