Milk Yield, Composition, and Somatic Cells as a Function of Time of Day in Goats Under a Continuous Lighting Regimen * *Paper No. 3913 of the Journal Series of the North Carolina State University Agricultural Experiment Station, Raleigh, North Carolina

SUMMARY Goats were milked hourly for 51 consecutive hours or at 13-hour intervals for 32 consecutive milkings. Milk production, milk fat percentage, somatic cell content, and milk serum proteins were considered as a function of time of day and infection. Milk production and milk constituents were not time-of-day dependent. Infection significantly reduced the milk produced, and increased the fat percentage and somatic cell content. Milk production and cell concentration were inversely related. Hourly milking resulted in a linear increase in milk of 0.57 ml./hour. Cell concentration decreased in a curvilinear manner. When milked at 13-hour intervals, fat percentage decreased linearly at the rate of 0.16 per cent per milking. Percentages of albumin and immuno-G-globulins increased and a-lactalbumin, b-lactoglobulin decreased in milk from infected glands. The lack of diurnal variation in milk cell content is probably explained by the facilitation of cell passage within the mammary gland by oxytocin.