Clotting Factor in Bovine Preruminant Nutrition

Abstract

During the process of digestion in the preruminant calf, the casein protein in cows' milk clots in the abomasum due to the action of the enzymes pepsin and rennin (chymosin) and hydrochloric acid. The importance of this clotting mechanism has been studied, but the physiological implications are not fully understood. Today in the United States, many calves are raised very successfully on milk replacers that do not contain casein protein because skim milk powder, which is the main source of casein, is prohibitively expensive. Instead, whey proteins are the predominant source of milk proteins in calf milk replacers. Research indicates that whey proteins, which do not clot in the abomasum, are as efficacious as casein proteins in the diet of the preruminant calf.

The subject of "clotting" has become topical due to an attempt through the National Dairy Heifer Evaluation Program (which is a part of the National Animal Health Monitoring System) to evaluate milk replacers on farms by a rennet clotting test. This test was developed in Europe to determine the presence of heat denatured skim milk in calf milk replacers and has no relevance to milk replacers formulated on the basis of whey proteins.

This paper reviews the physiology of digestion in the calf, discusses the implications of milk clotting and addresses the issues of modern milk replacer formulations.