Obesity is associated with altered metabolic and reproductive activity in the mare: effects of metformin on insulin sensitivity and reproductive cyclicity.
Abstract: In mares, obesity is associated with continuous reproductive activity during the non-breeding season. To investigate the effect of obesity and associated alterations in metabolic parameters on the oestrous cycle, two related studies were conducted. In Experiment 1, obese (body condition score > 7) mares were fed ad libitum or were moderately feed restricted during the late summer and autumn months. Feed restriction did not alter the proportion of mares entering seasonal anoestrus. However, obese mares exhibited a significantly longer duration of the oestrous cycle, significant increases in circulating concentrations of leptin and insulin, and decreased insulin sensitivity and concentrations of thyroxine compared with feed-restricted mares throughout the experiment. Experiment 2 was designed to investigate the effects of administration of the insulin-sensitising drug metformin hydrochloride on insulin sensitivity and the characteristics of the oestrous cycle in obese mares. In a dose-response trial, metformin increased insulin sensitivity after 30 days following administration of 3 g day(-1), but not 6 or 9 g day(-1), compared with controls receiving vehicle only. However, there were no differences in insulin sensitivity or oestrous cycle characteristics between control and metformin-treated groups when the 3 g day(-1) dose was tested for a longer period of 2 months. These results demonstrate that obesity is associated with aberrations in the oestrous cycle and perturbations in several markers of metabolic status. The results also indicate that metformin is not an effective long-term monotherapy for increasing insulin sensitivity in horses at the doses tested. Additional studies are needed to examine possible effects of increasing insulin sensitivity on reproductive activity in obese mares.
Publication Date: 2006-08-26 PubMed ID: 16930507DOI: 10.1071/rd06016Google Scholar: Lookup
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- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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The research article discusses two studies that explore the impact of obesity on the reproductive activity and metabolism in mares, and the effectiveness of metformin, an insulin-sensitising drug, in addressing these issues. It was found that while metformin can initially increase insulin sensitivity, it did not prove to be an effective long-term treatment.
Two-Study Research on Obesity and Metformin Use in Mares
This paper primarily focuses on understanding the effect of obesity on the reproductive and metabolic process in mares, and how metformin, a generally used insulin-sensitising drug, can be used to counter some of the obesogenic effects. It explains the results of two closely related experimental studies on obese mares carried out to understand these aspects.
- Experiment 1: The researchers studied the effect of uncontrolled feeding versus controlled feeding on obese mares during the late summer and autumn months. The aim was to learn how it influenced the oestrous cycle.
- Experiment 2: The team evaluated how metformin impacted insulin sensitivity and the oestrous cycle in obese mares.
Findings and Implications
Several key findings were derived from these studies, which further elucidate the relationship between obesity, metabolism, and reproduction in mares.
- In the first study, it was observed that feed restriction did not alter the tendency of mares to enter a state of quiescence in reproductive activity, termed as ‘seasonal anoestrus’.
- However, obese mares displayed a longer duration of the oestrous cycle compared to those with feed restrictions.
- In terms of metabolic changes, obese mares had significant increases in circulating concentrations of leptin and insulin and decreased insulin sensitivity.
- Interestingly, in the second study, metformin appeared to boost insulin sensitivity in the short term. However, over a more extended period (two months), it failed to exhibit significant improvements in insulin sensitivity or oestrous cycle traits.
The article concludes by stressing that obesity does affect the oestrous cycle and metabolism of mares. However, metformin does not seem to be an effective long-term solution at the doses tested. Further research is needed to explore the implications of improved insulin sensitivity on the reproductive behaviour of obese mares.
Cite This Article
APA
Vick MM, Sessions DR, Murphy BA, Kennedy EL, Reedy SE, Fitzgerald BP.
(2006).
Obesity is associated with altered metabolic and reproductive activity in the mare: effects of metformin on insulin sensitivity and reproductive cyclicity.
Reprod Fertil Dev, 18(6), 609-617.
https://doi.org/10.1071/rd06016 Publication
Researcher Affiliations
- Department of Veterinary Science, Maxwell Gluck Equine Research Center, University of Kentucky, Lexington, KY 40546, USA.
MeSH Terms
- Animals
- Breeding
- Dose-Response Relationship, Drug
- Estrous Cycle
- Female
- Food Deprivation
- Horse Diseases / drug therapy
- Horse Diseases / physiopathology
- Horses
- Hypoglycemic Agents / administration & dosage
- Insulin / blood
- Insulin Resistance
- Leptin / blood
- Metformin / administration & dosage
- Obesity / complications
- Obesity / physiopathology
- Obesity / veterinary
- Reproduction
- Seasons
- Thyroxine / blood
Citations
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