Hoffman R M, Boston R C, Stefanovski D, Kronfeld D S, Harris P A
Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg 24061-0306, USA.
J Anim Sci. 2003 Sep;81(9):2333-42. doi: 10.2527/2003.8192333x.
Insulin resistance is considered a risk factor in obesity, laminitis, exertional rhabdomyolysis, and osteochondrosis. The objective was to use the minimal model to estimate glucose effectiveness (Sg) and insulin sensitivity (Si) in nonobese to obese horses initially adapted to forage only, then adapted to forage plus supplements rich in starch and sugar (SS) or fiber and fat (FF). Ten Thoroughbred geldings, with BCS of 5 (nonobese), 6 (moderately obese), and 7 to 8 (obese), were adapted to pasture and hay, allocated to two groups, and fed SS or FF in a switch-back design with 8 wk of adaptation. Modified frequent-sampling i.v. glucose tolerance tests were applied after adaptation to forage, SS, and FF. For the tolerance tests, horses were kept in stalls overnight and provided hay, and venous catheters were placed the next morning. Baseline samples were collected, 0.3 g of glucose/kg of BW was given i.v., and blood was sampled at 1, 2, 3, 4, 5, 6, 7, 8, 10, 12, 14, 16, and 19 min. At 20 min, 30 mU of insulin/kg of BW was given, followed by sampling at 22, 23, 24, 25, 27, 30, 35, 40, 50, 60, 70, 80, 90, 100, 120, 150, and 180 min. Plasma was analyzed for glucose and insulin, and Si, Sg, acute insulin response to glucose, and the disposition index were calculated. Normality was tested using the Shapiro-Wilk statistic. Body condition effects were analyzed using a mixed model with repeated measures. Diet effects were analyzed using a Wilcoxon signed rank test. The Sg was higher in obese than nonobese (P = 0.003) and moderately obese (P = 0.007) horses; Si was lower in obese than nonobese (P = 0.008) horses, and acute insulin response to glucose was higher in obese than nonobese (P = 0.039) horses. Effects of diet were likely confounded by body condition, but horses had lower Si (P = 0.066) when fed SS compared with FF, especially when nonobese. In conclusion, the minimal model effectively estimated Sg, Si, acute insulin response to glucose, and disposition index in horses. Obese geldings were insulin-resistant and seemed to rely primarily on Sg for glucose disposal. Feeding a diet rich in sugar and starch decreased insulin sensitivity of horses. Maintenance of body condition and avoidance of grain-based meals rich in sugar and starch would be beneficial to decrease the risk of developing insulin resistance and associated metabolic syndromes in horses, especially for horses at risk for these syndromes.
胰岛素抵抗被认为是肥胖、蹄叶炎、运动性横纹肌溶解症和骨软骨病的一个风险因素。目的是使用最小模型来估计最初仅适应粗饲料，然后适应添加富含淀粉和糖（SS）或纤维和脂肪（FF）补充剂的粗饲料的非肥胖至肥胖马匹的葡萄糖有效性（Sg）和胰岛素敏感性（Si）。十匹体重状况评分（BCS）为5（非肥胖）、6（中度肥胖）和7至8（肥胖）的纯种阉马，先适应牧场和干草，分为两组，并采用交叉设计，经过8周适应期分别饲喂SS或FF。在适应粗饲料、SS和FF后，进行改良的频繁静脉注射葡萄糖耐量试验。对于耐量试验，马匹在厩舍中过夜并提供干草，第二天早上放置静脉导管。采集基线样本，静脉注射0.3 g葡萄糖/kg体重，并在1、2、3、4、5、6、7、8、10、12、14、16和19分钟采集血样。在20分钟时，静脉注射30 mU胰岛素/kg体重，随后在22、23、24、25、27、30、35、40、50、60、70、80、90、100、120、150和180分钟采集血样。分析血浆中的葡萄糖和胰岛素，并计算Si、Sg、葡萄糖的急性胰岛素反应和处置指数。使用夏皮罗-威尔克统计量检验正态性。使用重复测量的混合模型分析体况效应。使用威尔科克森符号秩检验分析饮食效应。肥胖马匹的Sg高于非肥胖（P = 0.003）和中度肥胖（P = 0.007）马匹；肥胖马匹的Si低于非肥胖（P = 0.008）马匹，肥胖马匹对葡萄糖的急性胰岛素反应高于非肥胖（P = 0.039）马匹。饮食效应可能与体况混淆，但与FF相比，马匹饲喂SS时Si较低（P = 0.066），尤其是非肥胖马匹。总之，最小模型有效地估计了马匹的Sg、Si、葡萄糖的急性胰岛素反应和处置指数。肥胖阉马存在胰岛素抵抗，似乎主要依赖Sg进行葡萄糖代谢。饲喂富含糖和淀粉的日粮会降低马匹的胰岛素敏感性。维持体况并避免富含糖和淀粉的谷物类日粮，将有利于降低马匹发生胰岛素抵抗和相关代谢综合征的风险，特别是对于有这些综合征风险的马匹。
