Effect of Heating Milk on the Time which the Curds Remain in the Abomasum of Calves

Abstract

Using a modification of the Hill technique it was found that boiling of skim milk for 3 minutes in an open container on an oil bath lowered the curd tension about 80 per cent. Pasteurizing skim milk at 142° F. for 30 minutes in a vat pasteurizer reduced the curd tension about 20 per cent. Autoclaving at 242° F. for 15 minutes reduced the curd tension to zero. Plain condensed skim milk when diluted to the specific gravity of average skim milk gave a curd tension near that of boiled milk. The rate at which these milks leave the stomach was then studied by palpating the curd mass in the abomasum through the wall of the rumen. Two liters of raw skim milk usually left the abomasum in about 12 to 18 hours when fed by stomach tube. The evacuation time of the same quantity of boiled milk was usually 8 to 12 hours. Equivalent amounts of boiled and autoclaved milk remained in the stomach about the same length of time. At varying intervals of time, curd was removed through a gastric fistula from the stomach of calves. The data indicate that equal amounts of raw and boiled milk are liquefied at much the same rate during the first 3 to 6 hours. After this the boiled milk liquefies at a faster rate. Measurements of the total acid, free acid and hydrogen-ion concentration were made upon the gastric contents of calves which had been fed test meals of equivalent quantities of raw and heat treated milk. Boiled milk and autoclaved milk leave the stomach more quickly than raw milk. This is not because the gastric juice varies in acidity when these milks were fed, but more likely because the effect of heat lowers the curd tension and thus permits the curd to break up more easily. The breaking up of the curd furnishes a greater surface for the gastric juice to attack. Raw milk coagulates in the stomach of the calf in from 1 to 10 minutes. Boiled and autoclaved milk coagulate more slowly in the stomach— usually requiring 8 to 15 minutes. The variability of the results obtained with the same type of test meal fed under as nearly identical conditions as possible are probably due to fatigue, individuality and the state of health of the animal. © 1935, American Dairy Science Association. All rights reserved.