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Histology, Cytology, and Size of the Parathyroid in Bovine Related to Age and Function¹

Department of Dairy Science, The University of Arizona, Tucson

ABSTRACT

The weight of bovine parathyroids, along with the histological and cytological changes that occur in them throughout lactation and the reproductive cycle, have been studied. Results indicate that there are cyclic changes that occur in the activity of the parathyroid which correspond with the annual mineral metabolism cycle of the dairy cow.

During heavy lactation, the glands are depressed in secretory activity, as indicated by their smaller size. The tissue is composed of small chromophilic cells containing massive aggregations of sudanophilic granules and vesicles. A gradual change occurs after mid-lactation to increase gland size. Deposition of fatty tissue within the gland capsule and a change in cytology to cells (principal cells) devoid of the aggregated sudanophilic granules and vesicles is evident.

Just prior to parturition the parathyroids show evidence of the greatest secretory activity. The tissue hypertrophies, resulting in larger glands composed of large clear cells.

¹ Many of these data are parts of a thesis presented by the senior author to the University of Wisconsin in partial fulfillment of the requirements of a Ph.D. degree. Further work has been completed at The University of Arizona, supported in part by a grant from The National Institutes of Health. Published with the approval of the Director of the Wisconsin Agricultural Experiment Station. Arizona Agricultural Experiment Station, Technical Paper No. 873.