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Changes in Milk Products Sham Fed to Calves. II. Relation of Prefeeding Heat Treatments and Open-Pail and Nipple Systems of Feeding on Lipolysis in Whole and Separated Milks¹

Department of Dairy Science, South Carolina Agricultural Experiment Station, Clemson

ABSTRACT

Sources and intensity of lipolytic activity in sham-fed whole and separated milks were explored by determining the relative changes effected by prefeeding pasteurization and by the system of feeding the milks. Nonfed milks, controls, were compared with those sham fed from either an open-pail or a nipple feeder to two rumen-fistulated calves. Portions of controls and sham-fed milks were incubated 12 hours at 38 C. Samples were collected before incubation and at two-hour intervals during incubation for measuring lipolytic activity and accompanying changes in pH and bacterial counts.

Sham feeding effected immediate increases in lipolysis and in bacterial counts of both whole and separated milks and decreases in pH in whole milk. These changes involving lipolysis were accentuated by nipple feeding but were modified only slightly and inconsistently by prefeeding pasteurizations. Initiation of lipolysis through sham feeding and amplification by nipple consumption indicate that the activity of the lipolytic enzymes is related closely to the exposure of the milks in the oral and esophageal areas of the calf. Preponderance of volatile fatty acids in the sham-fed complex of milk and secretory fluids suggests that the enzymes involved preferentially released short-chain fatty acids.

During incubation, particularly after four hours, bacterial counts and free fatty acids (FFA) increased in the sham-fed milks, but lipolytic activity therein showed no marked changes. Thus, the increased FFA probably were due to microbial metabolism. Neither the lipolytic agents normally present in the milks nor those added by bacterial action in sham feeding affected lipolysis to a marked degree, but the acids present in milk contributed a small and highly variable percentage of total acidity in the sham-fed complexes.

¹ Technical contribution no. 678, South Carolina Agricultural Experiment Station, Clemson University, Clemson, South Carolina. Published by permission of the Director.

² Department of Animal Science, North Carolina State University at Raleigh.

³ Rogers Brothers Company, Idaho Falls, Idaho.

⁴ Mocksville Feed Mills, Inc., Mocksville, North Carolina.