Photoperiodic Effects on Immune Function in Dairy Cattle: Potential Mediation Through Prolactin and Its Receptor

Photoperiod management is known to affect physiological changes in many species. These experiments were designed to examine physiological effects of photoperiod on dairy cattle, with particular emphasis on the immune system. The mechanism whereby photoperiod alters immune function was also investigated. The experiments in Chapter 1 determined a positive effect of short day photoperiod treatment, relative to long day photoperiod treatment, on lymphocyte proliferation of Holstein steers. Use of bromocriptine to reduce circulating prolactin in animals on a long day photoperiod increased lymphocyte proliferation and neutrophil chemotaxis to levels observed in short day photoperiod treated animals. The experiments described in Chapters 2 and 3 examined the effects of photoperiod treatment during the dry period of multiparous Holstein cows. Dry matter intake during the dry period was increased in cows on short day photoperiod treatment, as was subsequent milk production, relative to long day treatment. Neutrophil chemotaxis and lymphocyte proliferation were enhanced by short day treatment during the dry period and postpartum. In addition, short day treated cows had reduced incidence of mastitis and retained placenta relative to long day treated cows and had lower somatic cell counts throughout their subsequent lactation. The experiment in Chapter 4 revealed that administration of exogenous prolactin to short day treated steers increased prolactin concentrations similar to those of long day treated animals, but decreased the lymphocyte proliferation and neutrophil chemotaxis of these animals. Throughout all of the experiments, prolactin concentrations and prolactin receptor expression were inversely related in all of the tissues examined, regardless of age, sex, reproductive status of the animals, or method of manipulation of circulating prolactin concentrations. In conclusion, short day photoperiod treatment improves immune function in dairy cattle, compared to animals receiving long day photoperiod treatment, and this change in immunophysiology is mediated through changes in prolactin and its receptor.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Animal Sciences

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2015

Author dc:creator

• Auchtung, Tera Lynne

Contributors dc:contributor

• Dahl, Geoffrey E.

• Agriculture, Animal Culture and Nutrition

Language dc:language

eng

Identifier

(MiAaPQ)AAI3111520

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/83562