The relationship between body condition, leptin, and reproductive and hormonal characteristics of mares during the seasonal anovulatory period.
Abstract: An experiment was conducted to determine the effects of high vs low body condition scores (BCS) produced by restricted feeding on reproductive characteristics, hormonal secretion, and leptin concentrations in mares during the autumnal transition and winter anovulatory period. Mares with BCS of 6.5 to 8.0 were maintained on pasture and/or grass hay, and starting in September, were full fed or restricted to produce BCS of 7.5 to 8.5 (high) or 3.0 to 3.5 (low) by December. All but one mare with high BCS continued to ovulate or have follicular activity during the winter, whereas mares with low BCS went reproductively quiescent. Plasma leptin concentrations varied widely before the onset of restriction, even though all mares were in good body condition. During the experiment, leptin concentrations gradually decreased (P < 0.0001) over time in both groups, but were higher (P < 0.009) in mares with high vs low BCS after 6 wk of restriction, regardless of initial concentration. No differences (P > 0.1) between groups were detected for plasma concentrations of LH, FSH, TSH, GH, glucose, or insulin in samples collected weekly; in contrast, plasma prolactin concentrations were higher (P < 0.02) in mares with high BCS, but also decreased over time (P < 0.008). Plasma IGF-I concentrations tended (P = 0.1) to be greater in mares with high vs low BCS. The prolactin response to sulpiride injection on January 7 did not differ (P > 0.1) between groups. During 12 h of frequent blood sampling on January 12, LH concentrations were higher (P < 0.0001), whereas GH concentrations (P < 0.0001) and response to secretagogue (EP51389; P < 0.03) were lower in mares with high BCS. On January 19, the LH response to GnRH was higher (P < 0.02) in mares with high BCS; the prolactin response to TRH also was higher (P < 0.01) in mares with high BCS. In conclusion, nutrient restriction resulting in low BCS in mares resulted in a profound seasonal anovulatory period that was accompanied by lower leptin, IGF-I, and prolactin concentrations. All but one mare with high BCS continued to cycle throughout the winter or had significant follicular activity on the ovaries. Although leptin concentrations on average are very low in mares with low BCS and higher in well-fed mares, there is a wide variation in concentrations among well-fed mares, indicating that some other factor(s) may determine leptin concentrations under conditions of high BCS.
Publication Date: 2002-11-05 PubMed ID: 12413093DOI: 10.2527/2002.80102695xGoogle Scholar: Lookup
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Summary
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The research article investigates the effect of body condition scores (BCS) influenced by two different feeding regimes (full feeding and restricted feeding), on the reproductive characteristics, hormonal secretion, and leptin concentrations in mares during their autumnal transition and winter anovulatory period.
Study Design
- The experiment was designed to determine how varying body condition scores (BCS), produced by different feeding amounts, affect the hormonal and reproductive characteristics of mares. Mares with initial scores ranging from 6.5 to 8.0 were put on different feeding regimes starting from September, intending to produce high BCS (7.5 – 8.5) or low BCS (3.0 – 3.5) by December.
- Various physiological factors were monitored throughout the experiment, including ovulation/follicular activity, plasma leptin concentrations, and the concentrations of several hormones including LH (luteinizing hormone), FSH (follicle-stimulating hormone), TSH (thyroid-stimulating hormone), GH (growth hormone), prolactin, IGF-I (insulin-like growth factor I), insulin, and glucose.
- In addition, the hormonal response to certain treatments, such as sulpiride injection and GnRH (gonadotropin-releasing hormone), were assessed in January.
Results
- All but one mare with high BCS continued to have ovarian activity during winter. Conversely, mares with low BCS entered reproductive dormancy.
- Before feeding restrictions began, leptin levels widely varied, despite all mares being in good condition. Over time, leptin levels slowly decreased in both groups, more so in the mares with high BCS after six weeks of restriction, regardless of the initial concentration.
- Regarding other hormonal levels, there were no significant differences detected between the two groups for LH, FSH, TSH, GH, glucose, or insulin. However, mares with a higher BCS showed higher plasma prolactin concentrations which also decreased over time.
- The prolactin response to sulpiride injection did not differ between the two groups, While LH concentrations were higher with high BCS mares, GH response was lower.
- Higher hormonal responses were observed in the high BCS group: LH response to GnRH and prolactin response to TRH (thyrotropin-releasing hormone) were significantly higher.
Conclusion
- The study concluded that nutrient restriction leading to low BCS resulted in an intensified seasonal anovulatory period in mares, accompanied by lower leptin, IGF-I, and prolactin concentrations.
- On the other hand, mares with high BCS, excluding one, continued to cycle throughout the winter or had significant follicular activity.
- However, the observed wide variation in leptin concentrations among well-fed mares suggests other factor(s) may determine leptin concentrations under conditions of high BCS, thereby necessitating further research.
Cite This Article
APA
Gentry LR, Thompson DL, Gentry GT, Davis KA, Godke RA, Cartmill JA.
(2002).
The relationship between body condition, leptin, and reproductive and hormonal characteristics of mares during the seasonal anovulatory period.
J Anim Sci, 80(10), 2695-2703.
https://doi.org/10.2527/2002.80102695x Publication
Researcher Affiliations
- Department of Animal Science, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge 70803-4210, USA.
MeSH Terms
- Animals
- Body Constitution / physiology
- Dopamine Antagonists / pharmacology
- Female
- Fertility Agents, Female / pharmacology
- Follicle Stimulating Hormone / blood
- Gonadotropin-Releasing Hormone / pharmacology
- Growth Hormone / blood
- Health Status
- Horses / blood
- Horses / physiology
- Insulin-Like Growth Factor I / metabolism
- Leptin / blood
- Luteinizing Hormone / blood
- Oligopeptides / pharmacology
- Ovulation / physiology
- Prolactin / blood
- Random Allocation
- Seasons
- Sulpiride / pharmacology
- Thyrotropin-Releasing Hormone / pharmacology
- Time Factors
Citations
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