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Factors Affecting Intramammary Pressures

Department of Dairy Science, Virginia Polytechnic Institute, Blacksburg

ABSTRACT

Intramammary pressures were measured on 12 Holstein cows during the AM and PM milkings at monthly intervals during the lactation period. Prestimulation pressure averaged 21.9 mm Hg at the AM milking and 15.8 mm Hg at the PM milking. Poststimulation pressures were also highest at the AM milking with the rear quarters exhibiting pressures of 42.7 and 42.2 mm Hg and the fore quarters 34.8 and 34.2 mm Hg. During the PM milking, pressures of 34.9 and 34.3 mm Hg were observed in the rear quarters and 28.3 and 27.9 mm Hg in the fore quarters. After-milking pressures ranged from 3.1 to 3.8 mm Hg.

Milk yields were greater at the AM milking, and in the rear quarters at all milkings. Level of intramammary pressures for each quarter was related to the amount of milk produced at each milking. Month of lactation had a marked negative effect on pressures as indicated by correlations ranging from –.70 to –.88.

¹ Present address: Department of Animal Science, Cornell University, Itliaca.