Eight primiparous cows in midlactation were used to determine a method for the mammary biopsy of standing cows in full lactation. Cows were mildly sedated; therefore, preoperative feed withdrawal was not necessary. A core of secretory tissue (0.75 to 1 g) was extracted using a rotating stainless steel cannula with a retractable blade at the cutting edge. Postoperative recovery was rapid, taking only 15 min per cow, and the method was reliable and efficient. The presence of secretory tissue was verified by histology and in situ hybridization with alpha s1-casein and alpha-lactalbumin probes. The capsular end of the core contained more connective tissue, and the parenchyma showed heterogeneous expression of alpha s1-casein and alpha-lactalbumin. Despite some postoperative bleeding, milk yield and composition in the biopsied gland were affected only transiently. Yield recovered by 3.5 d after biopsy, and composition recovered by 6.5 d after biopsy. Yield and composition of milk from the control glands were not affected by the procedure. Biopsy sites healed rapidly and without infection. No clinical mastitis was observed in any of the biopsied cows throughout the remainder of the lactation.

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A feed delivery system for the study of choice behavior in cows is described. Supportive data are provided for six dairy cows exposed to two-alternative, concurrent variable-interval schedules.Air cylind~r.

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