FACTORS AFFECTING THE APPLICATION OF ON–LINE MILK UREA SENSING

Abstract

Estimation of urea in the milk of dairy cows is routinely done to determine how efficiently the animals are using dietary nitrogen. The observed values are used to adjust the herd ration to minimize feeds costs, improve the health of the herd, and reduce nitrogenous waste from the farm. Real–time data supplied by a recently developed on–line urea sensor may improve the quality of nutritional management by allowing more frequent sampling and automated analysis of milk. For effective application and interpretation of data from the device, we undertook an analysis of several factors affecting the dynamics of milk urea in dairy cows. Analysis of variations among cows indicated that interpretation of milk urea should be based on averages of 10 or more cows in a group. Based on observed changes in milk urea during milking, milk sampled as soon as possible after ejection of the foremilk would be representative of the entire milking. Consistent diurnal patterns in milk urea were observed, stressing the importance of uniform sampling time when evaluating milk urea. The nitrogen content of the ration was shown to have a strong positive effect on milk urea and no significant effect on yield, demonstrating the importance of balancing the diet. Evidence of heat stress was observed, with a positive effect on milk urea and a negative effect on yield. High nitrogen in the diet and periods of possible heat stress were both associated with an increase in the variation of milk urea in a group of cows, indicating that monitoring variance as well as mean milk urea may improve the ability to identify abnormal conditions at the dairy. Finally, changes in milk urea were observed within 3 days of changes in experimental conditions, suggesting that the ability to track milk urea every day may lead to faster and less ambiguous diagnosis of nutritional problems.