1. Estrous Cycle Characteristics
Effect of age on circulating inflammatory markers during luteal and follicular phases of the equine estrous cycle
RD Jacobs*1, RM Brooks2, JA Brown3, SA Willmott1, TD Stephens1 and RK Splan1
1Virginia Polytechnic Institute and State University, Blacksburg, VA; 2 Colorado State University, Fort Collins, CO; 3 Marion DuPont Scott Equine Medical Center, Leesburg, VA
Background
Methods
Results
Results
Peak fertility in horses occurs between 6 to 7 years of age
Foaling rates decline in older mares due to reproductive aging and early embryonic death
Decreased fertility is a common challenge in breeding older mares
Aging process is associated with increases in local and systemic levels of pro-inflammatory cytokines
Elevated pro-inflammatory cytokines may mediate:
Steroidogenesis
Ovulation
Establishment of early pregnancy
Pro-inflammatory cytokines
Tumor necrosis factor (TNF)-α
Interleukin (IL)-6
Anti-inflammatory cytokines
Interleukin (IL)-10
Ultrasound
Mares were evaluated once daily by transrectal ultrasound to determine day of ovulation
Ovulation was confirmed by presence of corpus luteum
Blood Collection
Blood was collected via jugular venipuncture:
Every 2 days post ovulation for progesterone analysis
Every 3 days post ovulation for cytokine analysis
Day 0, mid- and end- cycle for complete blood count
Statistical Analysis
All data were analyzed using SAS (Version 9.2, SAS Institute Inc., Cary, NC)
Percent double ovulation was analyzed using the Fisher’s Exact Test
Luteal phase duration and estrous cycle duration were analyzed using the Wilcoxon-Mann-Whitney Test
IL-10 during both luteal and follicular phases was transformed (sqrt(x)) to meet normality assumptions
Estrous Cycle Characteristics a a
Measurement
Aged
Adult
P-Value
Double Ovulation (%)
60.00±24.50
16.67±16.67
0.242
Luteal Phase Length (d)
18.20±0.49
18.33±0.42
0.913
Estrous Cycle Length (d)
24.00±0.55
23.00±0.82
0.505 a a
Figure 3- IL-6 concentrations in luteal and follicular phases of the estrous cycle in aged vs. adult mares
Table 1- Estrous cycle dynamics in aged vs. adult mares
Cytokines
Implications a a
Better understanding of the role of inflammatory profiles in relation to age could lead to effective therapies to improve reproductive efficiency
Improving reproductive capacity of older mares would benefit the equine industry as a whole
The horse may be a suitable model for reproductive aging in humans
Elucidation of relationships between pro-inflammatory cytokines and reproductive efficiency is important in human health
Offspring health in relation to mare age and inflammatory status is an important and exciting area of new research
Further exploration of tissue-specific cytokine production may assist in developing therapies to reduce inflammatory mediators to improve reproductive efficiency in aged mares b b
Figure 1- TNFα concentrations in luteal and follicular phases of the estrous cycle in aged vs. adult mares. Differing superscripts indicate significant difference (P<0.05)
Objective
The objective of this study was to to examine the effect of age on pro- and anti- inflammatory cytokine levels during the normal estrous cycle of the horse. a a
Methods
Animals and Diet
Eleven mares from aged (n=5; mean ± SEM, 20.2 ±1.24 yr) and adult (n=6; mean ± SEM, 7.3 ± 1.14 yr) age classes were used
Mares were housed on a single pasture and had ad libitum access to mixed fescue and orchardgrass
Mares had ad libitum access to water and mineral/vitamin mix formulated for horses
Project Timeline b b
Luteal
Follicular
d 0
~d 14
Funding Statement
Figure 2- IL-10 concentrations in luteal and follicular phases of the estrous cycle in aged vs. adult mares. Differing superscripts indicate significant difference (P<0.05)
This study was funded by the Virginia Horse Industry Board