Hormonal patterns in normal and hyperleptinemic mares in response to three common feeding-housing regimens1

Abstract

We previously reported that a rise in plasma leptin concentrations followed the rise in insulin and glucose in meal-fed horses, whereas horses maintained on pasture had little fluctuations in hormonal patterns. We have also described a hyperleptinemic-hyperinsulinemic condition that occurs in about 30% of our light horse mares of high body condition maintained on pasture. The present experiment was designed to 1) study the effect of 3 common feeding-housing regimens on leptin and other metabolic hormones in mares and 2) determine whether the hyperleptinemic condition interacted with these regimens. Six light horse mares with high body condition (average score = 7) were assigned to 2 simultaneous 3 x 3 Latin squares, 1 with normal mares (leptin = 0.1 to 6 ng/mL) and 1 with mares displaying hyperleptinemia (>10 ng/mL). Three feeding-housing regimens were compared: ad libitum pasture, ad libitum native grass hay in an outdoor paddock, and single morning feedings of a pelleted concentrate and hay at 0700 in a barn. Five days of acclimation to the feeding regimens were followed by a 36-h period of hourly blood collection to characterize the hormonal characteristics. Leptin concentrations were elevated (P < 0.001) in mares predetermined to be hyperleptinemic compared with normal mares, regardless of the feeding regimen. Leptin was greatest (P < 0.01) in mares on pasture and least in mares fed hay. Variations over time (P < 0.01) were present for all hormones and metabolites studied. Glucose and insulin concentrations were greatest (P < 0.01) in mares on pasture, with meal-fed mares exhibiting an immediate rise in plasma concentrations of both after feeding. Mares on hay had low and constant concentrations of glucose, insulin, and leptin, with no apparent fluctuations. Cortisol, prolactin, and IGF-I did not differ with leptin status, whereas GH differed due to feeding-housing regimen (P < 0.02); there was also an interaction of leptin status and feeding-housing regimen for GH concentrations (P = 0.094). It was concluded that 1) estimates of hormonal secretion in horses based on frequent sampling, depending upon the hormone in question, can be profoundly affected by the feeding-housing regimens, and 2) the hyperleptinemic condition persists under differing conditions of feeding-housing.

Prevalence and risk factors for hyperinsulinaemia in ponies in Queensland, Australia

“…Supplementary feeding increased the risk of hyperinsulinaemia by almost 5‐fold. Insulin concentrations have been shown to increase after feeding concentrates and remain elevated for 6–8 h . Although the ponies in this study had concentrates withheld on the morning of sampling, supplementary feeding of ponies with concentrate feed is likely to result in obesity and thus contribute to the development of IR, and many owners identified feeding of grain as a perceived risk factor for laminitis.…”

Prolactin in the Horse: Historical Perspective, Actions and Reactions, and Its Role in Reproduction

“…However, the effect of reduced feed intake or lack thereof on prolactin secretion was directly tested by a second experiment described by Nadal et al [71], which revealed that total feed deprivation of mares for 72 hours did not alter prolactin concentrations in daily blood samples. Similarly, a feeding regimen of dried grass hay in a dry lot [73] did not alter prolactin concentrations in mares compared with when they were on pasture 24 hours per day (ad libitum grazing). For comparison, the dried hay-dry lot regimen reduced average insulin, leptin, and IGF-I concentrations dramatically compared with when mares were on ad libitum pasture.…”

Variations of plasma leptin in show horses during a work season

“…However, not all studies confirm these findings (Gordon and McKeever, 2005), and daily fluctuations in leptin levels may be a consequence of the feeding schedule and/or feed composition. Leptin levels rise 8–10 h after a high carbohydrate (grain) meal and follow the rise in insulin levels (Steelman et al., 2007; Storer et al., 2007). In contrast, the observed peaks and troughs in insulin and leptin concentrations are blunted in horses receiving frequent meals, hay ad libitum or feeding on pasture (Storer et al., 2007).…”