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.

Plasma concentration of leptin and ghrelin in Standardbred foals as related to the age, sex, exercise and training

“…The study of stud mares indicated the tendency to decrease in plasma leptin concentration in the period from summer to winter and the same trends were seen in values of BW and percent of body fat mass (Gentry et al, 2002;Buff et al, 2007). However, these results were obtained in animals that were not exercised.…”

“…High standard deviations are typical for horses in good body condition and can be explained by genetic heterogeneity (Gentry et al, 2002). The physical effort the investigated trotters were submitted to was typical for daily training session.…”

“…This information is not fully supported in the study of horses (Buff et al, 2002). The studies of mares suggest that leptin may be an important link between nutrition and reproductive status (Gentry et al, 2002). Leptin can also play an important role in the -E-mail: witold.kedzierski@ar.lublin.pl regulation of lipid metabolism during the periparturient period (Kędzierski et al, 2008).…”

Changes in plasma leptin concentration during different types of exercises performed by horses

“…Generally, plasma leptin level correlates positively with body fat mass (Gentry et al, 2002;Kearns et al, 2006) and plasma triacylglycerol (TG) concentration as well as with the age of horses (Buff et al, 2005;Gordon et al, 2007a;Čebulj-Kadunc et al, 2009). The synthesis of leptin is stimulated by insulin and corticosteroids, whereas catecholamines play an inhibiting role in the leptin synthesis (Meier and Gressner, 2004).…”

A study of serum insulin-like growth factor type 1 (IGF-1) concentrations in resting untrained Andalusian horses: influence of age and gender

“…We did not score body condition in the studied horses, this being a point of limitation in our research, and although we measured some indicators of body size, such as HW and DTx, the animals were not weighed. Gentry et al (2002) reported that circulating IGF-1 concentrations tended to be higher in mares with higher body condition score.…”