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Influences of Heat Stress and Uterine Diseases on Reproduction of Dairy Cows

Wednesday, July 23, 2014: 3:30 PM
2103C (Kansas City Convention Center)
Jose E.P. Santos , Department of Animal Sciences, University of Florida, Gainesville, FL
Eduardo S. Ribeiro , Department of Animal Sciences, University of Florida, Gainesville, FL
E. Karakayan , University of Florida, Gainesville, FL
K. N. Galv„o , Department of Large Animal Clinical Sciences; University of Florida, Gainesville, FL
Fabio S. Lima , Cornell University, Ithaca, NY
Abstract Text:

Dairy cows undergo hyperthermia during the summer months in most of the world, which causes a dramatic reduction in establishment and maintenance of pregnancy. Hyperthermia has numerous effects on cellular metabolism and function that help explain reductions in fertility, including altered period of follicle dominance, reduced steroidogenic capacity of follicular and luteal cells, altered endometrial activity, and impaired oocyte quality. This multitude of effects results in reduced fertilization and influences subsequent embryo development, which impairs maintenance of pregnancy. Data are scarce on the associations between season and risk of uterine diseases in dairy cattle, but recent epidemiological studies indicate that incidence of retained placenta and metritis increases during the hot season. Therefore, it is suggested that hyperthermia during late gestation suppress the uterine defensive mechanisms, or elevated temperature and humidity during the hot months alters the environment that predisposes to increased pathogen challenge that induces disease. Unfortunately, data from studies at the University of Florida indicate that reducing hyperthermia by cooling cows during the entire dry period in the summer do not seem to alleviate the negative impacts of heat stress on metritis. It is well described that both retained placenta and metritis are important risk factors for clinical and cytological endometritis, and the multitude of diseases that affect the uterus of the cow also suppress fertility. Heat stress, but also endometrial inflammation, as observed in cows with cytological endometritis, compromises endometrial function, which can alter the secretory activity of the endometrium and lead to inability to establish and maintain pregnancy. Infection of the endometrium with Trueperella pyogenes, and likely also by other uterine pathogens, damages the superficial and glandular epithelium and increases the expression of inflammatory genes, and presence of inflammation seem to disrupt embryo development. Cows that develop uterine diseases, either metritis or cytological endometritis, have reduced fertilization, compromised early embryo development, impaired day 15 conceptus elongation, and increased risk of pregnancy loss. The day 15 conceptus of cows with metritis have marked changes in gene expression, and hyperthermia (in vivo or in vitro)dramatically alters mRNA expression of early embryos, and these changes might explain the differences in maintenance of pregnancy in cows that suffer from uterine diseases or heat stress. Collectively, heat stress directly and negatively impacts reproduction while also increasing the risk of uterine diseases that further depress the establishment and maintenance of pregnancy in dairy cows.

Keywords: Heat Stress, Reproduction Physiology, Endometritis