Effect of Infection Status on Quarter Milk Production and Composition Following Omitted Milking

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Abstract
Sixteen cows in middle to late lactation were milked for 3.5 days at 12-h intervals except for a 24-h interval between 3rd and 4th milkings. A cowside quarter milking unit was used. Quarters were classified by infection status. Milk Cl, lactose, somatic cell concentrations, N-acetyl-.beta.-D-glucosaminidase activity and cell differential counts were determined. Following the omitted milking, concentrations of milk Cl and somatic cells were elevated and lactose concentration reduced in infected quarters. In uninfected quarters, Cl concentration increased, and lactose concentration decreased after the 24-h interval. The milk N-acetyl-.beta.-D-glucosaminidase activity was elevated only in quarters infected with major pathogens. Changes of milk secretion induced by an omitted milking are affected by infection status, and additional secretory cell damage in quarters infected with a major pathogen may result from an omitted milking.