High versus low body condition in mares: interactions with responses to somatotropin, GnRH analog, and dexamethasone.
Abstract: Mares that had previously been fed to attain body condition scores (BCS) of 7.5 to 8.5 (high) or 3.0 to 3.5 (low) were used to determine the interaction of BCS with the responses to 1) administration of equine somatotropin (eST) daily for 14 d beginning January 20 followed by administration of GnRH analog (GnRHa) daily for 21 d and 2) 4-d treatment with dexamethasone later in the spring when mares in low BCS had begun to ovulate. The majority of mares with high BCS continued to cycle throughout the winter, as evidenced by larger ovaries (P < 0.002), more corpora lutea (P < 0.05), greater progesterone concentrations during eST treatment (P < 0.04), and more (P < 0.05) large- and medium-sized follicles. Treatment with eST alone or in combination with GnRHa had no effect (P > 0.05) on ovarian activity or ovulation. Plasma leptin concentrations were greater (P < 0.002) in mares with high BCS; however, there was no effect (P > 0.10) of eST treatment. Plasma IGF-I concentrations were greater (P < 0.0001) in mares treated with eST compared with mares given vehicle, and mares with high BCS had greater IGF-I (P < 0.02) and LH concentrations (P < 0.02) than mares with low BCS. Plasma leptin concentrations in mares with high BCS were increased (P < 0.001) within 12 h of dexamethasone treatment; the leptin response (P < 0.001) in mares with low BCS was greatly reduced (P < 0.001) and transient. Glucose and insulin concentrations also increased (P < 0.0001) after dexamethasone treatment in both groups, and the magnitude of the response was greater (P < 0.0001) in mares with high BCS than in mares with low BCS. In summary,low BCS in mares was associated with a consistent seasonal anovulatory state that was affected little by eST and GnRHa administration. In contrast, all but one mare with high BCS continued to experience estrous cycles and(or) have abundant follicular activity on their ovaries. The IGF-I response to eST treatment was also reduced in mares with low BCS, as was the basal leptin concentration and leptin response to dexamethasone. Although low BCS and leptin concentrations were associated with inactive ovaries during winter and early spring, mares with low BCS eventually ovulated in April and May while leptin concentrations remained low.
Publication Date: 2003-01-25 PubMed ID: 12542169DOI: 10.2527/2002.80123277xGoogle Scholar: Lookup
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- Journal Article
Summary
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The research examined how the body condition of mares, either high or low, interacted with their responses to different types of hormonal treatment. The study found that mares with a high body condition score continued to ovulate throughout winter and had higher levels of certain hormones. Conversely, mares with a low body condition score exhibited lower concentrations of these hormones and experienced seasonal non-productivity, which was not significantly impacted through hormonal treatment.
Research Methodology
- The researchers took mares that had been fed to achieve either high (7.5 to 8.5) or low (3.0 to 3.5) body condition scores (BCS).
- These mares underwent two different treatments; the first involved administering equine somatotropin (eST) daily for 14 days followed by a daily dose of GnRH analog (GnRHa) for 21 days. The second treatment involved a 4-day course of dexamethasone in the spring, once the low BCS mares had started to ovulate.
Findings for High BCS Mares
- Mares with high BCS had enlarged ovaries, more corpora lutea (a temporary structure involved in the female menstrual cycle), and greater progesterone levels during eST treatment. They also exhibited more large and medium-sized follicles, meaning they continued to cycle throughout winter seasons.
- High BCS mares also had higher leptin concentrations, with a marked increase after dexamethasone treatment.
- Conversely, the administration of eST alone or combined with GnRHa did not seem to affect the ovarian activity or ovulation of the mares.
- High BCS mares presented greater concentrations of plasma IGF-I (a hormone that enhances insulin secretion and insulin action) when treated with eST and had greater IGF-I and LH (luteinizing hormone) concentrations than mares with low BCS.
- Insulin and glucose levels also increased after dexamethasone treatment, with high BCS mares showing a greater response.
Findings for Low BCS Mares
- Low BCS mares were characterized by a seasonal non-productivity state that was relatively unaffected by the hormonal treatments (eST and GnRHa).
- The leptin response in low BCS mares to dexamethasone treatment was significantly reduced and transient compared to their high BCS counterparts.
- Low BCS mares presented a diminished IGF-I response to eST treatment and lower baseline concentrations of leptin.
- Despite their inactive ovaries during winter and early spring, mares with low BCS eventually began ovulating in late spring (April and May), even though their leptin concentrations remained low.
Cite This Article
APA
Gentry LR, Thompson DL, Gentry GT, Davis KA, Godke RA.
(2003).
High versus low body condition in mares: interactions with responses to somatotropin, GnRH analog, and dexamethasone.
J Anim Sci, 80(12), 3277-3285.
https://doi.org/10.2527/2002.80123277x Publication
Researcher Affiliations
- Department of Animal Science, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge 70803-4210, USA.
MeSH Terms
- Animals
- Blood Glucose / analysis
- Dexamethasone / pharmacology
- Estrus / physiology
- Female
- Gonadotropin-Releasing Hormone / analogs & derivatives
- Gonadotropin-Releasing Hormone / pharmacology
- Growth Hormone / pharmacology
- Horses / physiology
- Insulin / blood
- Insulin-Like Growth Factor I / analysis
- Leptin / blood
- Ovarian Follicle
- Ovulation / drug effects
- Ovulation Induction / veterinary
- Seasons
- Time Factors
Citations
This article has been cited 3 times.- Song Y, Jiang X, Hao Y, Sun R, Bai Y, Xu C, Xia C. Comprehensive serum, follicular fluid, and ovarian tissue profiling reveals systemic metabolic alterations in high-yielding dairy cows with postpartum inactive ovaries. BMC Vet Res 2026 Jan 5;22(1):2.
- Song Y, Cheng J, Yu H, Wang Z, Bai Y, Xia C, Xu C. Early Warning for Ovarian Diseases Based on Plasma Non-esterified Fatty Acid and Calcium Concentrations in Dairy Cows. Front Vet Sci 2021;8:792498.
- Salazar-Ortiz J, Camous S, Briant C, Lardic L, Chesneau D, Guillaume D. Effects of nutritional cues on the duration of the winter anovulatory phase and on associated hormone levels in adult female Welsh pony horses (Equus caballus). Reprod Biol Endocrinol 2011 Sep 29;9:130.
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