Variations of plasma leptin in show horses during a work season

Abstract

Leptin is an adipocytokine mainly expressed by adipose tissue. Secretion of leptin in healthy animals is closely related to fat mass and metabolic activity. The aim of this study was to investigate plasma leptin variations, in relation to nutritional and exercise parameters in adult show horses during a work season. EDTA-blood samples were taken at rest from 37 Iberian horses. Body weight, body condition score and fat percentage determined by ultrasonic measurement of rump fat thickness were measured. Plasma leptin was determined with a multi-species RIA kit. Linear mixed effects model was used to assess relationship between plasma leptin and other biological parameters. Plasma leptin concentration was <12.6 ng/ml (mean = 2.8 ± 1.6 ng/ml) and was significantly higher during training periods (p < 0.0001) (4.5 ± 1.7 ng/ml) than in show periods (2.0 ± 1.1 ng/ml), despite a significant increase (p < 0.0001) in energy intake. The body weight remained almost constant. The plasma leptin concentrations were significantly affected by exercise (p < 0.0001), body weight (p = 0.04) and BCS (p < 0.0001), but were not affected by percentage of fat. In conclusion, the marked decrease in leptin values observed during a period of intense (i.e. excessive) exercise could result from an adaptation to cumulative alterations in energy balance, to exercise per se or to a combination of both.

Long‐term leptin fluctuations in female donkeys

“…The study of Diez et al [21] was performed in donkeys of both genders (41 females, 9 males) aged 7.8 ± 5.3 years, kept in small paddocks. This could explain higher leptin concentrations in these donkeys than in our jennies, as higher serum leptin concentrations were also reported in geldings and stallions than in mares [14] and in older than in younger horses [14], while a marked decrease of leptin concentrations was observed in horses during periods of intensive exercise [30]. Patterns of feeding, feed composition and availability are significant factors which influence leptin concentrations in horses [31][32][33] and could have also contributed to lower leptin concentrations in these jennies when compared with donkeys in another study [21], which were fed grass supplemented with hay and/or concentrate.…”

“…A significant rise of leptin levels in these jennies was observed at times of transition to pasture. During this period, ingestion of young vegetation, rich in carbohydrates, is reported to increase serum leptin concentrations in equines . The transition to pasture could also represent a stressful condition for previously stabled animals, promoting glucocorticoid secretion, which has been shown to stimulate leptin secretion .…”

“…The transition to pasture could also represent a stressful condition for previously stabled animals, promoting glucocorticoid secretion, which has been shown to stimulate leptin secretion . In contrast, the lowest leptin values have been found in mares when consuming hay , which may explain the lower leptin values in these jennies while stabled. The gradual decrease of leptin values in summer and autumn months can also be attributed to the reduction of feed quality caused by drought, which is a recurring problem in the dry Mediterranean karst grasslands .…”

“…However, peak leptin values in jennies were found 3-4 months earlier than in fillies, indicating various mechanisms of leptin regulation in both species, which could include influences of melatonin secretion on leptin sensitivity [3]. Another explanation for the differences between donkeys and horses could be various feeding-housing regimens, which have been reported to influence leptin secretion in horses [30]. Circulating leptin concentration in all groups of jennies followed a seasonal pattern, which correlated significantly with the annual changes of photoperiod in moderate latitudes (Fig 2).…”

Seasonal fluctuations in body weight during growth of Thoroughbred racehorses during their athletic career

“…Body weight change depends on energy balance, which is defined as the relationship between energy intake and energy expenditure [ 26 , 27 ]. This applies to horses [ 28 ]. The energy intake of Przewalski horses, which were originally wild herbivores of Central Asia, peaks in autumn and reaches its nadir in late winter [ 4 ], whereas energy expenditure is particularly low in winter compared with that in spring and summer [ 5 ].…”