Format:

Author:

Lord, Lindsay Elizabeth

Title:

Effect of photoperiod treatment on expression of genes related to immune function in dairy cattle

Dept./Program:

Animal Sciences

Year:

2009

Degree:

MS

Abstract:

Maximizing efficiency is essential to profitability of livestock production systems. Thus, there is a need for effective, low-cost tools that can increase production efficiency. Manipulation of photoperiod (PP), which is defined as an animal's daily exposure to light, is a management practice that can elicit beneficial production responses at minimal cost. Long day PP treatment (LD; 16 h light: 8 h dark) increases growth in heifers and milk yield in lactating dairy cattle. Short day PP treatment (SD; 8 h light: 16 h dark) increases subsequent milk yield and enhances immune function in dry cows. Skeletal photoperiod treatment involves the application of brief pulses of light at specific times to mimic exposure to LD and elicit similar physiological responses despite a drastic reduction in number of light hours per day. The goals of this research were to determine effects of photoperiod treatments on expression of immune function-related genes and to assess their potential as means to enhance immune function and production efficiency.
Based on a preliminary microarray experiment, a list of genes that were differentially expressed in response to PP treatment was generated. From that list, several immune finction-related genes were selected: indoleamine 2,3-dioxygenase (IDO), major histocompatibility complex class I (MHC), lipopolysaccharide binding protein (LBP), ephrin B6 receptor (EphB6), and dentin matrix acidic phosphoprotein 1 (DMP1). Although they were not differentially expressed in the microarray experiment, we also selected β-2 microglobulin (B2M) and the long form of the prolactin receptor (PRL-R) because expression of these genes is known to be related to immune function and changes in photoperiod treatment.
The first research trial revealed that average daily expression of IDO, MHC, and LBP in peripheral blood mononuclear cells of prepubertal heifers was not different between SD and LD treatment, despite markedly different daily expression patterns for ID0 and MHC. Plasma concentrations of melatonin (MEL) were higher during periods of darkness than during periods of light, but secretion of MEL did not correlate with expression of any of the above genes. Comparison of LD photoperiod treatment to skeletal LD treatment revealed that overall there were no differences in average secretion of MEL or in expression of any of the genes, suggesting that these treatments had similar effects. In summary, these data imply that although circadian changes in immune function-related gene expression could influence disease susceptibility, MEL does not appear to regulate the response. Furthermore, skeletal photoperiod treatment has promise as a potential management tool that may positively influence animal physiology while minimizing the need for, and expense of, supplemental lighting.
A second experiment investigated the effects of PP treatment on expression of immune function-related genes in mammary gland samples fiom dry cows exposed to either LD or SD photoperiod treatment. Results revealed no difference in expression of any of the above genes in response to LD or SD. Further research is needed to determine specific changes in gene expression, physiological function and animal health in response to PP treatment and to develop novel methods for enhancing production efficiency.