Aspects of lactation endocrinology: I. lactogenic receptors in bovine mammary tissue at different stages of lactation: II. growth hormone concentrations in Holstein cattle of differing genetic merit

Mammary tissue from nine Holstein cows was collected within one week of parturition, at 60 and 180 days postpartum. Blood samples were collected at 6-hr intervals from two days prior to . until two days after surgery. A membrane-enriched fraction of tissue homogenates was prepared by differential centrifugation. Displacement curve data was analyzed by a microcomputer program. Mean prolactin (Prl) during the periparturient period was greater than either postpartum period, but not prior to biopsy. Dissociation constants (Kd) estimated with NIH-bPRL-6 as competitor were not different among stages of lactation, and averaged 8.97 x 10⁻⁸M. Receptor concentrations were less during _the periparturient period than later lactation. The Kd was 100-fold greater when estimated with human growth hormone as competitor. It is concluded that lactogenic hormone receptor concentrations in bovine mammary tissue increase with the onset of lactation, following a pattern similar to that observed in non-ruminants. Three experiments were conducted to investigate endocrine metabolic hormone profiles in Holstein cattle of differing genetic merit at several ages. Control animals were randomly bred to non-AI sires originating in the Virginia Tech Dairy herd. Selected animals were offspring of commercially available AI sires. In one experiment, mean plasma Prl was greater in control animals after feeding and insulin injection, while growth hormone (GH) was greater in selected animals at all ages. Free fatty acids were greater in selected animals at 6 and 24 months of age, while glucose (Glc) and urea were unaffected by genetic merit. In a second experiment, Holstein bull calves were administered Glc and thyrotropin releasing hormone (TRH) on different days. Plasma GH was greater in selected animals. Plasma Prl was greater in control animals after TRH. In the third experiment, Holstein cows received TRH at 30, 90 and 200 days postpartum (DPP). Net energy balance was negative at 30, while positive at 90 and 200 DPP. Plasma GH before and after TRH was greater in selected animals, and greater during early than later lactation. Thus, the results of the three experiments indicate that increased plasma GH may be associated with selection for increased milk yield.

Name thesis:degree_name

Ph. D.

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Animal Science

Department dc:contributor.department

Animal Science

Grantor dc:publisher

Virginia Polytechnic Institute and State University

Year dc:date.issued

1985

Author dc:creator

• Kazmer, Gary Wayne

Chair dc:contributor.committeechair

• Barnes, M.A.

Committee members dc:contributor.committeemember

• Akers, Robert Michael
• Denbow, D. Michael
• Keenan, Thomas W.
• Pearson, R.E.

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en_US

Handle dc:identifier.uri

http://hdl.handle.net/10919/52298

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/52298