EFFECT OF THE COW'S BODY CONDITION AND STAGE OF LACTATION ON DEVELOPMENT OF MILK RANCIDITY1

Abstract

An objective of this study was to investigate the relationship between body condition of the dairy cow and susceptibility of milk to rancidity. Initial milk samples were obtained from 166 cows in Spring, 1969, and all animals were retested after an interval of two months. Additional observations included the effects of stage of lactation, level of milk production, and herd effects. Each cow was evaluated for body condition, at the times when milk samples were obtained, by a method based on measures of weight and skeletal size and by a subjective scoring system. Spontaneous rancidity of the milk fat was allowed to develop upon storage for 48 hr; and induced rancidity was brought about by controlled agitation. As measured by acid degree values (ADV) the treatments imposed on the milk samples were successful in simulating development of spontaneous and induced lipolysis of the milk fat. However, the magnitude of the ADV was not related to body condition score. It is concluded that in well-fed herds, such as those used in this experiment, body condition of the cow does not influence the susceptibility of her milk to rancidity. These data may not apply under conditions of poor feeding and management. Advancing stage of lactation was associated with increases in both spontaneous and induced rancidity. This was indicated by positive correlations between days in milk and ADV, and by significantly higher values in the second sampling period than in the first. There was a negative correlation between the amount of milk produced and ADV. This may have been related to the decline in milk flow which accompanied advancing lactation. An unexplained herd difference existed with respect to the susceptibility of milk to induced rancidity.